A Calorie is a Calorie… Or is it?
Well, the answer is Yes… And No.
Yes, a calorie is a calorie, because it is impossible for a human being (or any other creature, machine, or process) to break the laws of thermodynamics. Just can’t happen. A calorie is a unit of measure (like an inch or a gallon). Instead of measuring distance or volume, a calorie measures energy. Calories measure the amount of energy stored in a piece of food as well as the amount of energy used to perform a particular activity.
Every day, our bodies require a certain amount of energy (aka a certain number of calories) to maintain basic functions (like digestion, heart rate and breathing) and allow us to perform our chosen activities. These calories might come from our food, or they might come from stored body fat or other tissues. If we eat more calories than our body uses on a given day, we MUST store the rest (usually as fat). If we eat fewer calories than our body needs, then our body MUST get the remaining calories from somewhere (usually by breaking down body fat).
No, a calorie is not simply a calorie, because calories from different sources have different effects on the body. Carbs, proteins and fats are all digested and utilized differently in the body. Different foods also contain different amounts of vitamins, minerals, antioxidants, fibre, and other nutrients. They have different effects on our hormone levels; and therefore our moods, energy and hunger levels.
Example #1: A bag of potato chips is essentially devoid of all nutrition. It contains a bunch of calories (from carbs and fat), and probably a bunch of toxic chemicals as well (think of all the additives). A baked yam also contains a bunch of calories (mostly carbs), but it is loaded with vitamins, minerals and other nutrients that your body needs.
Example #2: Eating carbs causes the body to release the hormone insulin. Insulin allows carbs into the muscle cells where the energy is used to fuel cellular activities, and into the fat cells where the energy is stored as fat. But insulin also prevents fat from getting out of the fat cells. In the case of chronically high insulin levels, the body has the ability to store energy as fat, but can’t use stored fat for energy. Once the body runs out of carbohydrates, it gets hungry (instead of switching fuel sources and burning stored energy, aka body fat, instead). Gary Taubes has written two excellent books on this topic: Good Calories, Bad Calories and Why We Get Fat. A fantastic review and summary of Why We Get Fat can be found here.
Clearly, WHAT we eat is equally important as HOW MUCH we eat.