Low-carb diets better job of keeping metabolism

Low-carb diets do a better job of keeping metabolism on track when people are trying to lose weight, and that might be helping people keep the pounds off for good, shows a new study.

The authors explain carbohydrates such as white bread, refined breakfast cereals, and white sugar are rapidly digested, thus causing a quick rise in blood sugar and insulin.

This leads the body to slow the metabolism, causing people to feel hungrier sooner.

Low-carb diets, however, emphasize foods that are digested more slowly, such as whole grains, fruits and nuts. Blood sugar rises more slowly, and metabolism remains more normal.

“The idea that ‘a calorie is a calorie is a calorie’ doesn’t really explain why conventional weight-loss diets usually don’t work for more than a few months,” says study author Dr. David Ludwig, from Children’s Hospital Boston.

“Almost anyone can lose weight in the short-term -- very few keep it off in the long-term. That’s given rise to the notion that the body has a ‘setpoint’ and that when you diet, internal mechanisms work to restore your weight to that setpoint.”

Low-carb diets, he continues, may work better with these internal biological responses to create the greatest likelihood of long-term weight loss.

In this study, Dr. Ludwig and his colleagues compared adults who went on a low- fat diet with those who went on a low-carb diet. Both groups consumed about 1,500 calories a day, and both lost about 10 percent of their body weight.

However, those on the low-fat diet had larger decreases in resting energy expenditures, meaning their metabolisms slowed down significantly more than those on the low-carb diet. Low-carb dieters also reported being less hungry while dieting than those on the low-fat diet.

“Our data suggest that the type of calories consumed -- independent of the amount -- can alter metabolic rate,” says Dr. Ludwig. Now, he plans to conduct a longer study to see if low-carb diets really are better at keeping the weight off.

SOURCE: The Journal of the American Medical Association, 2004;292:2482-2490