The carbohydrate-insulin model argues that overeating isn’t the underlying cause of long-term weight gain. Instead, it’s the biological process of gaining weight that causes us to overeat.
Here’s how this hypothesis goes: Consuming processed carbohydrates (especially refined grains, potato products and sugars), causes our bodies to produce more insulin. Too much insulin, one of the most powerful hormones, forces our fat cells into calorie-storage overdrive. These rapidly growing fat cells then hoard too many calories, leaving too few for the rest of the body. So we get hungry, and if we persist in eating less, our metabolism slows down.
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Scientists have known for decades that diet composition, apart from calories, can affect hormones, metabolism and even the very workings of our genes. And a lot of research supports the carbohydrate-insulin model. But it hasn’t been rigorously tested before because high-quality clinical nutrition trials that control exactly what everyone eats for months are expensive — so they rarely get done.
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Participants in the low (20%) carbohydrate group burned on average about 250 calories a day more than those in the high (60%) carbohydrate group, just as predicted by the carbohydrate-insulin model. Without intervention (that is, if we hadn’t adjusted the amount of food to prevent weight change), that difference would produce substantial weight loss — about 20 pounds after a few years. If a low-carbohydrate diet also curbs hunger and food intake (as other studies suggest it can), the effect could be even greater.