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In
nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: st ...
,
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Development ...

biology
, and
chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. T ...

chemistry
, fat usually means any
ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a and an . s are s of ; they are important in biology, being one of the main classe ...

ester
of
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s, or a mixture of such
compounds Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive structu ...
, most commonly those that occur in living beings or in
food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contains essential nutrients, such as carbohydrates, fats, protein (nutrient), proteins, vi ...

food
. The term often refers specifically to
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
s (triple esters of
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
), that are the main components of
vegetable oil Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by ...
s and of in animals; or, even more narrowly, to triglycerides that are solid or semisolid at room temperature, thus excluding oils. The term may also be used more broadly as a synonym of
lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
—any substance of biological relevance, composed of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
,
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
, or
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, that is insoluble in water but soluble in
non-polar solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical flui ...
s. In this sense, besides the triglycerides, the term would include several other types of compounds like
mono- Numeral or number prefixes are prefix A prefix is an affix which is placed before the Word stem, stem of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''ha ...

mono-
and
diglyceride A diglyceride, or diacylglycerol (DAG), is a glyceride , the simplest possible fat after Triformin Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic. Glycer ...
s,
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s (such as
lecithin 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; – saturated fatty acid. Lecithin (, from the Greek ''lekithos'' "yolk") ...
),
sterol Sterol is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and synth ...

sterol
s (such as
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
),
wax Waxes are a diverse class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, ...
es (such as
beeswax foundation, made by pressing beeswax between patterned metal rollers Beeswax (''cera alba'') is a natural wax , a typical wax ester. Image:Beeswax foundation.jpg, Commercial honeycomb foundation, made by pressing beeswax between patterned m ...

beeswax
), and free fatty acids, which are usually present in human diet in smaller amounts. Fats are one of the three main
macronutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and ta ...
groups in human
diet Diet may refer to: Food * Diet (nutrition) In nutrition, diet is the sum of food consumed by a person or other organism. The word diet often implies the use of specific intake of nutrition for #Health, health or #Weight management, weight-mana ...
, along with
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s and
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s, and the main components of common food products like
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
,
butter Butter is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contai ...

butter
,
tallow Tallow is a rendering (industrial), rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain techni ...

tallow
,
lard Lard is a semi-solid white fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any indivi ...
,
salt pork Salt is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it i ...
, and
cooking oil Cooking oil is plant, animal, or synthetic fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') ...
s. They are a major and dense source of
food energy Food energy is chemical energy Chemical energy is the energy of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havin ...
for many animals and play important structural and
metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolic
functions, in most living beings, including energy storage, waterproofing, and
thermal insulation insulation, 1600 dpi scan Thermal insulation is the reduction of heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy Thermal radiation in visible li ...
. The human body can produce the fat it requires from other food ingredients, except for a few
essential fatty acid Essential fatty acids, or EFAs, are fatty acid fatty acids have perfectly straight chain structure. Unsaturated compound, Unsaturated ones are typically bent, unless they have a #Unsaturated fatty acids, trans configuration. In chemistry, parti ...
s that must be included in the diet. Dietary fats are also the carriers of some
flavor Flavor, or flavour, is the perceptual Perception (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area arou ...

flavor
and
aroma An odor (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...

aroma
ingredients and
vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...
s that are not water-soluble.


Biological importance

In humans and many animals, fats serve both as energy sources and as stores for energy in excess of what the body needs immediately. Each gram of fat when burned or metabolized releases about 9 food calories (37 = 8.8
kcal The calorie is a unit of energy As energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...
). Fats are also sources of
essential fatty acid Essential fatty acids, or EFAs, are fatty acid fatty acids have perfectly straight chain structure. Unsaturated compound, Unsaturated ones are typically bent, unless they have a #Unsaturated fatty acids, trans configuration. In chemistry, parti ...
s, an important dietary requirement.
Vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...
s , D, , and K are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats play a vital role in maintaining healthy
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differ ...

skin
and
hair Hair is a protein filament In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Ph ...

hair
, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function. Fat also serves as a useful buffer against a host of diseases. When a particular substance, whether chemical or biotic, reaches unsafe levels in the bloodstream, the body can effectively dilute—or at least maintain equilibrium of—the offending substances by storing it in new fat tissue. This helps to protect vital organs, until such time as the offending substances can be metabolized or removed from the body by such means as
excretion Excretion is a process in which metabolic waste Metabolic wastes or excrements are Chemical substance, substances left over from metabolism, metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus ...
,
urination Urination is the release of urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted ...
, accidental or intentional
bloodletting Bloodletting (or blood-letting) is the withdrawal of from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by es, was based on an ancient system of in which blood and other bodily fluids were regarded ...

bloodletting
,
sebum A sebaceous gland is a microscopic exocrine Exocrine glands are gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is a ...

sebum
excretion, and
hair Hair is a protein filament In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Ph ...

hair
growth.


Adipose tissue

In animals,
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biolo ...

adipose tissue
, or fatty tissue is the body's means of storing metabolic energy over extended periods of time.
Adipocyte Adipocytes, also known as lipocytes and fat cells, are the cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or ...

