Two new diet studies that appear to reach opposite conclusions on whether certain diets work better for weight loss have left me scratching my head. Both were published this week in highly respected medical journals, but one found that following a high-fat, Atkins-style diet for 12 months led to more weight loss than a low-fat diet, while the other found that it didn’t matter which diet people followed, they all lost similar amounts of weight over the course of a year simply by cutting calories.
The first finding, published Monday in the Annals of Internal Medicine, randomly assigned nearly 150 people to follow either a low-fat or low-carbohydrate eating plan and found that those in the low-carbohydrate group lost an average of nearly 8 pounds more by the end of the study compared to those who followed a low-fat diet. The low-carbohydrate group — which limited their carbohydrate intake to no more than 30 percent of total calories — also lost more body fat compared to muscle and experienced a greater improvement in their cholesterol levels and overall heart disease risk compared to those who limited their fat intake to no more than 30 percent of calories.
On the other hand, a review of 48 randomized weight loss trials published Tuesday in the Journal of the American Medical Association found that both low-fat and low-carbohydrate diets led to a 16-pound weight loss over a year compared to following no diet. This led the researchers to conclude that weight loss differences between diet plans like the low-carbohydrate Atkins and Zone diets and low-fat Ornish plan “were minimal” and that overweight folks should try any diet that’s easy to stick with in order to lose weight and keep it off.
I asked cardiologist Dr. Dariush Mozaffarian, dean of the Friedman School of Nutrition Science and Policy at Tufts University, to sort out the confusion. Here are edited excerpts from our interview.
How is it possible that two groups of reputable researchers could reach such diametrically opposed findings on these diet studies?
There are two important differences between these studies that show they’re not contradictory. In the single trial published in the Annals journal, researchers didn’t ask people to reduce their calorie intake but just instructed them to change the composition of their diet — eating fewer carbohydrates or less fat. In the JAMA meta-analysis looking at commercial diet plans, participants reduced how much they ate and also altered their diet composition, so it’s impossible to know what actually led to the weight loss.
You have reached the limit of 5 free articles in a month
Stay informed with unlimited access to Boston’s trusted news source.
- High-quality journalism from the region’s largest newsroom
- Convenient access across all of your devices
- Today’s Headlines daily newsletter
- Subscriber-only access to exclusive offers, events, contests, eBooks, and more
- Less than 25¢ a week