'Energy density' is the amount of energy (or calories) per gram of food. Lower energy density foods provide fewer calories per gram of food – this means that you can have satisfying portions of these foods with a relatively low calorie content. Evidence suggests that diets with a low energy density can help people maintain a healthy body weight.
Low energy density foods include foods with a high water content, such as soups and stews, foods like pasta and rice that absorb water during cooking, and foods that are naturally high in water, such as fruit and vegetables. Fibre in foods like wholegrains and potatoes with skin can also help to reduce energy density. High energy density foods tend to include foods that are high in fat and have a low water content, for example biscuits and confectionery, crisps, peanuts, butter and cheese.
Studies have shown that people tend to consume about the same amount (weight) of food each day, but not necessarily the same amount of energy (or calories). So it may be possible to consume less energy, without feeling hungrier, by eating a lower energy density diet, which still makes up the same weight of foods overall throughout the course of a day.
This is probably best illustrated with an example – the image below shows two portions of a fruit-based dessert – they are very different in size but actually both contain about the same amount of calories! The difference is that the one on the left has a low energy density, while the one on the right has a high energy density. Basically, by choosing the lower energy density option, you get to eat a lot more food for the same number of calories!
How is energy density calculated?
You can calculate the energy density of foods if you know the weight of a serving of the food (in grams) and the amount of calories that serving contains. The energy density of a food is the number of calories divided by the weight.
Energy density = no of calories/weight (grams)
So using the desserts above as an example, they both contain about 215 kcal, but the one on the left weighs 300 g while the one on the right only weighs 140 g. Therefore:
The energy density of the dessert on the left (mixed berries, low fat plain yogurt and sprinkling of granola) = 215 kcal/300 g = 0.7
The energy density of the dessert on the right (strawberries and cream) = 215 kcal/140 g = 1.5
So although the two desserts have a similar calorie content, the one on the left has a much lower energy density than the one on the right and so the portion is twice as much as the other dessert.
Very low energy density foods = less than 0.6 kcal/g
Low energy density foods = 0.6 to 1.5 kcal/g
Medium energy density foods = 1.5 to 4 kcal/g
High energy density foods = more than 4 kcal/g
It is better to base the diet around foods that are low or very low in energy density, to consume moderate amounts of some medium energy density foods and consume higher energy density foods in small amounts and less often, as demonstrated in the Eatwell Guide.