Adipocyte
s (fat cells) store fat derived from the diet and from liver
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
. Under energy stress these cells may degrade their stored fat to supply fatty acids and also glycerol to the
circulation Circulation may refer to: Science and technology * Atmospheric circulation, the large-scale movement of air * Circulation (physics), the path integral of the fluid velocity around a closed curve in a fluid flow field * Circulatory system, a biolo ...
. These metabolic activities are regulated by several hormones (e.g.,
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets; it is considered to be the main Anabolism, anabolic hormone of the body. It regulates the metabolism of carbohydrates, fats and p ...

insulin
,
glucagon Glucagon is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine ...

glucagon
and
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in ...

epinephrine
). Adipose tissue also secretes the hormone
leptin Leptin (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxima ...

leptin
. The location of the tissue determines its metabolic profile:
visceral fat Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesod ...
is located within the abdominal wall (i.e., beneath the wall of abdominal muscle) whereas
subcutaneous fat The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the hypodermis are fibroblasts, adipose cells, and m ...
is located beneath the skin (and includes fat that is located in the abdominal area beneath the skin but ''above'' the abdominal muscle wall). Visceral fat was recently discovered to be a significant producer of signaling chemicals (i.e.,
hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

hormone
s), among which several are involved in inflammatory tissue responses. One of these is which has been linked to obesity,
insulin resistance Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin. Insulin is a hormone that allows glucose to enter cells which also reduces blood glucose (blood sugar). Insulin is ...
, and Type 2 diabetes. This latter result is currently controversial, and there have been reputable studies supporting all sides on the issue.


Production and processing

A variety of chemical and physical techniques are used for the production and processing of fats, both industrially and in cottage or home settings. They include: * Pressing to extract liquid fats from fruits, seeds, or
alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from un ...

alga
e, e.g.
olive oil Olive oil is a liquid fat obtained from olive The olive, known by the botanical name ''Olea europaea'', meaning "European olive", is a species In biology, a species is the basic unit of biological classification, classification and ...

olive oil
from
olive The olive, botanical name ''Olea europaea'', meaning "European olive", is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodivers ...

olive
s; *
Solvent extraction A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical flui ...

Solvent extraction
using solvents like
hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. Hexane is a significant constituent of gasoline. It is a colorless liquid, odorless when pure, and with boiling points approxim ...

hexane
or
supercritical carbon dioxide upright=1.3, Carbon dioxide pressure-temperature phase diagram Supercritical carbon dioxide (s) is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a ...
. * Rendering, the melting of fat in adipose tissue, e.g. to produce tallow, lard,
fish oil Fish oil is oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyd ...
, and
whale oil Whale oil is oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All ev ...
. * Churning of milk to produce butter. *
Hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...
to lower the degree of unsaturation of the fatty acids. * Interesterification, the rearrangement of fatty acids across different triglycerides. * Winterization to remove oil components with higher melting points. * Clarification of butter.


Metabolism

The
pancreatic lipase Triglyceride lipases () are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, ...
acts at the ester bond, hydrolyzing the bond and "releasing" the fatty acid. In triglyceride form, lipids cannot be absorbed by the
duodenum The duodenum is the first section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from foo ...

duodenum
. Fatty acids, monoglycerides (one glycerol, one fatty acid), and some diglycerides are absorbed by the duodenum, once the triglycerides have been broken down. In the
intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, d ...

intestine
, following the secretion of
lipase A lipase (, ) is any enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules known as . Almost all ...
s and
bile Bile (from latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the of most s that aids the of s in the . In humans, bile is produced continuously by the liver (liver bile) and stored and concentrated in the . After ...
, triglycerides are split into monoacylglycerol and free fatty acids in a process called
lipolysis upright=1.8, Example of a triacylglycerol Lipolysis is the metabolic pathway In biochemistry Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry ...
. They are subsequently moved to absorptive
enterocyte Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biolo ...
cells lining the intestines. The triglycerides are rebuilt in the enterocytes from their fragments and packaged together with
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
and proteins to form
chylomicron Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein, lipoprotein particles that consist of trigl ...

chylomicron
s. These are excreted from the cells and collected by the lymph system and transported to the large vessels near the heart before being mixed into the blood. Various tissues can capture the chylomicrons, releasing the triglycerides to be used as a source of energy. Liver cells can synthesize and store triglycerides. When the body requires
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s as an energy source, the hormone
glucagon Glucagon is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine ...

glucagon
signals the breakdown of the triglycerides by hormone-sensitive lipase to release free fatty acids. As the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tiss ...

brain
cannot utilize fatty acids as an energy source (unless converted to a
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
), the
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
component of triglycerides can be converted into
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
, via
gluconeogenesis Gluconeogenesis (GNG) is a that results in the generation of from certain non- carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In vertebrates, gluconeogenesis occurs mainly i ...

gluconeogenesis
by conversion into
dihydroxyacetone phosphate Dihydroxyacetone phosphate (DHAP, also glycerone phosphate in older texts) is the anion with the formula HOCH2C(O)CH2OPO32-. This anion is involved in many metabolic pathways, including the Calvin cycle in plants and glycolysis.Nelson, D. L.; Cox ...
and then into
glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is the metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical ...

glyceraldehyde 3-phosphate
, for brain fuel when it is broken down. Fat cells may also be broken down for that reason if the brain's needs ever outweigh the body's. Triglycerides cannot pass through cell membranes freely. Special enzymes on the walls of blood vessels called
lipoprotein lipase Lipoprotein lipase (LPL) () is a member of the lipase A lipase (, ) is any enzyme that catalyzes the hydrolysis of fats (lipids). Lipases are a subclass of the esterases. Lipases perform essential roles in digestion, transport and processing of d ...
s must break down triglycerides into free fatty acids and glycerol. Fatty acids can then be taken up by cells via the fatty acid transporter (FAT). Triglycerides, as major components of
very-low-density lipoprotein Very-low-density lipoprotein (VLDL), density relative to extracellular water, is a type of lipoprotein made by the liver The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces ...
(VLDL) and
chylomicron Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein, lipoprotein particles that consist of trigl ...

chylomicron
s, play an important role in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
as energy sources and transporters of dietary fat. They contain more than twice as much energy (approximately 9
kcal The calorie is a unit of energy As energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...
/g or 38 kJ/g) as
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s (approximately 4
kcal The calorie is a unit of energy As energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...
/g or 17 kJ/g).


