Whether to cut carbohydrates or fat to reduce body fat has been a back and forth debate among nutritionists, physical trainers, scientists and doctors. Carbohydrates are on the hit list because they’ve been linked to endocrine adaptations that promote body fat loss more so than reducing fat intake. But a new study published in Cell Metabolism found fat reduction, not carbohydrate reduction, may be more effective at lowering body fat.
After a five-day baseline diet, researchers selectively restricted carbohydrate versus fat for six days in 19 obese adults who were confined to a metabolic ward where they exercised daily (Aug. 13, 2015). Subjects received both isocaloric diets in random order during each of two inpatient stays. Body fat loss was calculated as the difference between daily fat intake and net fat oxidation measured while residing in a metabolic chamber.
Whereas carbohydrate restriction led to sustained increases in fat oxidation and loss of 53 g/d of body fat, fat oxidation was unchanged by fat restriction, leading to 89 g/d of fat loss, and was significantly greater than carbohydrate restriction. Mathematical model simulations agreed with these data, but predicted that the body acts to minimize body fat differences with prolonged isocaloric diets varying in carbohydrate and fat.