Editing Food energy (section)

== Dietary sources of energy ==
The typical human [[diet (nutrition)|diet]] consists chiefly of carbohydrates, fats, proteins, water, ethanol, and indigestible components such as [[bone]]s, [[seed]]s, and fibre (mostly [[cellulose]]). Carbohydrates, fats, and proteins typically comprise ninety percent of the dry weight of food.<ref>{{cite web|url= http://www.merck.com/mmhe/sec12/ch152/ch152b.html |title=Carbohydrates, Proteins, Nutrition|work=  The Merck Manual}}</ref> [[Ruminant]]s can extract food energy from the respiration of cellulose because of [[bacteria]] in their [[rumen]]s 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 acid|citric]] and [[tartaric acid|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.<ref name=jeff2006/> For example, [[leucine]] plays an important role in the regulation of protein metabolism and suppresses an individual's appetite.<ref name=garl2005/>  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<ref name=EUtab1990/> and UK regulations,<ref name=UKSI1996/> are:
{| class="wikitable"
|-
! rowspan=2 | Food component
! colspan=2 | [[Specific energy#Energy density of food|Energy density]]
|-
! kJ/g
! kcal/g
|-
| [[Fat]]
| align=center|37
| align=center|9
|-
| [[Ethanol]]
| align=center|29
| align=center|7
|-
| [[Protein (nutrient)|Protein]]s
| align=center|17
| align=center|4
|-
| [[Carbohydrate]]s
| align=center|17
| align=center|4
|-
| [[Organic acid]]s
| align=center|13
| align=center|3
|-
| [[Polyol]]s ([[sugar alcohol]]s, [[sweeteners]]) (1)
| align=center|10
| align=center|2.4
|-
| [[dietary fiber|Fiber]] (2)
| align=center|8
| align=center|2
|}

(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,<ref name=EUtab1990/> but not in the UK regulations, according to which fibre shall not be counted.<ref name=UKSI1996/>

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.<ref name=FAO2003/>

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