Nutritional and health aspects

The most common type of fat, in human diet and most living beings, is a
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
, an ester of the triple
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
and three fatty acids. The molecule of a triglyceride can be described as resulting from a
condensation reaction In , a condensation reaction is a type of in which two s are to form a single molecule, usually with the loss of a small molecule such as . If water is lost, the reaction is also known as a . However other molecules can also be lost, such as , , ...
(specifically,
esterification An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl ( alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycer ...

esterification
) between each of glycerol's –OH groups and the HO– part of the carboxyl group of each fatty acid, forming an ester bridge with elimination of a water molecule . Other less common types of fats include
diglycerides A diglyceride, or diacylglycerol (DAG), is a glyceride consisting of two fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistr ...
and
monoglycerides Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glyceride , the simplest possible fat after Triformin Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generall ...
, where the esterification is limited to two or just one of glycerol's –OH groups. Other alcohols, such as
cetyl alcohol Cetyl alcohol , also known as hexadecan-1-ol and palmityl alcohol, is a C-16 fatty alcohol with the chemical formula, formula CH3(CH2)15OH. At room temperature, cetyl alcohol takes the form of a waxy white solid or flakes. The name cetyl derives ...

cetyl alcohol
(predominant in
spermaceti Spermaceti (from Greek ''sperma'' meaning "seed", and '' ceti'', the genitive form of "whale") is a wax , a typical wax ester. Image:Beeswax foundation.jpg, Commercial honeycomb foundation, made by pressing beeswax between patterned metal roller ...

spermaceti
), may replace glycerol. In the
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s, one of the fatty acids is replaced by
phosphoric acid Phosphoric acid, also known as orthophosphoric acid or phosphoric(V) acid, is a weak acid with the chemical formula . The pure compound is a colorless solid. All three hydrogens are acidic to varying degrees and can be lost from the molecule a ...

phosphoric acid
or a monoester thereof. The benefits and risks of various amounts and types of dietary fats have been the object of much study, and are still highly controversial topics.


Essential fatty acids

There are two
essential fatty acids Essential fatty acids, or EFAs, are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. The term "essential fatty acid" refers to fatty acids required for biological p ...
(EFAs) in human nutrition:
alpha-linolenic acid α-Linolenic acid (ALA), (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxi ...

alpha-linolenic acid
(an
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This ...
) and
linoleic acid Linoleic acid is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules ...

linoleic acid
(an
omega-6 fatty acid of linoleic acid, a common omega-6 fatty acid found in many nuts, seeds A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering. The formation of the seed is part of the process of reprod ...
). Other lipids needed by the body can be synthesized from these and other fats.


Saturated vs. unsaturated fats

Different foods contain different amounts of fat with different proportions of saturated and unsaturated fatty acids. Some animal products, like beef and dairy products made with whole or reduced fat milk like yogurt, ice cream, cheese and
butter Butter is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contai ...

butter
have mostly saturated fatty acids (and some have significant contents of dietary cholesterol). Other animal products, like pork, poultry, Egg as food, eggs, and seafood have mostly unsaturated fats. Industrialized baked goods may use fats with high unsaturated fat contents as well, especially those containing hydrogenation, partially hydrogenated oils, and processed foods that are deep-fried in vegetable oil#Hydrogenated oils, hydrogenated oil are high in saturated fat content. Plants and fish oil generally contain a higher proportion of unsaturated acids, although there are exceptions such as coconut oil and palm kernel oil. Foods containing unsaturated fats include avocado, nut (fruit), nuts,
olive oil Olive oil is a liquid fat obtained from olive The olive, known by the botanical name ''Olea europaea'', meaning "European olive", is a species In biology, a species is the basic unit of biological classification, classification and ...

olive oil
s, and
vegetable oil Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by ...
s such as canola. Many careful studies have found that replacing saturated fats with ''cis'' unsaturated fats in the diet reduces risk of cardiovascular diseases, diabetes, or death. These studies prompted many medical organizations and public health departments, including the World Health Organization, to officially issue that advice. Some countries with such recommendations include: * United Kingdom * United States * India * Canada * Australia * Singapore * New Zealand * Hong Kong A 2004 review concluded that "no lower safe limit of specific saturated fatty acid intakes has been identified" and recommended that the influence of varying saturated fatty acid intakes against a background of different individual lifestyles and genetic backgrounds should be the focus in future studies. This advice is often oversimplified by labeling the two kinds of fats as ''bad fats'' and ''good fats'', respectively. However, since the fats and oils in most natural and traditionally processed foods contain both unsaturated and saturated fatty acids, the complete exclusion of saturated fat is unrealistic and possibly unwise. For instance, some foods rich in saturated fat, such as coconut and palm oil, are an important source of cheap dietary calories for a large fraction of the population in developing countries. Concerns were also expressed at a 2010 conference of the American Dietetic Association that a blanket recommendation to avoid saturated fats could drive people to also reduce the amount of polyunsaturated fats, which may have health benefits, and/or replace fats by refined carbohydrates — which carry a high risk of obesity and heart disease. For these reasons, the United States Food and Drug Administration (FDA), for example, does not advise the complete elimination of saturated fat, but only recommends that it does not exceed 30% of one's daily caloric intake. A 2003 report by the World Health Organization and the Food and Agriculture Organization (FAO) recommends limiting the saturated fatty acids to less than 10% of daily energy intake and less than 7% for high-risk groups. A general 7% limit was recommended also by the American Heart Association in 2006. The WHO/FAO report also recommended replacing fats so as to reduce the content of myristic and palmitic acids, specifically. The so-called Mediterranean diet, prevalent in many countries in the Mediterranean Sea area, includes more total fat than the diet of Northern European countries, but most of it is in the form of unsaturated fatty acids (specifically, monounsaturated and omega-3) from olive oil and fish, vegetables, and certain meats like lamb, while consumption of saturated fat is minimal in comparison. A 2017 review found evidence that a Mediterranean-style diet could reduce the risk of cardiovascular diseases, overall cancer incidence, neurodegenerative diseases, diabetes, and mortality rate. A 2018 review showed that a Mediterranean-like diet may improve overall health status, such as reduced risk of non-communicable diseases. It also may reduce the social and economic costs of diet-related illnesses. A small number of contemporary reviews have challenged this negative view of saturated fats. For example, an evaluation of evidence from 1966-1973 of the observed health impact of replacing dietary saturated fat with
linoleic acid Linoleic acid is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules ...

linoleic acid
found that it ''increased'' rates of death from all causes, coronary heart disease, and cardiovascular disease. These studies have been disputed by many scientists, and the consensus in the medical community is that saturated fat and cardiovascular disease are closely related. Still, these discordant studies fueled debate over the merits of substituting polyunsaturated fats for saturated fats.


