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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 having volume. All everyday objects th ...
that animals (including
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

human
s) derive from their
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
and molecular oxygen through the process of
cellular respiration upright=2.5, Typical eukaryotic cell Cellular respiration is a set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities ...

cellular respiration
. Cellular respiration involves either the process of joining
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
from air with the
molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion I ...

molecule
s of food (aerobic respiration) or the process of reorganizing the
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atom ...

atom
s within the molecules (
anaerobic respiration Anaerobic respiration is respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenan ...
). Humans and other animals need a minimum intake of food energy to sustain their
metabolism 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 ...

metabolism
and to drive their muscles. Foods are composed chiefly of
carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common ex ...
s,
fat 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 ...

fat
s,
proteins 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 ...
,
water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , even though it provide ...

water
,
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, and
minerals 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 is composed, and the proces ...
. Carbohydrates, fats, proteins, and water represent virtually all the weight of food, with vitamins and minerals making up only a small percentage of the weight. (Carbohydrates, fats, and proteins comprise ninety percent of the dry weight of foods.) Organisms derive food energy from carbohydrates, fats and proteins as well as from
organic acid An organic acid is an with ic properties. The most common organic acids are the s, whose acidity is associated with their  –COOH. s, containing the group –SO2OH, are relatively stronger acids. Alcohols, with , can act as acids but t ...
s,
polyol A polyol 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 synt ...
s, and
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
present in the diet. Some
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 ...
components that provide little or no food energy, such as water, minerals, vitamins, cholesterol, and fiber, may still be necessary to health and survival for other reasons. Water, minerals, vitamins, and cholesterol are not broken down (they are used by the body in the form in which they are absorbed) and so cannot be used for energy. Fiber, a type of carbohydrate, cannot be completely digested by the human body.
Ruminant Ruminants ( Ruminantia) are large herbivorous grazing or browsing s that are able to acquire nutrients from plant-based food by it in a specialized prior to digestion, principally through microbial actions. The process, which takes place in th ...
s can extract food energy from the respiration of
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
because of
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sm ...

bacteria
in their
rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminant Ruminants (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recog ...
s. Using the
International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms_and_initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wi ...
, researchers measure energy in
joule The joule ( ; symbol: J) is a SI derived unit, derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work (physics), work done on) an object when a force of one Newton (unit), newton acts on th ...

joule
s (J) or in its multiples; the
kilojoule The joule ( ; symbol: J) is a derived unit of energy In physics, energy is the physical quantity, quantitative physical property, property that must be #Energy transfer, transferred to a physical body, body or physical system to perform W ...
(kJ) is most often used for food-related quantities. An older
metric system The metric system is a that succeeded the decimalised system based on the introduced in France in the 1790s. The historical development of these systems culminated in the definition of the (SI), under the oversight of an international stan ...

metric system
unit of energy, still widely used in food-related contexts, is the
calorie The calorie is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a di ...
; more precisely, the "food calorie", "large calorie" or
kilocalorie 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 ...
(kcal or Cal), equal to 4.184 kilojoules. Within the
European Union The European Union (EU) is a political and economic union of member states that are located primarily in Europe Europe is a which is also recognised as part of , located entirely in the and mostly in the . It comprises the wester ...

European Union
, both the kilocalorie ("kcal") and kilojoule ("kJ") appear on nutrition labels. In many countries, only one of the units is displayed; in the US and Canada labels spell out the unit as "calorie" or as "Calorie". Fats and ethanol have the greatest amount of food energy per mass, , respectively. Proteins and most carbohydrates have about . The differing
energy density In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...

energy density
of foods (fat, alcohols, carbohydrates and proteins) lies mainly in their varying proportions of carbon, hydrogen, and oxygen atoms: For food of elemental composition C''c''H''h''O''o''N''n'', the heat of combustion underlying the food energy is given by the empirical formula 420\,\mathrm \cdot \frac, to a good approximation (±3%). Carbohydrates that are not easily absorbed, such as fiber, or
lactose Lactose, a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-g ...

