Diet Comparison Challenges Conventional Wisdom on Calories


Does a small study comparing three different diets disprove the long-held belief that all calories are the same for losing weight? Does the same study also prove that carbs are the root of the obesity crisis and an Atkins-style diet is the cure? Those are among the claims putting the study, published in the Journal of the American Medical Association, on the op-ed pages of the New York Times.

David Ludwig, MD, of Boston Childrens Hospital, and colleagues put 21 overweight and obese adults, ages 18 to 40, on a strict 12-week regimen designed to lose 12.5% of their body weight, about 30 pounds. Participants then tried each of three maintenance diets for three weeks:

  • Low-fat, emphasizing whole grains, fruits and vegetables, with 60% of calories from carbohydrates and 20% each from fat and protein.
  • Low-glycemic, similar to the Mediterranean diet, with 40% of calories each from carbohydrates and fat, 20% from protein.
  • Low-carb, similar to the Atkins plan, with 10% of calories from carbohydrates, 60% from fat, 30% from protein.

Researchers measured energy expenditure-calories burned-which dropped across the board after the initial weight loss but varied significantly between the three diets: People burned about 300 calories more per day on the low-carb diet than the low-fat regimen, the equivalent of about an hours moderate physical activity. The low-glycemic diet was in-between, about 150 calories more per day than the low-fat diet.

Times columnist Mark Bittman seized on the findings as proof that low-glycemic diets are the way forward. Although the low-carb, Atkins-like diet scored even better, Bittman noted, it also raised levels of C-reactive protein (CRP), a marker of inflammation, and cortisol, a stress hormone-both linked to long-term heart risk and mortality.

Also writing in the Times, Gary Taubes, author of Why We Get Fat, touted the study as debunking the nutritional truism that a calorie is a calorie. He added, The trial suggests that among the bad decisions we can make to maintain our weight is exactly what the government and medical organizations like the American Heart Association have been telling us to do.

Susan Roberts, PhD, director of Tufts HNRCA Energy Metabolism Laboratory, suggests that everybody take a breath. I think the main thing is this is interesting and no need to doubt the result, but really it needs confirming because 21 participants is a small number, she says.

Dr. Ludwig, she notes, actually sides with Bittman in recommending the middle, low-glycemic diet-a view she echoes. The Atkins-style diet gave a good result on this piece of the puzzle, but that doesnt mean it is the healthiest, for other reasons.

The bottom line, according to Dr. Ludwig, isnt to abandon carbohydrates entirely. Rather, he advises, Its time to reacquaint ourselves with minimally processed carbs-substituting fruit, beans and nuts, for example, for refined carbs. These relatively modest changes can provide great benefit.

TO LEARN MORE: JAMA, June 27, 2012; abstract at


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