Cardiovascular disease

The effect of saturated fat on cardiovascular disease has been extensively studied. The general consensus is that there is evidence of moderate-quality of a strong, consistent, and graded relationship between saturated fat intake, blood cholesterol levels, and the incidence of cardiovascular disease. The relationships are accepted as causal, including by many government and medical organizations. A 2017 review by the American Heart Association estimated that replacement of saturated fat with polyunsaturated fat in the American diet could reduce the risk of cardiovascular diseases by 30%. The consumption of saturated fat is generally considered a risk factor for dyslipidemia — abnormal blood lipid levels, including high total cholesterol, high levels of triglycerides, high levels of low-density lipoprotein (LDL, "bad" cholesterol) or low levels of high-density lipoprotein (HDL, "good" cholesterol). These parameters in turn are believed to be risk indicators for some types of cardiovascular disease. These effects were observed in children too. Several meta-analysis, meta-analyses (reviews and consolidations of multiple previously published experimental studies) have confirmed a significant relationship between saturated fat and high serum cholesterol levels, which in turn have been claimed to have a causal relation with increased risk of cardiovascular disease (the so-called lipid hypothesis). However, high cholesterol may be caused by many factors. Other indicators, such as high LDL/HDL ratio, have proved to be more predictive. In a study of myocardial infarction in 52 countries, the apolipoprotein B, ApoB/apolipoprotein A1, ApoA1 (related to LDL and HDL, respectively) ratio was the strongest predictor of CVD among all risk factors. There are other pathways involving obesity,
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
levels, insulin resistance, insulin sensitivity, endothelium, endothelial function, and thrombogenicity, among others, that play a role in CVD, although it seems, in the absence of an adverse blood lipid profile, the other known risk factors have only a weak atherogenic effect. Different saturated fatty acids have differing effects on various lipid levels.


Cancer

The evidence for a relation between saturated fat intake and cancer is significantly weaker, and there does not seem to be a clear medical consensus about it. * A meta-analysis published in 2003 found a epidemiology and etiology of breast cancer#Specific dietary fatty acidssignificant positive relationship between saturated fat and breast cancer. However two subsequent reviews have found weak or insignificant relation, and noted the prevalence of confounding factors. * Another review found limited evidence for a positive relationship between consuming animal fat and incidence of colorectal cancer. * Other meta-analyses found evidence for increased risk of ovarian cancer by high consumption of saturated fat. * Some studies have indicated that serum myristic acid and palmitic acid and dietary myristic and palmitic saturated fatty acids and serum palmitic combined with tocopherol#Alpha-tocopherol, alpha-tocopherol supplementation are Prostate cancer#Oils and fatty acids, associated with increased risk of prostate cancer in a dose-dependent manner. These associations may, however, reflect differences in intake or metabolism of these fatty acids between the precancer cases and controls, rather than being an actual cause.


Bones

Various animal studies have indicated that the intake of saturated fat has a negative effect on effects on the osteoporosis, mineral density of bones. One study suggested that men may be particularly vulnerable.


Disposition and overall health

Studies have shown that substituting monounsaturated fatty acids for saturated ones is associated with increased daily physical activity and resting energy expenditure. More physical activity, less anger, and less irritability were associated with a higher-oleic acid diet than one of a palmitic acid diet.


Monounsaturated vs. polyunsaturated fat

Assuming given that unsaturated fatty acids (UFAs) are generally healthier than saturated ones (SFAs), another question that has gained attention in recent decades is the risks and benefits of monounsaturated fatty acids (MUFAs, with a single double bond) versus polyunsaturated fatty acids (PUFAs, with two or more double bonds). The most common fatty acids in human diet are unsaturated or mono-unsaturated. Monounsaturated fats are found in animal flesh such as red meat, whole milk products, Nut (fruit), nuts, and high fat fruits such as olives and avocados. Olive oil is about 75% monounsaturated fat. The high oleic variety sunflower oil contains at least 70% monounsaturated fat. Canola oil and cashews are both about 58% monounsaturated fat. Tallow (beef fat) is about 50% monounsaturated fat. and
lard Lard is a semi-solid white fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any indivi ...
is about 40% monounsaturated fat. Other sources include hazelnut, avocado oil, macadamia nut oil, Grape seed oil, grapeseed oil, groundnut oil (peanut oil), sesame oil, corn oil, popcorn, whole grain wheat, cereal, oatmeal, almond oil, sunflower oil, hemp oil, and tea-oil Camellia. Polyunsaturated fatty acids can be found mostly in nuts, seeds, fish, seed oils, and oysters. Food sources of polyunsaturated fats include:


