Energy balance

Low-carbohydrate diets do not increase energy expenditure (resting metabolic rate, thermic effect of food, or physical activity) compared to low-fat diets, and thus cannot explain the greater weight loss observed in low-carbohydrate dieters.

If you are losing more weight on a low-carb diet than a low-fat diet, it is not because your body is burning more calories. Your resting metabolism and the energy cost of digesting food are similar to those on a low-fat diet. The difference likely comes down to how much you actually eat, which may be harder to track accurately on a restricted low-fat diet.