Why Not All Calories Are Equal

We’re so often told to eat less and move more to lose weight. The truth is, that this isn’t exactly false but it is very much oversimplified. Essentially, this sentence means eat less calories and burn more calories. However, not all calories are equal. Let us explain.

Before we get into the crux of this, let’s go back to basics and explain what one calorie is. A calorie is the unit of energy required to heat one litre of water by one degree at sea level. In theory, as calories are a unit of energy it would make sense to assume that the less you eat and the more you burn the more weight you’d lose. However, there are a few key components which can explain why not all calories are equal.

Firstly, the number of calories on the back of food packs these days vary significantly and whilst they are generally the best measure that we have at the moment they’re not guaranteed to be 100% accurate.

Secondly, not all foods have the same caloric availability. Caloric availability is the amount of calories which can be absorbed from foods. Some foods such as protein and fibre have a lower caloric availability than others such as sugars and fats.

For example the caloric availability of simple carbohydrates e.g. sugar is around 95%, this means that if you’re consuming 100 calories of simple carbohydrates around 95 of those calories will be absorbed in the body, complex carbohydrates e.g. wholegrains have a 90% caloric availability, fats have a 98% caloric availability and protein has the lowest caloric availability of around 70%. As proteins are made up of amino acids, they need to be broken down into their individual amino acids and this process requires additional calories. As the metabolism of protein is also a timely process it’s more likely to keep you fuller for longer. As a result, if you consume 100kcals of sweets vs 100kcals from an egg, you’re likely to feel fuller from the egg and therefore eat less later on in the day.

Due to the variety in the caloric availability of foods you may be better off focussing on food quality, ensuring that you’re consuming adequate amounts of fibre, micronutrients, vegetables and plant foods in your diet rather than solely focusing on calories. If you are trying to lose weight then aim for a diet which is rich in protein as this is likely to keep you fuller for longer.