A (VERY) BRIEF HISTORY OF CALORIES

The calorie has been used as a dieting tool since the 1910s. Put simply, it’s a unit of energy, originally defined as the amount required to raise the temperature of 1g of water by 1°C. This is how the caloric value of food was measured: you’d burn it in a container surrounded by water, then note the temperature change. These days, a food’s calorie content is calculated by what’s called the Atwater system, or the 4-9-4. This dictates that proteins and carbs contain four calories per gram, while 1g of fat has nine calories. Work out a food’s macro balance and you can calculate its calories. Only recently has this formula started to be called into question. Critics say that not all energy in foods is completely digested or absorbed, and that the Atwater system is flawed because it doesn’t account for how absorption varies according to the type of food or the individual who eats it.

This means it’s hard for people to accurately translate the number of calories on the label to a clear understanding of how much energy these calories will provide.