Weight regain is often attributed to a decline in motivation or adherence to diet and exercise, but biology is also a factor. After weight loss, the rate at which people burn calories decreases, reflecting slower metabolism. Lower energy expenditure adds to the difficulty of weight maintenance and helps explain why people tend to regain lost weight.
Prior research by Cara Ebbeling, PhD, associate director and David Ludwig, MD, director of the New Balance Foundation Obesity Prevention Center Boston Children's Hospital, found advantages to a low glycemic load diet for weight loss and diabetes prevention, but the effects of these diets during weight loss maintenance have not been well studied. Statistics show that only one in six overweight people will maintain even 10 percent of their weight loss long-term.
The current study suggests that a low-glycemic load diet is more effective than conventional approaches at burning calories and keeping energy expenditure at a higher rate after weight loss. "We've found that, contrary to nutritional dogma, all calories are not created equal," says Ludwig. "Total calories burned plummeted by 300 calories on the low fat diet compared to the low carbohydrate diet, which would equal the number of calories typically burned in an hour of moderate-intensity physical activity."
Each of the study's 21 adult participants, ages 18-40, first had to lose 10 to 15 percent of their body weight, and after weight stabilization, completed all three of the following diets in random order, each for four weeks at a time. The randomized crossover design allowed for observation of how each diet affected all participants, regardless of the order in which they were consumed:
- A low-fat diet, which reduces dietary fat and emphasizes whole grain products and a variety of fruits and vegetables, comprised of 60 percent of daily calories from carbohydrates, 20 percent from fat and 20 percent from protein.
- A low-glycemic index diet made up of minimally processed grains, vegetables, healthy fats, legumes and fruits, with 40 percent of daily calories from carbohydrates, 40 percent from fat and 20 percent from protein. Low glycemic index carbohydrates digest slowly, helping to keep blood sugar and hormones stable after the meal.
- A low-carbohydrate diet, modeled after the Atkins diet, comprised of 10 percent of daily calories from carbohydrates, 60 percent from fat and 30 percent from protein.
The study measured participants' total energy expenditure, as they followed each diet. Each of the three diets fell within the normal healthy range of 10 to 35 percent of daily calories from protein. The very low-carbohydrate diet produced the greatest improvements in metabolism, but with an important caveat: This diet increased participants' cortisol levels, which can lead to insulin resistance and cardiovascular disease. The very low carbohydrate diet also raised C-reactive protein levels, which may also increase risk of cardiovascular disease.
Though a low-fat diet is traditionally recommended by the U.S. Government and Heart Association, it caused the greatest decrease in energy expenditure, an unhealthy lipid pattern and insulin resistance.
"In addition to the benefits noted in this study, we believe that low-glycemic-index diets are easier to stick to on a day-to-day basis, compared to low-carb and low-fat diets, which many people find limiting," says Ebbeling. "Unlike low-fat and low-very-carbohydrate diets, a low-glycemic-index diet doesn't eliminate entire classes of food, likely making it easier to follow and more sustainable."
Published in the Journal of American Medical Association