Food energy
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Food energy is
chemical energy Chemical energy is the potential of a 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 object ...
that animals (including
human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only Extant taxon, ...

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, vit ...

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 with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
from air with the
molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms held together by chemical bo ...

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-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cellu ...

metabolism
and to drive their muscles. Foods are composed chiefly of
carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) ato ...
s,
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 individual contiguous system that embodies ...

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 Nobe ...
,
water Water (chemical formula H2O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts ...

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 and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (20 ...
. 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 organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO2OH, are ...
s,
polyolA polyol is an organic compound containing multiple hydroxyl (HO− Radical (chemistry), radical) groups. The term "polyol" can have slightly different meanings depending on whether it is being used in the field of food science or that of polymer che ...
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), o ...

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 (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: life, ...
s can extract food energy from the respiration of
cellulose Cellulose 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 and ...

cellulose
because of
bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a Bacte ...

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 International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * International (Kevin Michael album), ''International'' (Kevin Michael album), 2011 * International (New Order album), '' ...
, researchers measure energy in
joule 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 ...

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 system of measurement A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes ...

metric system
unit of energy, still widely used in food-related contexts, is the
calorie 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 ...
; more precisely, the "food calorie", "large calorie" or
kilocalorie The calorie is a unit of energy defined as the amount of heat needed to raise the temperature of a quantity of water by one degree. For historical reasons, two main definitions of calorie are in wide use. The small calorie or gram calorie (usua ...
(kcal or Cal), equal to 4.184 kilojoules. Within the
European Union The European Union (EU) is a political and economic union of Member state of the European Union, member states that are located primarily in Europe. Its members have a combined area of and an estimated total population of about 447million ...

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 (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through S ...

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 formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three comm ...

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, radiation, and physical properties of matter. The behavior of these quantities is governe ...
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 Calorimeter#Bomb calorimeters, bomb calorimeter and corrections that take into consideration the efficiency of digestion and absorption and the production of urea and other substances in the urine. The American chemist Wilbur Atwater 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

Image:Nutrition-label.jpg, 220px, The nutritional information label on a pack of Basmati rice in the United Kingdom Many governments Mandatory labelling, 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 calorimeter, bomb calorimeter, a method known as direct calorimetry. 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, 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,
carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) ato ...
,
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 individual contiguous system that embodies ...

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 Brain#Metabolism, brain energy consumption.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 lifestyles 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 France, French 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 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 of the 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 (physics), power 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 Aerobic exercise, aerobically or Anaerobic exercise, anaerobically). 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 Adenosine triphosphate, 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 addition to providing energy for the body. For example, 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 * Chemical energy * Food chain * Food composition * Heat of combustion#Heating value, Heat of combustion * Nutrition facts label *Table of food nutrients


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