Should you skip carbs or fats when dieting?

• Position: YOUR LIFE

Restricting dietary fat leads to body fat loss at a rate 68% higher than cutting the same number of carbohydrate calories when adults with obesity eat strictly controlled diets, according to research conducted at the National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Md.

Carb restriction lowered production of the fat-regulating hormone insulin and increased fat burning as expected, whereas fat restriction had no observed changes in insulin production or fat burning.

"Compared to the reduced-fat diet, the reduced-carb diet was particularly effective at lowering insulin secretion and increasing fat burning, resulting in significant body fat loss," says Kevin Hall, senior investigator and lead study author, "but interestingly, study participants lost even more body fat during the fat-restricted diet, as it resulted in a greater imbalance between the fat eaten and fat burned.

'These findings counter the theory that body fat loss necessarily requires decreasing insulin, thereby increasing the release of stored fat from fat tissue and increasing the amount of fat burned by the body."

The researchers previously had simulated the study with a math model of human metabolism; these body fat predictions matched the data later collected in the study. When simulating what might happen over longer periods, the model predicted relatively small differences in body fat loss with widely varying ratios of carbs to...