Energy and Thermal Physics

Energy density of foods

Stories from Physics for 11-14 14-16 IOP RESOURCES

Rather than simply comparing the absolute calorific value of foods, energy density can be a useful measure. Feeling hungry is one of the challenges of dieting, so foods which provide relatively few calories per unit mass – i.e. they have a low energy density - may provide a feeling of fullness with limited calorie consumption.

  •  Low energy density foods are defined as those which contain less than 2.5 kJ/g or 0.6 kcal/g. They include non-starchy fruits and vegetables
  •  High energy density foods contain 17-38 kJ/g or 4-9 kcal/g and include biscuits, crisps and peanut butter.
  •  In general, fats have a higher energy density, at around 38 kJ/g or 9 kcal/g, than protein or carbohydrate, both around 17 kJ/g or 4 kcal/g.
  •  The World Cancer Research Fund has recommended that the mean energy density of a person’s diet should be 5.23 kJ/g or 1.25 kcal/g. The diets of subsistence farmers in Gambia averaged 4.50 kJ/g or 1.08 kcal/g, excluding drinks. This compared to 6.70 kJ/g or 1.6 kcal/g for Western diets. A study of Scottish diets reported that individuals in the most deprived areas ate diets with higher energy densities than those in the least deprived areas.


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