Low-fat vs. low-carb dieting: the latest in the diet wars

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Screen Shot 2014-04-21 at 1.30.14 PMEver since the late Dr. Atkins published his very-low carbohydrate diet in the early 1970s, there has been dissention among nutritional experts on the utility and safety of this diet species. In particular, its efficacy for weight loss as well as its effect on the risk of heart disease has been questioned, compared to reduced fat diets that are currently recommended by, for example, the American Heart Association. And various studies have found conflicting results some indicate that low fat diets can promote more weight loss, while others have found the opposite.

The latest report, just published in the Annals of Internal Medicine, comes down on the side of the low-carb version for both weight loss and for decreasing cardiovascular risk factors. Led by Dr. Lydia A. Bazzano of Tulane University School of Public Health and Tropical Medicine in New Orleans, the researchers studied 148 persons, most of whom were women in their late 40s. Forty-five percent were white, and about 38 percent were black. All were obese, with average BMIs of 36 to 37 m/kgm2.

Seventy-three participants were randomly assigned to follow a low-fat diet, which was to be less than 30 percent of calories from fat, and the rest were assigned to the low-carbohydrate group; the members of this group ate a diet with no more than 40 gm/day of digestible carbohydrates (sugars and starches). Participants were instructed on their respective diets by dietitians, who met with them weekly for the first month, decreasing to monthly for the last 6 months of the study. Researchers collected food intake data at the beginning of the study, and at 3, 6, and 12 months. None of the participants was given a calorie limit to observe.

Key results of the study included a significantly greater weight loss in the low-carb diet group at every time point. By the final, one year time point, the low-carb group had lost a greater amount of body fat, and less lean body mass than the low-fat group. In addition, the low-carb group significantly increased their levels of HDL (good) cholesterol, compared to the low-fat group, and significantly decreased their levels of blood triglycerides.

The authors acknowledged that a weakness of their study was the lack of a cardiovascular disease endpoint (e.g., did the low-carb group have fewer heart attacks than the low-fat group). In their discussion they concluded that a low-carbohydrate diet induced greater weight loss and reductions in cardiovascular risk factors at 12 months than a low-fat diet.

ACSH friend, Dr. David Seres, Associate Professor of Medicine in the Institute of Human Nutrition, and Director of Medical Nutrition, Columbia University Medical Center, commented, It is interesting that this small study has garnered so much attention in the press. While the pendulum is swinging back toward favoring high fat diets for weight loss, nutrition research usually marches on at a snail s pace, not in huge discoveries. This study is one of the first to look at these issues in the way they did, and kudos to them if indeed they were able to create durable dietary change for as long as was done. That s hard to do. But there are as many studies saying that low fat diets work at least as well as low carb diets. You would think there would be some consensus after all the research that has been done on these dietary approaches since they were first promoted by William Banting (an undertaker) and the eponymous James Salisbury (of Salisbury steak fame) in the late 1800s.