Insulin resistance and sensitivity

MUFAs (especially oleic acid) have been found to lower the incidence of
insulin resistance Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin. Insulin is a hormone that allows glucose to enter cells which also reduces blood glucose (blood sugar). Insulin is ...
PUFAs (especially large amounts of arachidonic acid) and SFAs (such as arachidic acid) increased it. These ratios can be indexed in the
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s of human skeletal muscle and in other tissues as well. This relationship between dietary fats and insulin resistance is presumed secondary to the relationship between insulin resistance and inflammation, which is partially modulated by dietary fat ratios (Omega-3 fatty acids, Omega-3/Omega-6 fatty acids, 6/Omega-9 fatty acids, 9) with both omega 3 and 9 thought to be anti-inflammatory, and omega 6 pro-inflammatory (as well as by numerous other dietary components, particularly Health effects of polyphenols, polyphenols and exercise, with both of these anti-inflammatory). Although both pro- and anti-inflammatory types of fat are biology, biologically necessary, fat dietary ratios in most US diets are skewed towards Omega 6, with subsequent disinhibition of inflammation and potentiation of insulin resistance. But this is contrary to the suggestion of more recent studies, in which polyunsaturated fats are shown as protective against insulin resistance. The large scale KANWU study found that increasing MUFA and decreasing SFA intake could improve insulin sensitivity, but only when the overall fat intake of the diet was low. However, some MUFAs may promote
insulin resistance Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin. Insulin is a hormone that allows glucose to enter cells which also reduces blood glucose (blood sugar). Insulin is ...
(like the SFAs), whereas PUFAs may protect against it.


Cancer

Levels of oleic acid along with other MUFAs in red blood cell membranes were positively associated with breast cancer risk. The saturation index (SI) of the same membranes was inversely associated with breast cancer risk. MUFAs and low SI in erythrocyte membranes are predictors of postmenopausal breast cancer. Both of these variables depend on the activity of the enzyme delta-9 desaturase (Δ9-d). Results from observational study, observational clinical trials on PUFA intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk. Some studies have shown associations between higher intakes and/or blood levels of omega-3 PUFAs and a decreased risk of certain cancers, including breast and colorectal cancer, while other studies found no associations with cancer risk.


Pregnancy disorders

Polyunsaturated fat supplementation was found to have no effect on the incidence of pregnancy-related disorders, such as hypertension or preeclampsia, but may increase the length of gestation slightly and decreased the incidence of early premature births. Expert panels in the United States and Europe recommend that pregnant and lactating women consume higher amounts of polyunsaturated fats than the general population to enhance the DHA status of the fetus and newborn.


"Cis fat" vs. "trans fat"

In nature, unsaturated fatty acids generally have double bonds in cis–trans isomerism, ''cis'' configuration (with the adjacent C–C bonds on the same side) as opposed to ''trans''. Nevertheless, Trans fat, ''trans'' fatty acids (TFAs) occur in small amounts in meat and milk of ruminants (such as cattle and sheep), typically 2–5% of total fat. Natural TFAs, which include conjugated linoleic acid (CLA) and vaccenic acid, originate in the rumen of these animals. CLA has two double bonds, one in the ''cis'' configuration and one in ''trans'', which makes it simultaneously a ''cis''- and a ''trans''-fatty acid. Concerns about ''trans'' fatty acids in human diet were raised when they were found to be an unintentional byproduct of the fat hydrogenation, partial hydrogenation of vegetable and fish oils. While these ''trans'' fatty acids (popularly called "trans fats") are edible, they have been implicated in many health problems. The hydrogenation process, invented and patented by Wilhelm Normann in 1902, made it possible to turn relatively cheap liquid fats such as whale oil, whale or
fish oil Fish oil is oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyd ...
into more solid fats and to extend their shelf-life by preventing rancidification. (The source fat and the process were initially kept secret to avoid consumer distaste.) This process was widely adopted by the food industry already in the early 1900s; first for the production of margarine, a replacement for butter and shortening, and eventually for various other fats used in snack food, packaged baked goods, and deep fried products. Full hydrogenation of a fat or oil produces a fully saturated fat. However, hydrogenation generally was interrupted before completion, to yield a fat product with specific melting point, hardness, and other properties. Unfortunately, partial hydrogenation turns some of the ''cis'' double bonds into ''trans'' bonds by an isomerization reaction. The trans configuration is favored because it is the lower energy form. This side reaction accounts for most of the ''trans'' fatty acids consumed today, by far. An analysis of some industrialized foods in 2006 found up to 30% "trans fats" in artificial shortening, 10% in breads and cake products, 8% in cookies and crackers, 4% in salty snacks, 7% in cake frostings and sweets, and 26% in margarine and other processed spreads. Another 2010 analysis however found only 0.2% of trans fats in margarine and other processed spreads. Up to 45% of the total fat in those foods containing man-made ''trans'' fats formed by partially hydrogenating plant fats may be ''trans'' fat. Baking shortenings, unless reformulated, contain around 30% ''trans'' fats compared to their total fats. High-fat dairy products such as butter contain about 4%. Margarines not reformulated to reduce ''trans'' fats may contain up to 15% ''trans'' fat by weight, but some reformulated ones are less than 1% trans fat. High levels of TFAs have been recorded in popular "fast food" meals. An analysis of samples of McDonald's French fries collected in 2004 and 2005 found that fries served in New York City contained twice as much trans fat as in Hungary, and 28 times as much as in Denmark, where trans fats are restricted. For Kentucky Fried Chicken products, the pattern was reversed: the Hungarian product containing twice the trans fat of the New York product. Even within the United States, there was variation, with fries in New York containing 30% more trans fat than those from Atlanta.


