NEJM: Low-fat diets not best for weight loss: New study by Ben-Gurion U. of the Negev

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In the two-year study, 322 moderately obese people were intensively monitored and were randomly assigned one of three diets: a low-fat, calorie-restricted diet; a Mediterranean calorie-restricted diet with the highest level of dietary fiber and monounsaturated/saturated fat; or a low-carbohydrate diet with the least amount of carbohydrates, highest fat, protein, and dietary cholesterol. The low-carb dieters had no caloric intake restrictions.

Although participants actually decreased their total daily calories consumed by a similar amount, net weight loss from the low-fat diet after two years was only 6.5 lbs. (2.9 kg) compared to 10 lbs. (4.4 kg) on the Mediterranean diet, and 10.3 lbs. (4.7 kg) on the low-carbohydrate diet. "These weight reduction rates are comparable to results from physician-prescribed weight loss medications," explains Dr. Iris Shai, the lead researcher.

The low-fat diet reduced the total cholesterol to HDL ratio by only 12 percent, while the low-carbohydrate diet improved the same ratio by 20 percent. Lipids improved the most in the low-carbohydrate, with a 20% increase in the HDL ("good") cholesterol and, 14% decrease in triglycerides. In all three diets, inflammatory and liver function biomarkers was equally improved. However, among diabetic participants, the standard low-fat diet actually increased the fasting glucose levels by 12mg/dL, while the Mediterranean diet induced a decrease in fasting glucose levels by 33mg/dL.

In addition to the findings, this two-year study is also significant because of the relatively large number of participants coupled with a low drop-out rate - 95 percent were in the study after one year and 85 percent were still participating after the second.

Dr. Iris Shai is a researcher at the S. Daniel Abraham International Center for Health and Nutrition in the Department of Epidemiology at Ben-Gurion University of the Negev. She conceived the study with Dr. Stampfer, the senior author, while she was a Fulbright fellow at Harvard School of Public Health and Channing Laboratory in Boston, Massachusetts.

The trial conducted at the Nuclear Research Center in Israel involved unparalleled and significant cooperation between staff, participants and their spouses. The cafeterias in the workplace went through a "health revolution," integrating the workplace cafeteria managers with clinical support and a nutritional advisor, in order to provide healthy food dishes that would fit each one of the dietary arms, as labeled with specific colors every day. Along with careful workplace nutritional counseling, spouses of the trial participants were educated on how to keep the specific assigned diet strategy at home. The participants also completed electronic questionnaires, developed specifically for the study.

"The Nuclear Research Center Dimona highly values health promotion within the workplace," said Dr. Dan Schwarzfuchs, director of the clinical department at the facility. "This is why it supported performance of such a nutritional study and enabled the outstanding adherence rate of the DIRECT participants."

"Clearly, there is not one diet that is ideal for everyone," Shai concludes. "We believe that this study will open clinical medicine to considering low-carb and Mediterranean diets as safe effective alternatives for patients, based on personal preference and the medical goals set for such intervention. Furthermore, the improvement in levels of some biomarkers continued until the 24-month point, although maximum weight loss was achieved by 6 months. This suggests that healthy diet has beneficial effects beyond weight loss."

American Associates, Ben-Gurion University of the Negev