Energy requirements for a human per day[edit]

Suggestion for someone expert in this area: Please do include either a link or content regarding amount of energy consumed by human for different activities (average values) like exercising, studying (mental work), etc.

I've just been trying to find this very thing, this seem to be an area where Wikipedia is still lacking. I have a marginal answer from a BBC schools science program - that people use some 10,000 joules per day. But doing the calculation 10 KJ per day comes out at an average of only 0.12 Watts (J/s) which seems ridiculously low. Trying kilo joules instead of joules gives a power consumption of 120 Watts which now seems just to high. Help please.
By the way - the program also gave an energy consumption for Arctic exploration on foot of 27,000 joules per day. - Lucien86 (talk) 07:22, 15 February 2008 (UTC)[reply]
Further investigation shows that average energy consumption is 10 Mega Joules per day. In the end it was simple - the male standard average calorie intake = 2500 kcal / day, which equals (x4184) 10460000 joules. If you convert it to seconds you get average power consumption - 121 Watts.
Another scale I have is about burning calories; lying down burns about 25 kcal/h, sitting burns 50 kcal/h, standing burns about 80 to 100 kcal/h, walking about 120 kcal/h, and exercise from 150 kcal/h medium to about 300 kcal/h hard. I got the list from a friend I think the numbers originally came from Weight Watchers.
Lucien86 (talk) 14:45, 15 February 2008 (UTC)[reply]


120 W is a standard value for a person used for calculating load on a climate control system. (http://www.inive.org/members_area/medias/pdf/Inive%5Cclima2000%5C1997%5CP291.pdf). --71.252.183.97 (talk) 13:52, 8 August 2008 (UTC)[reply]

The text mentions that "The recommended daily energy intake for young adults and men is 2500 kcal (10 MJ) and 2000 kcal (8 MJ) for women." What's the meaning of this "recommended"? Recommended by who? Shouldn't there be a reference to the source? There are quite a number of them and the figures are somehow conflicting, so this may need a clarification. For instance: "Recommended Dietary Allowances (RDAs) for energy for adult males and females are 3100 and 2400 kcal/day, respectively, but these amounts are generally exceeded by active competitive athletes, though not necessarily by recreational athletes.", Sports nutrition : fats and proteins / [edited by] Judy A. Driskell, 2007.--Rigonz (talk) 04:03, 16 September 2011 (UTC)[reply]


Conflicting Information[edit]

This article contains two separate conflicting descriptions on how the amount of energy in food is measured. one states:

"The food being measured is completely burned in a calorimeter so that the heat released through combustion can be accurately measured. This amount is used to determine the gross energy value of the particular food. This number is then multiplied by a coefficient which is based on how the human body actually digests the food."

the other:

"The amount of food energy in a particular food could be measured by completely burning the dried food in a bomb calorimeter, a method known as direct calorimetry [1]. However, the values given on food labels are not determined this way, because it overestimates the amount of energy that the human digestive system can extract, by also burning dietary fiber. Instead, standardized chemical tests and an analysis of the recipe are used to estimate the product's digestible constituents (protein, carbohydrate, fat, etc.). These results are then converted into an equivalent energy value based on a standardized table of energy densities"

so which is it?

  1. 2 Question after reading all this academic professionally written poetry having one question in mind which is not answered I will post it on one of my blogs since Wikipedia is a great place for mediocre academics legalism grammar experts and other forms of what is insufficient. If you care to ask maybe I will relate it to you but first I will write it up as copyrighted material.--Andrew Zito 06:33, 26 December 2006 (UTC)[reply]
Different countries use different approaches. In the US researchers chemically separate the different kinds of "Macronutrients" and measure the amount contained in the food. The USDA, WHO, and other agencies have developed approximations for the proportion of each nutrient that is normally absorbed by a healthy human (organized by age range). The agencies have also developed useful approximations of the energy available in each gram of a nutrient. An approximation is then used by combining these (4 kcal/g from protein, 4 kcal/g from digestible carbohydrates, 9 kcal/g from protein), and so on). In the US, soluble and insoluble fiber are not distinguished on most food labels but can be found for simple nutrients by web search (insoluble fiber contributes less than 0.2 kcal/g, while soluble fiber contributes about 2 kcal/g). Food manufacturers then use the nutritional information for each basic food in their recipe to estimate the nutrients in their food and the kcal in each serving. Manufacturers often limit their nutritional estimates to ingredients that are over 2% of the total mass of the recipe. The USDA tables include thousands of basic foods and over ten thousand common manufactured foods that have been laboratory analyzed for accurate nutrient content (this information is shared by and added to by most industrialized nations). Drbits (talk) 12:57, 10 August 2016 (UTC)[reply]

calorie/Calorie[edit]

