Food energy

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Food energy is chemical energy that animals (including humans) derive from their food to sustain their metabolism, including their muscular activity. [1]

Contents

Most animals derive most of their energy from aerobic respiration, namely combining the carbohydrates, fats, and proteins with oxygen from air or dissolved in water. [2] Other smaller components of the diet, such as organic acids, polyols, and ethanol (drinking alcohol) may contribute to the energy input. Some diet 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. Some organisms have instead anaerobic respiration, which extracts energy from food by reactions that do not require oxygen.

The energy contents of a given mass of food is usually expressed in the metric (SI) unit of energy, the joule (J), and its multiple the kilojoule (kJ); or in the traditional unit of heat energy, the calorie (cal). In nutritional contexts, the latter is often (especially in US) the "large" variant of the unit, also written "Calorie" (with symbol Cal, both with capital "C") or "kilocalorie" (kcal), and equivalent to 4184 J or 4.184 kJ. [3] Thus, for example, fats and ethanol have the greatest amount of food energy per unit mass, 37 and 29 kJ/g (9 and 7 kcal/g), respectively. Proteins and most carbohydrates have about 17 kJ/g (4 kcal/g), though there are differences between different kinds. For example, the values for glucose, sucrose, and starch are 15.57, 16.48 and 17.48 kilojoules per gram (3.72, 3.94 and 4.18 kcal/g) respectively. The differing energy density of foods (fat, alcohols, carbohydrates and proteins) lies mainly in their varying proportions of carbon, hydrogen, and oxygen atoms. Carbohydrates that are not easily absorbed, such as fibre, or lactose in lactose-intolerant individuals, contribute less food energy. Polyols (including sugar alcohols) and organic acids contribute 10 kJ/g (2.4 kcal/g) and 13 kJ/g (3.1 kcal/g) respectively. [4]

The energy contents of a complex dish or meal can be approximated by adding the energy contents of its components.

History and methods of measurement

Direct calorimetry of combustion

The first determinations of the energy content of food were made by burning a dried sample in a bomb calorimeter and measuring the temperature change in the water surrounding the apparatus, a method known as direct calorimetry. [5]

The Atwater system

However, the direct calorimetric method generally overestimates the actual energy that the body can obtain from the food, because it also counts the energy contents of dietary fiber and other indigestible components, and does not allow for partial absorption and/or incomplete metabolism of certain substances. For this reason, today the energy content of food is instead obtained indirectly, by using chemical analysis to determine the amount of each digestible dietary component (such as protein, carbohydrates, and fats), and adding the respective food energy contents, previously obtained by measurement of metabolic heat released by the body. [6] [7] In particular, the fibre content is excluded. This method is known as the Modified Atwater system, after Wilbur Atwater who pioneered these measurements in the late 19th century. [1] [8]

The system was later improved by Annabel Merrill and Bernice Watt of the USDA, who derived a system whereby specific calorie conversion factors for different foods were proposed. [9]

Dietary sources of energy

The typical human diet consists chiefly of carbohydrates, fats, proteins, water, ethanol, and indigestible components such as bones, seeds, and fibre (mostly cellulose). Carbohydrates, fats, and proteins typically comprise ninety percent of the dry weight of food. [10] Ruminants can extract food energy from the respiration of cellulose because of bacteria in their rumens that decompose it into digestible carbohydrates.

Other minor components of the human diet that contribute to its energy content are organic acids such as citric and tartaric, and polyols such as glycerol, xylitol, inositol, and sorbitol.

Some nutrients have regulatory roles affected by cell signaling, in addition to providing energy for the body. [11] For example, leucine plays an important role in the regulation of protein metabolism and suppresses an individual's appetite. [12] Small amounts of essential fatty acids, constituents of some fats that cannot be synthesized by the human body, are used (and necessary) for other biochemical processes.

The approximate food energy contents of various human diet components, to be used in package labeling according to the EU regulations [13] and UK regulations, [14] are:

Food component Energy density
kJ/gkcal/g
Fat 379
Ethanol 297
Proteins 174
Carbohydrates 174
Organic acids 133
Polyols (sugar alcohols, sweeteners) (1)102.4
Fiber (2)82

(1) Some polyols, like erythritol, are not digested and should be excluded from the count.