lactose
in lactose-intolerant individuals, contribute less food energy. Polyols (including
sugar alcohol Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, e ...
s) and organic acids contribute respectively. The amount of water, fat, and fiber in foods determines those foods' energy density. Theoretically, one could measure food energy in different ways, using (say) the
Gibbs free energy In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quan ...
of combustion, or the amount of
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
generated by metabolizing the food. However, the convention is to use the heat of the oxidation reaction, with the
water substance Water () is a polar inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, pr ...
produced being in the liquid phase. Conventional food energy is based on heats of combustion in a
bomb calorimeter A calorimeter is an object used for calorimetry upSnellen direct calorimetry chamber, University of Ottawa. Calorimetry is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transf ...
and corrections that take into consideration the efficiency of digestion and absorption and the production of
urea Urea, also known as carbamide, 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 prop ...

urea
and other substances in the urine. The American chemist worked these corrections out in the late 19th century. (See Atwater system for more detail.) Each food item has a specific metabolizable energy intake (MEI). This value can be approximated by multiplying the total amount of energy associated with a food item by 85%, which is the typical amount of energy actually obtained by a human after respiration has been completed. In animal nutrition, where energy is a critical element of the economics of meat production, researchers may determine a specific metabolizable energy for each component (protein, fat, etc.) of each ingredient of the feed.


Nutrition labels

Many governments require food manufacturers to label the energy content of their products, to help consumers control their energy intake.European Union regulations on nutrition labeling
/ref> In the European Union, manufacturers of packaged food must label the nutritional energy of their products in both kilocalories and kilojoules, when required. In the United States, the equivalent mandatory labels display only "Calories",United States federal food-labeling regulation

/ref> often as a substitute for the name of the quantity being measured, food energy; an additional kilojoules figure is optional and is rarely used. In Australia and New Zealand, the food energy must be stated in kilojoules (and optionally in kilocalories as well), and other nutritional energy information is similarly conveyed in kilojoules. The energy available from the respiration of food is usually given on labels for 100 g, for a typical serving size (according to the manufacturer), and/or for the entire pack contents. The amount of food energy associated with a particular food could be measured by completely burning the dried food in a
bomb calorimeter A calorimeter is an object used for calorimetry upSnellen direct calorimetry chamber, University of Ottawa. Calorimetry is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transf ...

bomb calorimeter
, a method known as direct
calorimetry upSnellen direct calorimetry chamber, University of Ottawa. Calorimetry is the science or act of measuring changes in ''state variables'' of a body for the purpose of deriving the heat transfer associated with changes of its state due, for exam ...
. However, the values given on food labels are not determined in this way. The reason for this is that direct calorimetry also burns the
dietary fiber Dietary fiber (British spelling fibre) or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzyme Digestive may refer to: Biology *Digestion Digestion is the breakdown of large insolubl ...
, and so does not allow for fecal losses; thus direct calorimetry would give systematic overestimates of the amount of fuel that actually enters the blood through digestion. What are used instead are standardized chemical tests or an analysis of the recipe using reference tables for common ingredients to estimate the product's digestible constituents (
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
,
carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common ex ...
,
fat 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 ...

fat
, etc.). These results are then converted into an equivalent energy value based on the following standardized table of energy densities.United Kingdo
The Food Labelling Regulations 1996
&ndash
Schedule 7: Nutrition labelling
/ref>Council directive 90/496/EEC of 24 September 1990 on nutrition labelling for foodstuffs
/ref> However "energy density" is a misleading term for it once again assumes that energy is IN the particular food, whereas it simply means that "high density" food needs more oxygen during respiration, leading to greater transfer of energy. Note that the following standardized table of energy densities is an approximation and the value in kJ/g does not convert exactly to kcal/g using a conversion factor. All the other nutrients in food are noncaloric and are thus not counted.


Recommended daily intake

Increased mental activity has been linked with moderately increased .Evaluation of a ''mental effort'' hypothesis for correlations between cortical metabolism and intelligence
Intelligence, Volume 21, Number 3, November 1995 , pp. 267-278(12), 1995.
Older people and those with
sedentary lifestyle A sedentary lifestyle is a lifestyle Lifestyle often refers to: * Lifestyle (sociology), the way a person lives * ''Otium'', ancient Roman concept of a lifestyle * Style of life (german: Lebensstil), dealing with the dynamics of personality L ...
s require less energy; children and physically active people require more. Recommendations in the United States are for men and women (respectively) between 31 and 35, at a physical activity level equivalent to walking about per day at in addition to the light physical activity associated with typical day-to-day life,http://health.gov/dietaryguidelines/2015/guidelines/appendix-2/ with guidance suggesting roughly the same levels. Recognizing that people of different age and gender groups have varying daily activity levels, Australia's
National Health and Medical Research Council The National Health and Medical Research Council (NHMRC) is a statutory authority and the primary agency of the Australian Government The Australian Government, also known as the Commonwealth Government, is the national government of Aust ...
recommends no single daily energy intake, but instead prescribes an appropriate recommendation for each age and gender group. Notwithstanding, nutrition labels on Australian food products typically recommend the average daily energy intake of . According to the
Food and Agriculture Organization The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a list of specialized ...
of the
United Nations The United Nations (UN) is an intergovernmental organization An intergovernmental organization (IGO) is an organization composed primarily of sovereign states (referred to as ''member states''), or of other organizations through formal ...