Just as a note, 'calorie' (lowercase c) is used as the equivalent of 4.18 joules, while 'Calorie' (uppercase C) is used as an alternative to 'kilocalorie,' or 4.18 kilojoules. It would be nice if some of the usages in this article were corrected. (Calories, aka kilocalories, are the same units used on food labels, if that helps clarify.) --T. S. Rice 03:21, 13 May 2006 (UTC)[reply]

Never mind, took care of it myself. --T. S. Rice 01:43, 16 May 2006 (UTC)[reply]
That's not a convention generally followed. Gene Nygaard 18:07, 14 September 2006 (UTC)[reply]
Ouch this is totally non standard - heres a joke look it up in the Wikipedia section on calories, the 'calorie' is the conventional name for the 'big calorie' or 'kcal' - 4184 joules. Lucien86 (talk) 14:57, 15 February 2008 (UTC)[reply]

digestion coefficient[edit]

Just wondering if there was any possibility to find the digestion coefficient for proteins and fats... according to this bodybuilding site "It takes about five to six times more energy to process protein than it does carbs." http://www.bullz-eye.com/furci/2001/072701.htm ,under Macro nutrition/protein, 4th paragraf... However, I don't know how legitimate these claims are.

Burn the energy[edit]

Wouldnt it be good to add information about how much physical exercise you need to get rid of the energy? Well, maybe this isn't the right article to add this info, I don't know. Though I'd really like to know and I can't find it anywhere, so is it possible to add? Thx Cybesystem 19:18, 18 January 2007 (UTC)[reply]

Try googling for "calories burned" for some nice tables of activities. Inhumandecency 09:13, 30 June 2007 (UTC)[reply]

Fat creation and Calories[edit]

Human fat is created when excess blood sugar is converted to fat by insulin -- this is very important to diabetics who don't produce enough insulin. Grain alcohol does not increase blood sugar, so it's not readily available as energy, and it can't be directly converted to fat. Other foods are digested slowly enough that the sugars are released slowly in the blood stream and are used, rather than converted to human fat. So burning alcohol (or other foods) in a test device to measure heat given off is really not a very reliable indication of whether you will gain weight in the form of fat. It may be relatively accurate for some foods, but totally inaccurate for others, like pure grain alcohol. I would like to see more comments on better ways to officially measure the energy value of food than using calories as a measurement. Glycemic index is one--why isn't it used? Rickhan 17:23, 3 July 2007 (UTC).[reply]

serving size[edit]

The article currently states: "The energy content of food is usually given on labels for 100 g and/or for what the manufacturer claims is a typical serving size." However, at least in the United States, the serving size is regulated by the government (in 21 CFR 101.9(b) and 21 CFR 101.12), not by the manufacturer. I can't come up with a concise rewriting of this sentence to express this... Can anyone else?

Perhaps more sentences are needed. In the UK (possibly the EU too), it is law that the "per 100g/ml" amounts must be displayed, but the manufacturer can state a separate serving size too.

More calorie confusion[edit]

This article uses the figure of 4.1868 J/cal instead of 4.184 J/cal. The former is given as the international steam table calorie and the latter is the more commonly used thermochemical standard. What references/proof is there that the steam table value is the correct value used for food? Is there a USDA reference?

Also: what is the G.E.V mentioned in the measuring section? It is not previously mentioned, and it is not defined later in the article.

Heat calories[edit]

How much of an effect does the temperature of the food have? If you eat warm food, you don't need to expend chemical energy warming yourself. 71.167.69.224 (talk) 15:18, 15 June 2008 (UTC)[reply]

True, but unless you are cold, you don't need the extra heat. If you assume all food has about the same heat capacity as water, from this article you can derive the equivalent "food energy" value of a given weight of food eaten at a given temperature. --Una Smith (talk) 23:19, 17 December 2008 (UTC)[reply]
The temperature of the food is more or less irrelevant. Drinking an entire liter of water at 0 degrees Celsius would burn 37,000 calories or 37 Cal/kcal. That's obviously a very small amount compared to 2,000 Cal/kcal daily, and inaccuracies measuring food, exercise, or even a slight change in metabolism will all have much larger effects on your net caloric intake. — Preceding unsigned comment added by 2600:1700:CF0:EE50:7079:B205:CF92:D52C (talk) 02:32, 28 January 2020 (UTC)[reply]

Energy usage in the human body[edit]

This section assumes 30% digestion efficiency (by citing an article about digestion efficiency in insects). I suspect two things wrong with this:

  1. The digestion efficiency is already accounted for in our measurement of nutritional calories (as discussed in the introduction to this article).
  2. The 30% figure is not mentioned anywhere in the cited article as being appropriate to a human, nor even a general vertebrate. It is the value for a chicken fed on grain.

