What Is Energy Density? Calories per Gram Explained

Two foods can have the same calories and look nothing alike on a plate. A cup of cooked greens and a spoonful of oil might each carry a similar number of calories, but one fills a bowl and the other barely covers a spoon. Energy density is the figure that captures this difference: calories divided by weight, written as kilocalories per gram.

It is calculated from numbers already on every food page. USDA lists calories per 100 grams, so dividing by 100 gives calories per gram. Nothing about it is estimated.

The bands we use

To make the figure easy to read, our food pages group it into four bands taken from the CDC. The bands come from the CDC's 2008 Research to Practice report on low-energy-dense foods and weight management:

Roughly, water-rich foods such as many vegetables and fruits sit in the lower bands, while foods with little water or a lot of fat sit in the higher ones. The reason is the arithmetic of macronutrients: water has no calories, and fat carries the most energy per gram.

Worked example

Take three foods from our database, with calories per 100 grams from USDA. Dividing by 100 gives the density, and dividing 100 calories by that density gives the weight of food that holds 100 calories:

The spread is the point. One hundred calories is a very large weight of cucumber and a small handful of almonds. Neither is better or worse as a food; the table says only how much space the calories take up.

What you can do with it

Energy density is most useful as a way of reading a plan. When you are working from a calorie deficit, a target is a fixed number of calories, and foods with a lower density let that number cover more weight of food. Higher-density foods do the opposite. Our low-calorie vegetables list and low-calorie fruits list rank foods from the lowest density upward.

The same logic works in reverse for anyone who wants to eat more calories without eating more volume, which is where dense foods fit.

What energy density does not tell you

It describes calories and weight, and nothing else. It says nothing about protein, fiber, vitamins or how a food is made, so a food in either band can be rich or poor in everything else. It also depends on how a food is prepared: cooking in water or oil changes the weight and therefore the density, so the cooked and raw versions of a food can sit in different bands.

Treat the band as a lens, not a ranking of good and bad foods. This is general information, and a doctor or registered dietitian can say what fits your own situation. The CDC source is listed on our sources page, and the method is on how we calculate.