(2) This entry exists in the EU regulations of 2008, [13] but not in the UK regulations, according to which fibre shall not be counted. [14]

More detailed tables for specific foods have been published by many organizations, such as the United Nations Food and Agriculture Organization also has published a similar table. [3]

Other components of the human diet are either noncaloric, or are usually consumed in such small amounts that they can be neglected.

Energy usage in the human body

The food energy actually obtained by respiration is used by the human body for a wide range of purposes, including basal metabolism of various organs and tissues, maintaining the internal body temperature, and exerting muscular force to maintain posture and produce motion. About 20% is used for brain metabolism. [3]

The conversion efficiency of energy from respiration into muscular (physical) 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 aerobically or 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. [15] This low efficiency is the result of about 40% efficiency of generating 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). For an overall efficiency of 20%, one watt of mechanical power is equivalent to 18 kJ/h (4.3 kcal/h). For example, a manufacturer of rowing equipment shows calories released from "burning" food as four times the actual mechanical work, plus 1,300 kJ (300 kcal) per hour, [16] 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" 17,000 kJ (4,000 kcal) [17] 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., 3,500 kilocalories per pound or 7,700 kilocalories per kilogram). [18]

Many countries and health organizations have published recommendations for healthy levels of daily intake of food energy. For example, the United States government estimates 8,400 and 10,900 kJ (2,000 and 2,600 kcal) needed for women and men, respectively, between ages 26 and 45, whose total physical activity is equivalent to walking around 2.5 to 5 km (1+1⁄2 to 3 mi) per day in addition to the activities of sedentary living. These estimates are for a "reference woman" who is 1.63 m (5 ft 4 in) tall and weighs 57 kg (126 lb) and a "reference man" who is 1.78 m (5 ft 10 in) tall and weighs 70 kg (154 lb). [19] Because caloric requirements vary by height, activity, age, pregnancy status, and other factors, the USDA created the DRI Calculator for Healthcare Professionals in order to determine individual caloric needs. [20] [21]

According to the Food and Agriculture Organization of the United Nations, the average minimum energy requirement per person per day is about 7,500 kJ (1,800 kcal). [22] Although the U.S. has changed over time with a growth in population and processed foods or food in general, Americans today have available roughly the same level of calories as the older generation.

Older people and those with sedentary lifestyles require less energy; children and physically active people require more. Recognizing these factors, Australia's National Health and Medical Research Council recommends different daily energy intakes for each age and gender group. [23] Notwithstanding, nutrition labels on Australian food products typically recommend the average daily energy intake of 8,800 kJ (2,100 kcal).

The minimum food energy intake is also higher in cold environments. Increased mental activity has been linked with moderately increased brain energy consumption. [24]

Nutrition labels

The nutritional information label on a pack of Basmati rice in the United Kingdom Nutrition-label.jpg
The nutritional information label on a pack of Basmati rice in the United Kingdom

Many governments require food manufacturers to label the energy content of their products, to help consumers control their energy intake. To facilitate evaluation by consumers, food energy values (and other nutritional properties) in package labels or tables are often quoted for convenient amounts of the food, rather than per gram or kilogram; such as in "calories per serving" or "kcal per 100 g", or "kJ per package". The units vary depending on country:

CountryMandatory unit (symbol)Second unit (symbol)Common usage
United States Calorie (Cal) [25] kilojoule (kJ), optional [25] calorie (cal) [26]
Canada Calorie (Cal) [ citation needed ]kilojoule (kJ), optional [ citation needed ]calorie (cal) [ citation needed ]
Australia and New Zealand kilojoule (kJ) [27] [28] kilocalorie (kcal), optional [27] [28] AU: kilocalorie (kcal) [ citation needed ]
United Kingdom kJ [14] kcal, mandatory [14]
European Union kilojoule (kJ) [29] kilocalorie (kcal), mandatory [29]
Brazil caloria or quilocaloria (kcal) [30] caloria

See also

Related Research Articles

<span class="mw-page-title-main">Carbohydrate</span> Organic compound that consists only of carbon, hydrogen, and oxygen

A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 and thus with the empirical formula Cm(H2O)n, which does not mean the H has covalent bonds with O. However, not all carbohydrates conform to this precise stoichiometric definition, nor are all chemicals that do conform to this definition automatically classified as carbohydrates.