If this is true, then the example calculation should be much more straightforward: ΔW (lbs) ≈ Econsumed - Eexpended (kcal) × (1 lb / 4000 kcal)
--71.252.183.97 (talk) 14:12, 8 August 2008 (UTC)[reply]


Absolutely wrong. If you absorbed all the energy in food then why do you have excreta? Don't oversimplify. —Preceding unsigned comment added by 144.223.18.102 (talk) 18:16, 23 April 2009 (UTC)[reply]
He wasn't wrong. The energy not used becasue of excretia is already taken into account when they calculate the calories in food. So a candy bar of 100 Cal is actually more like 130 Cal, but 30 Cal is not absorbed.YobMod 12:42, 30 July 2009 (UTC)[reply]

The writing style[edit]

is awful —Preceding unsigned comment added by 71.196.156.144 (talk) 00:08, 21 October 2008 (UTC)[reply]

Burning calories does not directly reduce mass[edit]

There is much confusion in this article and in the population in general regarding the conservation of mass. "Burning" calories does not cause weight loss. There is no one-to-one correspondence between calorie expenditure and mass depreciation. Like any chemical reaction, extracting energy out of caloric sources does not alter the mass of the fuel. Only through excretion does mass depart a body. ---Ransom (--69.105.94.38 (talk) 06:17, 7 December 2008 (UTC))[reply]

Flat out wrong. Burning stuff, like fat, reduces its mass. You are exhaling most of the combustion products, CO2 and water, through breath and urine. —Preceding unsigned comment added by 207.34.120.71 (talk) 17:14, 13 January 2009 (UTC)[reply]

conversion of cal/g to kJ/g[edit]

Someone care to attempt creating the following templates? 0 calories per gram (0 kJ/g) & 0 kilocalories per gram (0 kJ/g) Peter Horn 00:42, 20 March 2009 (UTC)[reply]

Dubious tag[edit]

I added a tag to this:

"Only carbohydrates (including fiber), fats, proteins, organic acids, polyols, and ethanol contain food energy."

I understand what it is trying to say, but it is simply not true. It sounds like something a nutritionist would say, so while being a useful guide for layman, but as a biochemist i know that other organic chemicals can be ingested and are metabolised to give energy. Ethanol is only singled out as it is legally sold to drink, but methanol, propanol, butanol, ketones, aldehdyes, amines, esters, etc can all also be metabolised, and some are less toxic than ethanol, and are common ingredients in foods.

This does not even approach the claim that spices have no energy. The only difference between parpika the spice and a pepper is the drying. Clearly peppers have caloires, and so does chilli powder.

Also, where did the definition of food being something with one of the allowed ingredients come from? Very many foods are available that claim no calories. I don't think anyone defines these as "not food" all because they do not provide calories. They are certainly foods for tax purposes.YobMod 12:30, 30 July 2009 (UTC)[reply]

How about ..."contain a significant amount of food energy"? Does that work?--chaser (talk) 20:02, 16 September 2009 (UTC)[reply]

kWh[edit]

The kWh calculation should also be mentioned. 2000 calories = 2,3 kWh see http://www.manicore.com/anglais/documentation_a/slaves.html Comes in handy when comparing robots energy expenditure to men, and for other uses

add to article —Preceding unsigned comment added by 81.243.178.120 (talk) 06:14, 14 August 2009 (UTC)[reply]

Food energy is the amount of energy obtained from food..[edit]

A definition is not really a definition if it only refers to itself. Children make statements of this sort, encyclopedias do not.Nickrz (talk) 21:29, 13 April 2011 (UTC)[reply]

I think you mean that the text uses a circular definition. However, this is not the case. For example, the energy in cellulose is approximately 4 kcal/gram, but the energy obtained by humans from cellulose is close to 0. Mammalian digestive systems do not contain enzymes to break cellulose into a form that the body can absorb. However, there are bacteria that release enzymes to break down cellulose. In the human digestive system, most of the resulting sugar is absorbed by bacteria and the bacteria are excreted. Ruminants regurgitate (into their mouths) cellulose and the bacteria that helps break it down. By chewing this "cud" the bacteria are exposed to more of the cellulose and the resulting bacteria can be digested.
Dietitians distinguish between soluble fiber and insoluble fiber (such as cellulose). Soluble fiber disperses in water and bacteria have easy access to it in the human colon (a healthy adult human colon contains over 2000 species of bacteria). About half of the energy in soluble fiber is normally absorbed by humans. Drbits (talk) 12:24, 10 August 2016 (UTC)[reply]

Calorie = 1000 calories ?[edit]

Whoever has designed this naming system has blundered. This is so errorprone. Pronounciation is same for both "calories". How do we know which is which ? — Preceding unsigned comment added by Vwalvekar (talk • contribs) 17:23, 30 November 2012 (UTC)[reply]

