Food energy
Overview
Fats and ethanol have the greatest amount of food energy per gram, 37 and 29 kilojoules per gram (8.8 and 6.9 kcal/g),[citation needed] respectively. Proteins and most carbohydrates both have about 17 kJ/g (4 kcal/g). 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.
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