There’s a common myth in dieting that it doesn’t matter where your calories come from — as long as you restrict them, you can lose weight. While that is true in the short term, restricting your calories without regard to where they’re coming from can actually inhibit your ability to lose weight and keep it off in the future. Your metabolic system is complex; achieving permanent and healthy weight loss is much more complicated than “calories in, calories out.” In fact, restricting calories on a high-carb diet can actually have very harmful effects on your body.
The kind of calories you consume (fats, proteins, or carbs) has as much impact on your long-term ability to lose weight as the number of calories you eat. In a 1956 article, Alan Kekwick and Gaston Pawan explored diets with equally restricted calories but differing amounts of fat and protein. Diets high in fat, even at the exact same calorie count, resulted in more weight loss than ones high in carbs. We now know that this is because high-fat diets like keto engage the body’s fat burning engine as well as limit the production of insulin, the fat-storage hormone.
Not only will you lose more weight on a high-fat diet, you’ll lose it in a healthier way. Given a choice between breaking down carbs or fat for energy, your body will always pick carbs: they are less energy-dense than fat (4 calories per gram as opposed to the 9 in a gram of fat) and thus easier to break down. High-carb diets, then, never give your body a chance to shift from one fuel source to the other. So when calories are restricted in this case, your body begins to enter starvation mode: slowing metabolism and breaking down organ and muscle tissue for the energy it needs. The added insulin from consuming so many carbs also inhibits the burning of fat and actually promotes fat storage.
High-fat diets, on the other hand, never put your body into starvation mode. On the contrary, being in ketosis means that your body is primed to get all of the extra energy it needs from stored body fat and not by slowing metabolism or breaking down important tissues.
A calorie is not just a calorie — while counting them is an essential part of any diet, what you eat to get them matters a lot!