<span class="mw-page-title-main">Calorie</span> Unit of energy used in nutrition

The calorie is a unit of energy that originated from the obsolete caloric theory of heat. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, dietary calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius. The small calorie or gram calorie was defined as the amount of heat needed to cause the same increase in one gram of water. Thus, 1 large calorie is equal to 1000 small calories.

<span class="mw-page-title-main">Fat</span> Esters of fatty acid or triglycerides

In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food.

A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products, leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.

<span class="mw-page-title-main">Human nutrition</span> Provision of essential nutrients necessary to support human life and health

Human nutrition deals with the provision of essential nutrients in food that are necessary to support human life and good health. Poor nutrition is a chronic problem often linked to poverty, food security, or a poor understanding of nutritional requirements. Malnutrition and its consequences are large contributors to deaths, physical deformities, and disabilities worldwide. Good nutrition is necessary for children to grow physically and mentally, and for normal human biological development.

<span class="mw-page-title-main">Low-carbohydrate diet</span> Diets restricting carbohydrate consumption

Low-carbohydrate diets restrict carbohydrate consumption relative to the average diet. Foods high in carbohydrates are limited, and replaced with foods containing a higher percentage of fat and protein, as well as low carbohydrate foods.

Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.

<span class="mw-page-title-main">Cat food</span> Food for consumption by cats

Cat food is food specifically designed for consumption by cats. As obligate carnivores, cats have specific requirements for their dietary nutrients, namely nutrients found only in meat, such as taurine, arginine, and Vitamin B6. Certain nutrients, including many vitamins and amino acids, are degraded by the temperatures, pressures and chemical treatments used during manufacture, and hence must be added after manufacture to avoid nutritional deficiency.

Resting metabolic rate (RMR) is whole-body mammal metabolism during a time period of strict and steady resting conditions that are defined by a combination of assumptions of physiological homeostasis and biological equilibrium. RMR differs from basal metabolic rate (BMR) because BMR measurements must meet total physiological equilibrium whereas RMR conditions of measurement can be altered and defined by the contextual limitations. Therefore, BMR is measured in the elusive "perfect" steady state, whereas RMR measurement is more accessible and thus, represents most, if not all measurements or estimates of daily energy expenditure.

Specific dynamic action (SDA), also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage. Heat production by brown adipose tissue which is activated after consumption of a meal is an additional component of dietary induced thermogenesis. The thermic effect of food is one of the components of metabolism along with resting metabolic rate and the exercise component. A commonly used estimate of the thermic effect of food is about 10% of one's caloric intake, though the effect varies substantially for different food components. For example, dietary fat is very easy to process and has very little thermic effect, while protein is hard to process and has a much larger thermic effect.

Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.

<span class="mw-page-title-main">Nutrition facts label</span> Table of nutrition facts on food labels

The nutrition facts label is a label required on most packaged food in many countries, showing what nutrients and other ingredients are in the food. Labels are usually based on official nutritional rating systems. Most countries also release overall nutrition guides for general educational purposes. In some cases, the guides are based on different dietary targets for various nutrients than the labels on specific foods.

The Atwater system, named after Wilbur Olin Atwater, or derivatives of this system are used for the calculation of the available energy of foods. The system was developed largely from the experimental studies of Atwater and his colleagues in the later part of the 19th century and the early years of the 20th at Wesleyan University in Middletown, Connecticut. Its use has frequently been the cause of dispute, but few alternatives have been proposed. As with the calculation of protein from total nitrogen, the Atwater system is a convention and its limitations can be seen in its derivation.

