Q. What do nutritionists mean when they talk about “energy density”?

A. Energy density means the ratio of kilojoules/Calories you get from a given weight or volume of a food. It's really how many kilojoules or Calories you can fit into a mouthful! It's usually given in kilojoules per 100 grams or 100 mLs.

For instance fruit is mainly low in energy density while chocolate is high:

fruit                       230 kJ per 100g               = low energy density

chocolate         2160 kJ per 100g                  = high energy density

Most modern-day snacks are energy-dense, a factor contributing to the present obesity crisis.  They pack a lot of energy (kilojoules or Calories) into a small volume. Compare at these kilojoule counts per 100 grams:

In contrast, most (but not all) basic foods have a low energy density:

Foods that have a low energy density have lots of water or fibre, while energy dense foods have little water (which concentrates the nutrients as in chocolate or crisps) or high in fat.

Water and fibre both contribute bulk and volume without adding kilojoules as in soup or salads – which is why they feature in weight loss diets so often. The more water and fibre present, the less room for fat or carbohydrate or sugar.