High-calorie foods, and why to read this ranking backwards

Energy is how much the body can extract from a food. The conversion is 4 kcal per gram of carbohydrate, 4 per gram of protein, 9 per gram of fat and 7 per gram of alcohol. These are the Atwater factors, averages that have been in use for over a century. The body spends that energy holding its temperature, beating its heart and moving its muscles. Most of the total goes on simply existing; what exercise adds is smaller than people expect.

The figure used on food labels is 2,000 kcal a day. That is a labelling convention, not a personal target. Real requirements run from around 1,600 kcal to well over 3,000 depending on body size, age, sex and activity. Either way, the ranking below is not a list of foods to eat less of. A tablespoon of oil is 14 g and 124 kcal, which is about what a day's cooking uses; a handful of nuts is 170 to 200 kcal and brings satiety and nutrient density with it.

Atwater factors are averages, and for some foods they are wrong. Nuts are the best-documented case: studies measuring almonds and pistachios report that the energy actually absorbed runs around 20% below the label, because fat stays trapped inside plant cell walls and passes through. The reverse also happens — finely ground or long-cooked foods are absorbed at or above the labelled figure. Fibre is another mismatch: indigestible fibre yields almost no energy but still sits inside the carbohydrate column.

Do not read this ranking as a list of foods to avoid. The top of it is oils and nuts, both of which this site recommends. High energy density means a lot of energy in a small volume; it does not mean harmful. And weight is not a question of calories alone — at the same energy, foods high in protein and fibre keep you full longer, while highly processed foods make the same calories easier to eat quickly. Cutting energy too far is its own problem: held below requirement for long, it affects muscle, bone density and hormones. If you have a weight goal, do not look only at a daily total — talk to a clinician or a dietitian.