A commonly used phrase when referring to nutrition is “a calorie is a calorie,” which can be misleading. A calorie is a measurement of energy; it’s the amount of energy needed to raise one gram of water one degree Celsius.
Over time, however, calories have come to be associated with human biology, not just with energy measurement. It is true, from an actual energy standpoint, that in a closed loop system all calories are equal. It’s when we look at what happens to a calorie after it’s ingested, that we start seeing some important differences that depend on the source of the calorie.
Although all foods provide energy to the body, foods also deliver nutrients, influence hunger, and trigger different hormonal pathways.
Consider 100 calories derived from table sugar compared to 100 calories derived from olive oil; these calories have different speeds and pathways of digestion, trigger different hormonal pathways, and can have different impacts on weight management and overall health.
So when considering calories, it makes more sense to not just consider the total amount of energy derived from a calorie, but also daily nutrient needs. Dietitians recommend a focus on the nutrient quality of calories, not just total calorie quantity – an approach referred to as nutrient density.
Nutrient density is an approach that promotes getting as much out of total daily calorie intake as possible, and striving to meet not only energy needs but also vitamin, mineral, and other nutrient and biological needs from those total calories.