The National Institutes of Health
From NIH Research Matters (NIH)
July 17, 2012
The mix of carbohydrate, fat and protein in your diet may be a critical factor in maintaining weight loss, a new study reports. The finding suggests that, to the body, not all calories are created equal.
Many people have difficulty keeping weight off once they've lost it. Only 1 in 6 overweight people will maintain at least 10% of their weight loss. Weight regain is often caused by reduced motivation or commitment to diet and exercise. In addition, weight loss slows the body's metabolism, making it more difficult to burn calories.
A research team, led by Drs. Cara Ebbeling and David Ludwig at Boston Children's Hospital, explored the effects of different diets on the ability to burn calories after weight loss. Their 4-year study was funded in part by NIH's National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and National Center for Research Resources (NCRR).
The team recruited 21 adults, ages 18 to 40, and placed them on an initial diet to lose 10% to 15% of their body weight. All participants began the study with a body mass index (a ratio of weight to height) of 27 or higher, classifying them as overweight or obese. After their weight loss, the participants followed 3 different diets in random order, each for 4 weeks at a time.
The diets had the same number of calories, but varied in their levels of carbohydrate, fat and protein. One diet was low-fat, with 60% of calories from carbohydrate, 20% from fat and 20% from protein. The second was a low-glycemic index diet (designed to prevent spikes in blood sugar), with 40% of calories from carbohydrate, 40% from fat and 20% from protein. The third was a very-low carbohydrate ("Atkins") diet, with 10% of daily calories from carbohydrate, 60% from fat and 30% from protein. The study was published on June 27, 2012, in the Journal of the American Medical Association.
The scientists measured the participants' energy expenditure and other aspects of metabolism. They found that the number of calories burned daily differed among the 3 diets. On average, the very-low carbohydrate diet resulted in 3,137 daily calories burned. That was 200 more daily calories burned than the low-glycemic diet (2,937) and 325 more than the low-fat diet (2,812). Hormone levels and other metabolic measures also varied by diet.
Although the very-low carbohydrate diet produced the most improvement in metabolism, the participants had higher levels of known risk factors for diabetes and heart disease, most notably the stress hormone cortisol. The low-glycemic index diet appeared to have benefits similar to the very-low carbohydrate diet with fewer negative effects. The researchers suggest that eating low-glycemic foods like less-processed grains, vegetables and legumes may be the best choice for lasting weight loss and heart disease prevention.
"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," Ebbeling says. "Unlike low-fat and very-low carbohydrate diets, a low-glycemic index diet doesn't eliminate entire classes of food, likely making it easier to follow and more sustainable."
-by Miranda Hanson, Ph.D.