One of the reasons why losing weight proves to be so difficult—and why we often end up regaining whatever we’ve lost—is that the basic paradigm behind most diet approaches is wrong. Conventional wisdom around dieting is based on the idea that “calories in should equal calories out.” According to this simple equation, to lose weight you either have to eat less or burn more calories (or both). The underlying assumption is that these two variables are independent of each other.
The reality is more complicated than that. It has been well documented that when we take in too many calories, our metabolism adjusts and starts burning more calories to compensate. The reverse happens when we restrict our calorie intake: our metabolism lowers the amount of calories it burns. Conversely, when we increase “calories out” through exercise, our metabolism adjusts by increasing our appetite. This is why dieting is so hard.