The conventional wisdom, and the mainstream approach to diet and exercise is that you must balance "calories in" with "calories out." What does that really mean? I'm going to attempt to answer that from my perspective, and talk about why I think it is more or less true, yet misguided advice. While calories in may balance calories out, a low carbohydrate approach can take the natural processes that our bodies use and turn them to our advantage. We can make the process of improving our body composition and improving overall health (usually that also means losing weight) relatively easy and automatic, instead of a tremendous feat of willpower.
The conventional wisdom on diet and exercise can be summed up in the concept that the calories in the food you eat (calories in) is either burned up, or is converted to fat. When you exercise you burn calories (calories out.) Part of the “calories out” is your “basal metabolic rate” which is simply the energy your body needs to stay alive, even if you are doing nothing else. The idea is that this simple equation governs whether we gain or lose weight. If we eat more and don't exercise more, we gain weight. If we eat less or exercise more, we lose weight. When put this simply, it’s essentially true, but there are more things going on and our bodies aren't that simple, and how easy it is to hold that equation in balance can depend a lot on what kind of calories you consume.
If we eat a conventional diet, high in carbohydrates and low in fat, we really can affect our body composition by consciously limiting our intake of calories and constantly exercising to burn calories (think “The Biggest Loser”). If you can do that, you can improve body composition, lose weight, and be fit. The problem is, you will have to really work at it, you’ll need to have strong willpower. (Think “The Biggest Loser” again and all the made-for-TV drama as the contestants struggle to stay on the program, driving themselves or being driven to exhaustion, while basically starving.)
If we try to limit our food intake, we are fighting our own body’s chemistry and will have a real struggle. The primary reason this happens, is that when we consume carbohydrates, they quickly turn to glucose in the blood. (See my post on why LCHF diets work.) As glucose goes up after a meal, it must be removed from the bloodstream since too much is toxic so insulin is secreted. Insulin drives blood glucose back down. Assuming someone on the standard American diet high in carbohydrates, the constant insulin surges keep the body form having access to burning fat so when blood glucose drops, this signals more hunger which must be countered with sheer willpower.
If we try to hold our “calories in” the same and just try to burn more calories (exercise more) we run into another problem. Our bodies know we’ve burned a lot of calories. If we are consuming a high carbohydrate diet, we can’t access our stored body fat because the constant insulin surges cause fat cells to hold on to their fat stores. This leads to fuel not being available, particularly to the brain which triggers an overwhelming drive to find food. Unless we have tremendous willpower, we’re going to eat more and cancel out all that work we did to burn more calories.
The worst case of ramping up exercise and forcing ourselves eat less compounds the problem. And if we're constantly exercising (again, like you see on "The Biggest Loser") you crank up cortisol (the "fight or flight" response) which also triggers the body to hold on stored fat and more hunger.
If we eat a low carbohydrate diet, we still have to eat fewer calories than we burn, more or less, if we want to lose weight. The advantage with this approach is that without the constant insulin surges, our fat cells are more than happy to provide the energy the body needs, and we don’t experience the drive the eat. In fact, if we have some fat to lose, our bodies will actually seek ways to burn more of our fat, giving us a tremendous amount of energy.
So we’re not violating some natural law that calories in equal calories out. We’re not cheating the system. We’re leveraging the body’s natural systems to our advantage. Turning from the need for a an almost superhuman feat of willpower, to an almost effortless, automatic, and quite natural process.