A study published in the BMJ suggests that strictly limiting carbohydrates and eating more fat may help the body burn more calories. The researchers recruited 234 overweight and obese adults for a “run-in” phase, with the goal of losing about 12% of their weight over 10 weeks. Their diets were low-calorie and had moderate amounts of carbs.
Of that group, 164 lost enough weight and moved on to the next phase. They were randomly assigned to either a low-carb, moderate-carb, or high-carb diet for 20 weeks. People on the low-carb diet got 20% of their calories from carbs like vegetables, fruits, and beans; a full 60% of their calories came from fat, including sources like meat, whole milk, cheese, and nuts. The remaining 20% of calories came from protein. The situation was flipped for people on the high-carb plan: 60% of calories from carbs and 20% from fat. The moderate plan divided the two nutrients equally, at 40/40.
After 20 weeks, the low-carb group appeared to be burning more calories—an average of 250 more per day, versus the high-carb group, and 111 more than the moderate-carb group. The researchers did not look at the effects on any further weight loss. Instead, each person’s calorie intake was calibrated to maintain what they’d already lost. The point, explained the researchers, was to zero in on the effects of the different diets on calorie burning.
According to the researchers, the findings support a theory called the “carbohydrate-insulin model.” The premise is that diets heavy in processed carbs send insulin levels soaring, which drives the body to use fewer calories, and instead store more of them as fat.
“Our study suggests that you’ll do better if you focus on reducing refined carbohydrates, rather than focusing on reducing calories alone,” said David Ludwig, co-director, New Balance Foundation Obesity Prevention Center, Boston Children’s Hospital.