Cardiovascular disease

Numerous studies have found that consumption of TFAs increases risk of cardiovascular disease. The Harvard School of Public Health advises that replacing TFAs and saturated fats with ''cis'' monounsaturated and polyunsaturated fats is beneficial for health. Consuming trans fats has been shown to increase the risk of coronary artery disease in part by raising levels of low-density lipoprotein (LDL, often termed "bad cholesterol"), lowering levels of high-density lipoprotein (HDL, often termed "good cholesterol"), increasing triglycerides in the bloodstream and promoting systemic inflammation. The primary health risk identified for trans fat consumption is an elevated risk of coronary artery disease (CAD). A 1994 study estimated that over 30,000 cardiac deaths per year in the United States are attributable to the consumption of trans fats. By 2006 upper estimates of 100,000 deaths were suggested. A comprehensive review of studies of trans fats published in 2006 in the New England Journal of Medicine reports a strong and reliable connection between trans fat consumption and CAD, concluding that "On a per-calorie basis, trans fats appear to increase the risk of CAD more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3% of total energy intake)". The major evidence for the effect of trans fat on CAD comes from the Nurses' Health Study – a cohort study that has been following 120,000 female nurses since its inception in 1976. In this study, Hu and colleagues analyzed data from 900 coronary events from the study's statistical population, population during 14 years of followup. He determined that a nurse's CAD risk roughly doubled (relative risk of 1.93, confidence interval, CI: 1.43 to 2.61) for each 2% increase in trans fat calories consumed (instead of carbohydrate calories). By contrast, for each 5% increase in saturated fat calories (instead of carbohydrate calories) there was a 17% increase in risk (relative risk of 1.17, confidence interval, CI: 0.97 to 1.41). "The replacement of saturated fat or trans unsaturated fat by cis (unhydrogenated) unsaturated fats was associated with larger reductions in risk than an isocaloric replacement by carbohydrates." Hu also reports on the benefits of reducing trans fat consumption. Replacing 2% of
food energy Food energy is chemical energy Chemical energy is the energy of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havin ...
from trans fat with non-trans unsaturated fats more than halves the risk of CAD (53%). By comparison, replacing a larger 5% of food energy from saturated fat with non-trans unsaturated fats reduces the risk of CAD by 43%. Another study considered deaths due to CAD, with consumption of trans fats being linked to an increase in mortality, and consumption of polyunsaturated fats being linked to a decrease in mortality. Trans fat has been found to act like saturated in raising the blood level of LDL ("bad cholesterol"); but, unlike saturated fat, it also decreases levels of HDL ("good cholesterol"). The net increase in LDL/HDL ratio with trans fat, a widely accepted indicator of risk for coronary artery, is approximately double that due to saturated fat. One randomized crossover study published in 2003 comparing the effect postprandial, of eating a meal on blood lipids of (relatively) cis and trans-fat-rich meals showed that cholesteryl ester transfer (CET) was 28% higher after the trans meal than after the cis meal and that lipoprotein concentrations were enriched in apolipoprotein(a) after the trans meals. The cytokine, citokyne test is a potentially more reliable indicator of CAD risk, although is still being studied. A study of over 700 nurses showed that those in the highest quartile of trans fat consumption had blood levels of C-reactive protein (CRP) that were 73% higher than those in the lowest quartile.


Breast feeding

It has been established that ''trans'' fats in human breast milk fluctuate with maternal consumption of trans fat, and that the amount of trans fats in the bloodstream of breastfed infants fluctuates with the amounts found in their milk. In 1999, reported percentages of trans fats (compared to total fats) in human milk ranged from 1% in Spain, 2% in France, 4% in Germany, and 7% in Canada and the United States.


Other health risks

There are suggestions that the negative consequences of trans fat consumption go beyond the cardiovascular risk. In general, there is much less scientific consensus asserting that eating trans fat specifically increases the risk of other chronic health problems: * Alzheimer's disease: A study published in Archives of Neurology in February 2003 suggested that the intake of both trans fats and saturated fats promotes the development of Alzheimer disease, although not confirmed in an animal model. It has been found that trans fats impaired memory and learning in middle-age rats. The brains of rats that ate trans-fats had fewer proteins critical to healthy neurological function. Inflammation in and around the hippocampus, the part of the brain responsible for learning and memory. These are the exact types of changes normally seen at the onset of Alzheimer's, but seen after six weeks, even though the rats were still young. * Cancer: There is no scientific consensus that consuming trans fats significantly increases cancer risks across the board. The American Cancer Society states that a relationship between trans fats and cancer "has not been determined." One study has found a positive connection between trans fat and prostate cancer. However, a larger study found a correlation between trans fats and a significant decrease in high-grade prostate cancer. An increased intake of trans fatty acids may raise the risk of breast cancer by 75%, suggest the results from the French part of the European Prospective Investigation into Cancer and Nutrition. * Diabetes: There is a growing concern that the risk of diabetes mellitus type 2, type 2 diabetes increases with trans fat consumption. However, consensus has not been reached. For example, one study found that risk is higher for those in the highest quartile of trans fat consumption. Another study has found no diabetes risk once other factors such as total fat intake and BMI were accounted for. * Obesity: Research indicates that trans fat may increase weight gain and abdominal fat, despite a similar caloric intake. A 6-year experiment revealed that monkeys fed a trans fat diet gained 7.2% of their body weight, as compared to 1.8% for monkeys on a mono-unsaturated fat diet. Although obesity is frequently linked to trans fat in the popular media, this is generally in the context of eating too many calories; there is not a strong scientific consensus connecting trans fat and obesity, although the 6-year experiment did find such a link, concluding that "under controlled feeding conditions, long-term TFA consumption was an independent factor in weight gain. TFAs enhanced intra-abdominal deposition of fat, even in the absence of caloric excess, and were associated with insulin resistance, with evidence that there is impaired post-insulin receptor binding signal transduction." * Female infertility, Infertility in women: One 2007 study found, "Each 2% increase in the intake of energy from trans unsaturated fats, as opposed to that from carbohydrates, was associated with a 73% greater risk of ovulatory infertility...". * Major depressive disorder: Spanish researchers analysed the diets of 12,059 people over six years and found that those who ate the most trans fats had a 48 per cent higher risk of depression than those who did not eat trans fats. One mechanism may be trans-fats' substitution for docosahexaenoic acid (DHA) levels in the orbitofrontal cortex (OFC). Very high intake of trans-fatty acids (43% of total fat) in mice from 2 to 16 months of age was associated with lowered DHA levels in the brain (p=0.001). When the brains of 15 major depressive subjects who had committed suicide were examined post-mortem and compared against 27 age-matched controls, the suicidal brains were found to have 16% less (male average) to 32% less (female average) DHA in the OFC. The OFC controls Reward (psychology), reward, reward expectation, and empathy (all of which are reduced in depressive mood disorders) and regulates the limbic system. * Behavioral irritability and aggression: a 2012 observational analysis of subjects of an earlier study found a strong relation between dietary trans fat acids and self-reported behavioral aggression and irritability, suggesting but not establishing causality. * Diminished memory: In a 2015 article, researchers re-analyzing results from the 1999-2005 UCSD Statin Study argue that "greater dietary trans fatty acid consumption is linked to worse word memory in adults during years of high productivity, adults age <45". * Acne: According to a 2015 study, trans fats are one of several components of Western pattern diets which promote acne, along with
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s with high glycemic load such as white sugar, refined sugars or refined grains, refined starches,
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
and dairy products, and saturated fats, while
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This ...
s, which reduce acne, are deficient in Western pattern diets.