United Nations
, the average minimum energy requirement per person per day is about .


List of countries by food energy intake


Energy usage in the human body

The human body uses the energy released by respiration for a wide range of purposes: about 20% of the energy is used for brain metabolism, and much of the rest is used for the basal metabolic requirements of other organs and tissues. In cold environments, metabolism may increase simply to produce heat to maintain body temperature. Among the diverse uses for energy, one is the production of mechanical energy by skeletal muscle to maintain posture and produce motion. The conversion efficiency of energy from respiration into mechanical (physical)
power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, p ...
depends on the type of food and on the type of physical energy usage (e.g., which muscles are used, whether the muscle is used or ). In general, the efficiency of muscles is rather low: only 18 to 26% of the energy available from respiration is converted into mechanical energy.Stephen Seiler
Efficiency, Economy and Endurance Performance
(1996, 2005).
This low efficiency is the result of about 40% efficiency of generating
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
from the respiration of food, losses in converting energy from ATP into mechanical work inside the muscle, and mechanical losses inside the body. The latter two losses are dependent on the type of exercise and the type of muscle fibers being used (fast-twitch or slow-twitch). However, alterations in the structure of the material consumed can cause modifications in the amount of energy that can be derived from the food; i.e. caloric value depends on the surface area and volume of a food. For an overall efficiency of 20%, one watt of mechanical power is equivalent to . For example, a manufacturer of rowing equipment shows calories released from "burning" food as four times the actual mechanical work, plus per hour, which amounts to about 20% efficiency at 250 watts of mechanical output. It can take up to 20 hours of little physical output (e.g., walking) to "burn off" more than a body would otherwise consume. For reference, each kilogram of body fat is roughly equivalent to 32,300 kilojoules of food energy (i.e., ). In addition, the quality of calories matters because the energy absorption rate of different foods with equal amounts of calories may vary. Some nutrients have regulatory roles affected by
cell signaling 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 mechanisms ...
, in addition to providing energy for the body. For example,
leucine Leucine (symbol Leu or L) is an essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional gro ...

leucine
plays an important role in the regulation of protein metabolism and suppresses an individual's appetite.Garlick, P. J. The role of leucine in the regulation of protein metabolism. Journal of Nutrition, 2005. 135(6): 1553S–6S. Swings in body temperature – either hotter or cooler – increase the metabolic rate, thus burning more energy. Prolonged exposure to extremely warm or very cold environments increases the basal metabolic rate (BMR). People who live in these types of settings often have BMRs 5–20% higher than those in other climates. Physical activity also significantly increases body temperature, which in turn uses more energy from respiration.


See also

* Atwater system * Basal metabolic rate *
Calorie The calorie is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a di ...
*
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 having volume. All everyday objects th ...
*
Food chain A food chain is a linear network of links in a food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is Consumer-resource sy ...

Food chain
*
Food compositionFood composition data (FCD) are detailed sets of information on the nutritionally important components of foods and provide values for energy and nutrients including protein, carbohydrates, fat, vitamins and minerals and for other important food comp ...
*
Heat of combustion The heating value (or energy value or calorific value) of 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 composi ...
*
Nutrition facts label The nutrition facts label (also known as the nutrition information panel, and other slight variations) is a label required on most packaged food in many countries, showing what nutrients (to limit and get enough of) are in the food. Labels are usua ...
*
Table of food nutrientsThe tables below include tabular lists for selected basic foods, compiled from United States Dept. of Agriculture (USDA The United States Department of Agriculture (USDA), also known as the Agriculture Department, is the federal executive depar ...


Footnotes


References


External links


FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors

Is a calorie a calorie?
{{DEFAULTSORT:Food Energy Nutrition