Think carbs are a dieter's enemy? It turns out restricting one's fat intake leads to a 68% greater loss of body fat than restricting the same amount of calories through carbohydrates in obese adults on strictly controlled diets—and this is in spite of the fact that a low-carb diet reduces insulin and increases fat burning. So says a physicist turned metabolism researcher at the National Institute of Diabetes and Digestive and Kidney Diseases who wanted to test a mathematical model he devised that projected similar results. Reporting in the journal Cell Metabolism, Kevin Hall says that while many believe that cutting carbs reduces fat faster, none had actually tested the impact of cutting carbs while keeping fat at a base line or vice versa. So he checked 19 consenting non-diabetic adults with obesity into to a metabolic ward for two 2-week periods, controlling and accounting for every single bite they ate.
As his model predicted, people lost more body fat when their dietary fat was restricted than when carbs were, even though a low-carb diet does indeed burn more fat. But his model also predicted that in the long term, these differences would become less pronounced for diets that have the same number of calories, according to the press release. "Over the long term, it's pretty close," Hall says. He used data from dozens of controlled feeding studies from decades of nutrition research to develop the model, but he cautions that the study is both small and highly controlled, meaning people's unrestricted diets may cause them to eat differently. "The real world is more complicated than a research lab, and if you have obesity and want to lose weight, it may be more important to consider which type of diet you’ll be most likely to stick to over time," he tells the National Institutes of Health. (See how carbs mess with our metabolism.)