First, this was a short trial in people who’d lost a lot of weight very quickly.
This kind of weight loss usually induces a sharp drop in daily calorie-burning – both at rest and while you’ve modestly active – which makes it harder to maintain the loss.
In fact, only one in six overweight people maintain even 10 percent of their weight loss over the long term.
So this study was designed to see what proportions of carbs, fat, and protein did the best job of preventing a drop in the amounts of calories burned in the course of a day.
Second, many media headlines got this one wrong, in that they called it a study on “weight loss” when it was only about maintaining weight loss.
Let’s take a closer look
Boston study supports Atkins-style diet, low in carbs
The trial was conducted by the New Balance Foundation Obesity Prevention Center Boston Children’s Hospital (Ebbeling CB et al. 2012).
In short, the results showed that diets proven to reduce the surge in blood sugar after a meal – either a low-glycemic index (GI) diet or a very-low carbohydrate diet – may be preferable to a low-fat diet for maintaining weight loss.
(Low-GI carbohydrates digest slowly, helping to keep blood sugar and hormones stable after the meal.)
Although the very low-carb diet came out on top, the low-GI diet had similar metabolic benefits, without the stress and inflammation experienced by participants consuming the very low-carb diet.
Weight regain is often attributed to a decline in motivation or adherence to diet and exercise, but biology also plays an important role.
After weight loss, the rate at which people burn calories (known as energy expenditure) drops, reflecting slower metabolism.
Lower energy expenditure adds to the difficulty of weight maintenance and helps explain why people tend to re-gain lost weight.
Prior research by the same team showed the advantages of a low-GI diet for weight loss and diabetes prevention ... but the effects of these diets during weight loss maintenance has not been well studied.
The 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,” said Foundation director David Ludwig, M.D.
“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.” (BCH 2012)
Each of the study’s 21 adult participants (ages 18 to 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 rigorous observation of how each diet affected all participants, regardless of the order in which they were consumed:
The low-fat diet – which emphasized whole grain products and a variety of fruits and vegetables – provided 60 percent of daily calories from carbohydrates, 20 percent from fat, and 20 percent from protein.
The low-GI diet emphasized minimally processed grains, vegetables, healthy fats, legumes, and fruits, with 40 percent of its daily calories coming from carbohydrates, 40 percent from fat, and 20 percent from protein.
The low-carbohydrate diet – which was modeled after the Atkins diet – provided 10 percent of daily calories from carbohydrates, 60 percent from fat and 30 percent from protein.
The study used state-of-the-art methods such as stable isotopes to measure 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-carb (high-fat) diet produced the smallest drop in calorie-burning: 100 calories less per day, vs. 300 and 400 less per day among people on the very-low-fat (high-carb) and low-GI diets, respectively.
Better yet, eight of the 21 subjects on the Atkins-style diet expended more calories per day than they did at their full weights … the opposite of the predicted metabolic response.
Though a low-fat diet is recommended by the U.S. government and the American Heart Association, it caused the greatest drop in energy expenditure, an unhealthy blood-fat profile, 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 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.” (BCH 2012)
The study was funded by The National Institute of Diabetes and Digestive Kidney Diseases, the National Center for Research and Resources, the National Institutes of Health, and the New Balance Foundation.
Boston Children’s Hospital (BCH). Study challenges the notion that a calorie is just a calorie. June 26, 2012. Accessed at http://childrenshospital.org/newsroom/Site1339/mainpageS1339P891.html
Ebbeling CB, Swain JF, Feldman HA, Wong WW, Hachey DL, Garcia-Lago E, Ludwig DS. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA. 2012 Jun 27;307(24):2627-34. Accessed at http://jama.jamanetwork.com/article.aspx?articleid=1199154