<span class="mw-page-title-main">Very-low-calorie diet</span> Diet with very or extremely low daily food energy consumption

A very-low-calorie diet (VLCD), also known as semistarvation diet and crash diet, is a type of diet with very or extremely low daily food energy consumption. VLCDs are defined as a diet of 800 kilocalories (3,300 kJ) per day or less. Modern medically supervised VLCDs use total meal replacements, with regulated formulations in Europe and Canada which contain the recommended daily requirements for vitamins, minerals, trace elements, fatty acids, protein and electrolyte balance. Carbohydrates may be entirely absent, or substituted for a portion of the protein; this choice has important metabolic effects. Medically supervised VLCDs have specific therapeutic applications for rapid weight loss, such as in morbid obesity or before a bariatric surgery, using formulated, nutritionally complete liquid meals containing 800 kilocalories or less per day for a maximum of 12 weeks.

<span class="mw-page-title-main">Protein (nutrient)</span> Nutrient for the human body

Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.

Starvation response in animals is a set of adaptive biochemical and physiological changes, triggered by lack of food or extreme weight loss, in which the body seeks to conserve energy by reducing the amount of calories it burns.

<span class="mw-page-title-main">Western pattern diet</span> Modern dietary pattern

The Western pattern diet is a modern dietary pattern that is generally characterized by high intakes of pre-packaged foods, refined grains, red meat, processed meat, high-sugar drinks, candy and sweets, fried foods, industrially produced animal products, butter and other high-fat dairy products, eggs, potatoes, corn, and low intakes of fruits, vegetables, whole grains, pasture-raised animal products, fish, nuts, and seeds.

<span class="mw-page-title-main">Weight management</span> Techniques for maintaining body weight

Weight management refers to behaviors, techniques, and physiological processes that contribute to a person's ability to attain and maintain a healthy weight. Most weight management techniques encompass long-term lifestyle strategies that promote healthy eating and daily physical activity. Moreover, weight management involves developing meaningful ways to track weight over time and to identify ideal body weights for different individuals.

<span class="mw-page-title-main">Puppy nutrition</span>

The developmental life stage of dogs requires a specific intake of nutrients to ensure proper growth and development and to meet energy requirements. Despite the fact that puppies have different nutritional requirements compared to their adult counterparts, of the 652 breeders surveyed in the United States and Canada in 2012, 8.7% report feeding puppies commercial diets not intended for the developmental life stage of canines. Large and small dog breeds have even more specific nutrient requirements during growth, such as adjusted calcium to phosphorus ratio, and as such should receive a breed specific growth formula. Feeding diets formulated by a nutritionist for specific breeds and life stage differences in nutrient requirements ensures a growing puppy will receive the proper nutrition associated with appropriate skeletal, neurological and immune development. This includes nutrients such as protein, fibre, essential fatty acids, calcium and vitamin E. It is therefore important to feed puppies a diet that meets the minimum and/or maximum requirements established by the National Research Council.