Biochemical mechanisms

The exact biochemistry, biochemical process by which trans fats produce specific health problems are a topic of continuing research. Intake of dietary trans fat perturbs the body's ability to metabolize
essential fatty acid Essential fatty acids, or EFAs, are fatty acid fatty acids have perfectly straight chain structure. Unsaturated compound, Unsaturated ones are typically bent, unless they have a #Unsaturated fatty acids, trans configuration. In chemistry, parti ...
s (EFAs, including Omega-3 fatty acid, Omega-3) leading to changes in the phospholipid fatty acid composition of the arterial walls, thereby raising risk of coronary artery disease. Trans double bonds are claimed to induce a linear conformational isomerism, conformation to the molecule, favoring its rigid packing as in atheroma, plaque formation. The geometry of the ''cis'' double bond, in contrast, is claimed to create a bend in the molecule, thereby precluding rigid formations.. While the mechanisms through which trans fatty acids contribute to coronary artery disease are fairly well understood, the mechanism for their effects on diabetes is still under investigation. They may impair the metabolism of long-chain polyunsaturated fatty acids (LCPUFAs). However, maternal pregnancy trans fatty acid intake has been inversely associated with LCPUFAs levels in infants at birth thought to underlie the positive association between breastfeeding and intelligence. Trans fats are processed by the liver differently than other fats. They may cause liver function, liver dysfunction by interfering with delta 6 desaturase, an enzyme involved in converting essential fatty acids to arachidonic acid and prostaglandins, both of which are important to the functioning of cells.


Natural "trans fats" in dairy products

Some ''trans'' fatty acids occur in natural fats and traditionally processed foods. Vaccenic acid occurs in breast milk, and some isomers of conjugated linoleic acid (CLA) are found in meat and dairy products from ruminants. Butter, for example, contains about 3% trans fat. The US National Dairy Council has asserted that the trans fats present in animal foods are of a different type than those in partially hydrogenated oils, and do not appear to exhibit the same negative effects. While a recent scientific review agrees with the conclusion (stating that "the sum of the current evidence suggests that the Public health implications of consuming trans fats from ruminant products are relatively limited"), it cautions that this may be due to the low consumption of trans fats from animal sources compared to artificial ones. More recent inquiry (independent of the dairy industry) has found in a 2008 Dutch meta-analysis that all trans fats, regardless of natural or artificial origin equally raise LDL and lower HDL levels. Other studies though have shown different results when it comes to animal-based trans fats like conjugated linoleic acid (CLA). Although CLA is known for its anticancer properties, researchers have also found that the cis-9, trans-11 form of CLA can reduce the risk for cardiovascular disease and help fight inflammation. Two Canadian studies have shown that vaccenic acid, a TFA that naturally occurs in dairy products, could be beneficial compared to hydrogenated vegetable shortening, or a mixture of pork lard and soy fat, by lowering total LDL and triglyceride levels. A study by the US Department of Agriculture showed that vaccenic acid raises both HDL and LDL cholesterol, whereas industrial trans fats only raise LDL with no beneficial effect on HDL.


Official recommendations

In light of recognized evidence and scientific agreement, nutritional authorities consider all trans fats equally harmful for health and recommend that their consumption be reduced to trace amounts. The World Health Organization recommended that trans fats make up no more than 0.9% of a person's diet in 2003 and, in 2018, introduced a 6-step guide to eliminate industrially-produced trans-fatty acids from the global food supply. The United States National Academy of Sciences, National Academy of Sciences (NAS) advises the United States and Canadian governments on nutritional science for use in public policy and product labeling programs. Their 2002 ''Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids'' contains their findings and recommendations regarding consumption of trans fat
summary
). Their recommendations are based on two key facts. First, "trans fatty acids are not essential and provide no known benefit to human health", whether of animal or plant origin. Second, given their documented effects on the LDL/HDL ratio, the NAS concluded "that dietary trans fatty acids are more deleterious with respect to coronary artery disease than saturated fatty acids". A 2006 review published in the New England Journal of Medicine (NEJM) that states "from a nutritional standpoint, the consumption of trans fatty acids results in considerable potential harm but no apparent benefit." Because of these facts and concerns, the NAS has concluded there is no safe level of trans fat consumption. There is no adequate level, recommended daily amount or tolerable upper limit for trans fats. This is because any incremental increase in trans fat intake increases the risk of coronary artery disease. Despite this concern, the NAS dietary recommendations have not included eliminating trans fat from the diet. This is because trans fat is naturally present in many animal foods in trace quantities, and thus its removal from ordinary diets might introduce undesirable side effects and nutritional imbalances. The NAS has, thus, "recommended that trans fatty acid consumption be as low as possible while consuming a nutritionally adequate diet". Like the NAS, the World Health Organization has tried to balance public health goals with a practical level of trans fat consumption, recommending in 2003 that trans fats be limited to less than 1% of overall energy intake.


Regulatory action

In the last few decades, there has been substantial amount of trans fat regulation, regulation in many countries, limiting trans fat contents of industrialized and commercial food products.


