Low-Fat Vs. Low-Carb Diets

April Daniels Hussar,SELF magazine

As much as we tout healthy eating, many women still flock to the latest fad diet. But according to a new study, the best diet is neither low-fat nor low-carb...

The study from Boston Children's Hospital, published today in the Journal of the American Medical Association, compared a low-fat diet, a very low-carb diet and a low-glycemic index diet (a diet that emphasizes complex carbs that are digested slowly), and found that a low-glycemic index diet may be your best bet.

First, participants were fed a standard diet so they'd lose 10-15 percent of their initial body weight. Then, they were fed the three different diets in random order for four weeks each in order to measure how different diets affect metabolism following substantial weight loss.

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"Both the low-glycemic index diet and the very low carbohydrate diet were designed to prevent surges in blood glucose after a meal," Cara Ebbeling, Ph.D., associate director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital and one of the co-authors of the study, tells HealthySELF. "For the low-glycemic diet, this was accomplished by focusing on sources of complex carbohydrates that are digested slowly, like non-starchy veggies, fruits, beans and minimally processed grain products. The low-carb diet accomplished this by restricting carbohydrates."

After each four-week period of each diet, Ebbeling and her colleagues measured the participants' energy expenditure -- i.e., how many calories they burned both at rest and over the course of the day.

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According to Ebbeling, the rate at which your body burns calories decreases with weight loss, which is one reason why keeping weight off can be such a challenge. This study found that the decrease in calorie expenditure was greatest with the low-fat diet, meaning you burn the fewest calories on a low-fat plan.

And, while you burn the most calories on a low-carb diet, Ebbeling says a low-carb diet also puts your body under stress, raising markers that indicate an increased risk for cardiovascular disease.

"The low-glycemic diet may be the happy medium," says Ebbeling, because it helps you burn more calories than a low-fat diet (though not as many as a very low-carb diet), and doesn't cause any of the health risks of an extremely low-carb diet. What it ultimately comes down to, she says, is focusing on quality, not quantity of food.

"There has been a lot of focus on restricting a single nutrient, whether all fat or all carbohydrates," says Ebbeling, "but it's best to take a moderate approach."

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Angela Ginn, registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics, agrees. "All calories are not created equal," she says. According to Ginn, many studies have shown that low-carb diets may help you lose weight faster, but they may not help you maintain that weight loss over time. She says, "This study shows that the quality of your calories really matters."

According to both Ginn and Ebbeling, a fiber-rich, low-glycemic diet encourages healthy food choices such as minimally processed and whole grains, fruits, non-starchy vegetables, milk and healthy fats like avocados and olive oil.

Ebbeling also notes it's important to moderate your sugary treats, and to have them only after a balanced meal. In sum, says Ginn, "A low-glycemic index diet can be more satisfying and a permanent lifestyle change."

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