Energy provided by macronutrients

Energy is needed for essential body functions (such as breathing), growth (especially during childhood), and physical activities (working and playing).

Macronutrients provide different amounts of energy, expressed as kilocalories (Kcals). Fat provides approximately twice as much energy (9 kcals/g) as the same weight of protein or carbohydrate (4 kcal/g). As stated above, more carbohydrate than fat is usually eaten in developing countries and, therefore, most food energy in the diet in these countries is derived from carbohydrate sources.

The relative concentration of protein and fat in the diet is important and is expressed by the percentage of energy in the diet provided by either fat or protein. For example, if a diet provides 2,000 kcal, of which 200 kcal is provided by fat, the fat-energy percentage is 10.

Energy and protein requirements

The total amount of energy and protein needed by different individuals varies a great deal, depending primarily on the amount of physical activity but also on age, sex, body size and, to some extent, climate. Extra energy is needed during pregnancy and lactation.
An average population, made from people of all age and gender, will need 2,100 kcal per day. Energy requirement will vary with age, sex, physical activity, climate, etc.