References

  1. 1 2 Allison Marsh (2020): "How Counting Calories Became a Science: Calorimeters defined the nutritional value of food and the output of steam generators Archived 2022-01-21 at the Wayback Machine " Online article on the IEEE Spectrum Archived 2022-01-20 at the Wayback Machine website, dated 29 December 2020. Accessed on 2022-01-20.
  2. ↑ Ross, K. A. (2000c) Energy and fuel, in Littledyke M., Ross K. A. and Lakin E. (eds), Science Knowledge and the Environment. London: David Fulton Publishers.
  3. 1 2 3 United Nations Food and Agriculture Organization (2003): "FAO Food and Nutrition Paper 77: Food energy - methods of analysis and conversion factors Archived 2010-05-24 at the Wayback Machine ". Accessed on 21 January 2022.
  4. ↑ "Schedule 7: Nutrition labelling". Legislation.gov.uk. The National Archives. 1 July 1996. Retrieved 13 December 2019.
  5. ↑ Adrienne Youdim (2021): "Calories Archived 2013-08-04 at the Wayback Machine ". Article in the Merck Manual Home Edition online, dated Dec/2011. Accessed on 21 February 2022
  6. ↑ "Nutrient Value of Some Common Foods" (PDF). Health Canada, PDF p. 4. 1997. Retrieved 25 January 2015.
  7. ↑ "How Do Food Manufacturers Calculate the Calorie Count of Packaged Foods?". Scientific American. Retrieved 8 September 2017.
  8. ↑ "Why food labels are wrong" Archived 2011-11-13 at the Wayback Machine by Bijal Trivedi, New Scientist , 18 July 2009, pp. 30-3.
  9. ↑ Annabel Merrill; Bernice Watt (1973). Energy Values of Food ... basis and derivation (PDF). United States Department of Agriculture. Archived from the original (PDF) on 22 November 2016.
  10. ↑ "Carbohydrates, Proteins, Nutrition". The Merck Manual.
  11. ↑ Jeffrey S. F. (2006). "Regulating Energy Balance: The Substrate Strikes Back". Science: 861–864.
  12. ↑ Garlick, P. J. The role of leucine in the regulation of protein metabolism. Journal of Nutrition, 2005. 135(6): 1553S–6S.
  13. 1 2 "Council directive 90/496/EEC of 24 September 1990 on nutrition labelling for foodstuffs". Archived from the original on 3 October 2011. Retrieved 18 March 2010.
  14. 1 2 3 4 United Kingdom The Food Labelling Regulations 1996 Archived 2013-09-21 at the Wayback Machine – Schedule 7: Nutrition labelling Archived 2013-03-17 at the Wayback Machine
  15. ↑ Stephen Seiler, Efficiency, Economy and Endurance Performance Archived 2007-12-21 at the Wayback Machine (1996, 2005).
  16. ↑ Concept II Rowing Ergometer, user manual Archived 2010-12-26 at the Wayback Machine (1993).
  17. ↑ Guyton A. C., Hall J. E. Textbook of medical physiology, 11 ed., p. 887, Elsevier Saunders, 2006.
  18. ↑ Wishnofsky, M. Caloric Equivalents of Gained or Lost Weight. The American Journal of Clinical Nutrition, (1958).
  19. ↑ US National Institutes of Health (2015): "Dietary guidelines Archived 2016-03-01 at the Wayback Machine "
  20. ↑ "Dietary Guidelines for Americans 2020 - 2025" (PDF). dietaryguidelines.gov. USDA & HHS. Retrieved 17 May 2022.
  21. ↑ "DRI Calculator for Healthcare Professionals". usda.gov. U.S. Department of Agriculture. Retrieved 17 May 2022.
  22. ↑ United Nations Food and Agriculture Organization (2014): "Hunger Archived 2009-12-20 at the Wayback Machine ". Accessed on 27 September 2014
  23. ↑ "Dietary Energy" . Retrieved 27 September 2014.
  24. ↑ Evaluation of a mental effort hypothesis for correlations between cortical metabolism and intelligence Archived 2012-10-23 at the Wayback Machine , Intelligence, Volume 21, Number 3, November 1995 , pp. 267-278(12), 1995.
  25. 1 2 United States Federal Government (1977), "Code of Federal Regulations - Part 101 - Food labeling Archived 2022-01-21 at the Wayback Machine ", from Federal Register 14308, 15 March 1977.
  26. ↑ U. S. Food and Drug Administration (2019): "Calories on the Menu - Information for Archived 2022-01-20 at the Wayback Machine ". Online document at the FDA Website Archived 2013-09-15 at the Wayback Machine , dated 5 August 2019. Accessed on 2022-01-20.
  27. 1 2 Health. "Australia New Zealand Food Standards Code – Standard 1.2.8 – Nutrition information requirements". www.legislation.gov.au. Retrieved 29 May 2020.
  28. 1 2 "What's the difference between a calorie and a kilojoule". Queensland Health . 21 February 2017. Retrieved 29 May 2020.
  29. 1 2 European Union Parliament (2011): "Regulation (EU) No 1169/2011 Archived 2022-01-11 at the Wayback Machine " Document 02011R1169-20180101
  30. ↑ Ministério da Saúde, Brazil (2020): "Instrução Normativa Nº 75 - Estabelece os requisitos técnicos para declaração da rotulagem nutricional nos alimentos embalados Archived 2022-01-21 at the Wayback Machine ", dated 2020-10-08, published on Diário Oficial da União on 2020-10-09, page 113.
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