Alternatives to hydrogenation

In recent years, the negative public image and strict regulations have driven many fat processing industries to replace partial hydrogenation by fat interesterification, a process that chemically scrambles the fatty acids among a mix of triglycerides. When applied to a suitable bend of oils and saturated fats, possibly followed by separation of unwanted solid or liquid triglycerides, this process can achieve results similar to those of partial hydrogenation without affecting the fatty acids themselves; in particular, without creating any new "trans fat". Researchers at the United States Department of Agriculture have investigated whether hydrogenation can be achieved without the side effect of trans fat production. They varied the pressure under which the chemical reaction was conducted – applying 1400 Pascal (unit), kPa (200 pound-force per square inch, psi) of pressure to soybean oil in a 2-liter vessel while heating it to between 140 °C and 170 °C. The standard 140 kPa (20 psi) process of hydrogenation produces a product of about 40% trans fatty acid by weight, compared to about 17% using the high-pressure method. Blended with unhydrogenated liquid soybean oil, the high-pressure-processed oil produced margarine containing 5 to 6% trans fat. Based on current U.S. labeling requirements (see below), the manufacturer could claim the product was free of trans fat. The level of trans fat may also be altered by modification of the temperature and the length of time during hydrogenation. A University of Guelph research group has found a way to mix oils (such as olive, soybean, and canola), water, monoglycerides, and fatty acids to form a "cooking fat" that acts the same way as trans and saturated fats.


Omega-three and omega-six fatty acids

The Omega-3 fatty acid, ω−3 fatty acids have received substantial attention in recent years. Among omega-3 fatty acids, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic acid (DHA), however, the most abundant omega-3 polyunsaturated fatty acid in erythrocyte (red blood cell) membranes, were associated with a reduced risk of breast cancer. The Docosahexaenoic acid, DHA obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance. In addition Docosahexaenoic acid, DHA is vital for the Grey matter , grey matter structure of the human brain, as well as retinal stimulation and neurotransmission.


Interesterification

Some studies have investigated the health effects of insteresterified (IE) fats, by comparing diets with IE and non-IE fats with the same overall fatty acid composition. Several experimental studies in humans found no statistical difference on fasting blood lipids between a with large amounts of IE fat, having 25-40% C16:0 or C18:0 on the 2-position, and a similar diet with non-IE fat, having only 3-9% C16:0 or C18:0 on the 2-position. A negative result was obtained also in a study that compared the effects on blood
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
levels of an IE fat product mimicking cocoa butter and the real non-IE product. A 2007 study funded by the Malaysian Palm Oil Board claimed that replacing natural palm oil by other interesterified or partial hydrogenated fats caused adverse health effects, such as higher low-density lipoprotein, LDL/high-density lipoprotein, HDL ratio and plasma glucose levels. However, these effects could be attributed to the higher percentage of saturated acids in the IE and partially hydrogenated fats, rather than to the IE process itself.


Role in disease

In the human body, high levels of triglycerides in the bloodstream have been linked to atherosclerosis, Coronary heart disease, heart disease and stroke. However, the relative negative impact of raised levels of triglycerides compared to that of Low-density lipoprotein, LDL:High-density lipoprotein, HDL ratios is as yet unknown. The risk can be partly accounted for by a strong inverse relationship between triglyceride level and HDL-cholesterol level. But the risk is also due to high triglyceride levels increasing the quantity of Low-density lipoprotein#LDL subtype patterns, small, dense LDL particles.


Guidelines

The National Cholesterol Education Program has set guidelines for triglyceride levels: These levels are tested after fasting#Medical application, fasting 8 to 12 hours. Triglyceride levels remain temporarily higher for a period after eating. The American Heart Association recommends an optimal triglyceride level of 100mg/dL (1.1mmol/L) or lower to improve heart health.


Reducing triglyceride levels

Weight loss and dietary modification are effective first-line lifestyle modification treatments for hypertriglyceridemia. For people with mildly or moderately high levels of triglycerides, lifestyle changes, including weight loss, moderate exerciseCrawford, H., Micheal. ''Current Diagnosis & Treatment Cardiology''. 3rd ed. McGraw-Hill Medical, 2009. p21 and dietary modification, are recommended. This may include restriction of carbohydrates (specifically fructose) and fat in the
diet Diet may refer to: Food * Diet (nutrition) In nutrition, diet is the sum of food consumed by a person or other organism. The word diet often implies the use of specific intake of nutrition for #Health, health or #Weight management, weight-mana ...
and the consumption of
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This ...
s from algae, nuts, fish and seeds. Medications are recommended in those with high levels of triglycerides that are not corrected with the aforementioned lifestyle modifications, with fibrates being recommended first. Omega-3-carboxylic acids is another prescription drug used to treat very high levels of blood triglycerides. The decision to treat hypertriglyceridemia with medication depends on the levels and on the presence of other risk factors for cardiovascular disease. Very high levels that would increase the risk of pancreatitis is treated with a drug from the fibrate class. Niacin and
omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This ...
s as well as drugs from the statin class may be used in conjunction, with statins being the main medication for moderate hypertriglyceridemia when reduction of cardiovascular risk is required.


Fat digestion and metabolism

Fats are broken down in the healthy body to release their constituents, Glycerin, glycerol and
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s. Glycerol itself can be converted to
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
by the liver and so become a source of energy. Fats and other lipids are broken down in the body by enzymes called
lipase A lipase (, ) is any enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules known as . Almost all ...
s produced in the pancreas. Many cell types can use either glucose or fatty acids as a source of energy for metabolism. In particular, heart and skeletal muscle prefer fatty acids. Despite long-standing assertions to the contrary, fatty acids can also be used as a source of fuel for brain cells through mitochondrial oxidation.


See also

* Animal fat * Diet and heart disease * Fatty acid synthesis * Food composition data * Western pattern diet


References

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