This is an old problem that can no longer be fixed, as it would confuse over 500 million people. The calorie is a metric measure. Grocers and others in the US decided that writing that a slice of bread is 80,000 calories was too cumbersome (and it implies too much precision), so they started using Calories (which are actually kilocalories). Kilocalories (Calories) or kilojoules are always used for food, while "calories" is considered archaic (scientists in the US and most other countries use joules and newtons). Dieticians and the US government have begun to use kJoules or kcal instead of Calories. In countries that have converted completely to the metric system, Joules and Kilojoules are usually used. Drbits (talk) 12:05, 10 August 2016 (UTC)[reply]

EU law[edit]

"In the European Union, manufacturers of packaged food must label the nutritional energy of their products in both kilocalories and kilojoules," This is wrong only joule is a requirement, calorie are only tolerated. EEC/EU even tried to prohibit the calorie as early as the 1970's (71/354/EEC chapter III). If memory servers me, it was the US who lobbied for the calorie, making is easier for US manufactures to export to Europe.94.145.236.194 (talk) 14:56, 31 May 2013 (UTC)[reply]

have you any valid source?--Bolzanobozen (talk) 15:23, 27 August 2017 (UTC)[reply]

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Environmental Impact of Animal Products Table[edit]

Why is this here? This article isn't about animal products in particular, or environmentalism, or veganism. Is there any reason at all to include it? — Preceding unsigned comment added by 2600:1700:CF0:EE50:7079:B205:CF92:D52C (talk) 02:17, 28 January 2020 (UTC)[reply]

 Done - agree it was irrelevant and is now removed. Thanks. --Zefr (talk) 02:21, 28 January 2020 (UTC)[reply]

Quibble on "energy density"[edit]

I removed the following sentence since it seemed to be more confusing than illuminating to the readers:

However "energy density" is a misleading term ((clarify|reason=Correct concept, but highly needlessly pedantic to consider it misleading. We talk about energy density for non-edible fuels too, and like in that case there is a clear (if not stronger) presumption of sufficient oxygen intake.|date=January 2022)) 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.<ref name="Schmidt-Rohr 15" />See for example the Energy section (follow "Fuels") in Science Issues http://scienceissues.org.uk</ref>

It should be obvious that, in this article, "energy content" or "energy density" always refers to the energy that the body can obtain from the food by respirative metabolism, not to some other meaning that the term may have in chemistry or physics. However, for good measure, it seems best to avoid the term "energy density". --Jorge Stolfi (talk) 23:26, 20 January 2022 (UTC)[reply]

Possible "original research"?[edit]

I removed this sentence since it seems to be "original research":

Theoretically, the food energy value could be obtained also by measuring the ATP generated by metabolizing the food.

I wonder whether this is possible, even in theory, given the timing of ATP creation and regeneration, its creation from energy stored in the body etc. --Jorge Stolfi (talk) 23:58, 20 January 2022 (UTC)[reply]

Original research about effect of area and volume of food?[edit]

The following sentence was removed because it was unsourced and appears to be "original research":

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.

There may be some truth hidden in this statement, but given that most food is chewed and digested, down to a molecular level, before respiration actually starts, it does not seem to make much sense as it is. --Jorge Stolfi (talk) 06:10, 21 January 2022 (UTC)[reply]

More original research? Exercise raises body temperature[edit]

I removed this sentence because has long been unsourced and seems to be "original research" and mostly wrong:

Physical activity also significantly increases body temperature, which in turn uses more energy from respiration.[citation needed]

--Jorge Stolfi (talk) 06:43, 21 January 2022 (UTC)[reply]

More original research? Effect of ambient temperature on basal metabolism rate[edit]

I removed the following sentences because they have been unsourced for a long time, and may be either "original research" or unproven "folklore":

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.[citation needed]

It seems well-established and logical that that lowering the ambient temperature below the "room" values causes an almost immediate increase in metabolism rate, both at rest and under exercise, as the body needs to expend extra energy in order to keep the internal temperature at the normal level. But there are several sources on the internet claiming that high enough ambient temperatures also cause an increase in metabolism, either at rest or under exercise, because the body needs to consume more energy to shed internal heat. While this seems at least possible, intuitively, I could not find any reports of this effect having been measured. Anyway, those internet sources do not specify the ambient temperature at which the effect starts (that is, the ambient temp that minimizes the BMR or exercise MR). The claim above, that hot climates have this effect, also are unsourced and dubious. --Jorge Stolfi (talk) 08:48, 21 January 2022 (UTC)[reply]

Wiki Education assignment: Medical missionaries to Community Partners[edit]

This article was the subject of a Wiki Education Foundation-supported course assignment, between 30 August 2023 and 12 January 2024. Further details are available on the course page. Student editor(s): Jnguyen7 (article contribs).

— Assignment last updated by Remy.2005 (talk) 18:46, 4 February 2024 (UTC)[reply]

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