A new large scale 2 year study by an international team of scientists concluded that Mediterranean and low carbohydrate diets may be just as safe and effective as standard medically prescribed low fat diets for losing weight and if continued beyond the weight loss target, may confer long term health benefits. A particularly noteworthy feature of the study is the high proportion of participants who stuck to the diets for the whole 2 years: 85 per cent.
The study was led by researchers from Ben-Gurion University of the Negev (BGU) in Israel and is published in the 17th July issue of the New England Journal of Medicine, NEJM. Other members of the study team came from Nuclear Research Center in Dimona, Israel, Harvard University, Boston, US, The University of Leipzig, Germany and the University of Western Ontario, Canada.
The authors wrote that one of the main difficulties of assessing the safety and effectiveness of weight loss diets is that trials usually have a high drop out rate and don’t last long enough.
For this 2 year trial, they intensively monitored 322 moderately obese adults of mean age 52 years, and mean BMI (body mass index) of 31 that had been randomly assigned to one of three diets: low-fat, restricted-calorie; Mediterranean, restricted-calorie; or low-carbohydrate, non-restricted-calorie. 86 per cent of the participants were men.
The trial was conducted at the Nuclear Research Center in Israel and “involved unparalleled and significant cooperation between staff, participants and their spouses”, said the authors in a press statement.
The workplace cafeterias underwent a sort of “health revolution” to provide the right foods for each of the three diets and to integrate easily with clinical requirements. For example, dishes were clearly labelled using different colours for each diet, and participants and their spouses had nutritional counselling and education on how to stick to the diets not only at work but also at home.
The participants also filled in electronic questionnaires developed specifically for the study.
The results showed that:
- 95.4 per cent of the participants stuck to their diets for at least 1 year and 84.6 per cent for the whole 2 years.
- The group on the Mediterranean diet consumed the most dietary fiber and had the highest ratio of monounsaturated to saturated fat intake.
- The low carbohydrate group ate the least carbohydrates and the most fat, protein and cholesterol and had the highest proportion of members with ketones in their urine.
- The average weight loss was: 2.9 kg (6.4 lbs) in the low fat diet group; 4.4 kg (9.7 lbs) in the Mediterranean diet group; and 4.7 kg (10.4 lbs) in the low carbohydrate group.
- The average weight loss was greater among the 272 participants who kept to the diets for the whole 2 years: 3.3 kg (7.3 lbs) in the low fat, 4.6 kg (10.1 lbs) in the Mediterranean, and 5.5 kg (12.1 lbs) in the low carbohydrate groups.
- The relative reduction in total cholesterol to high-density lipoprotein cholesterol (the so called “good” cholesterol) ratio was 20 per cent in the low carbohydrate group and 12 per cent in the low fat group.
- Among the 36 participants with diabetes, more favourable levels in fasting plasma glucose and insulin were reached by those on the Mediterranean diet than those on the low fat diet.
- Liver function and inflammatory biomarkers improved in all three diets.
The authors concluded that:
“Mediterranean and low-carbohydrate diets may be effective alternatives to low-fat diets. The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal preferences and metabolic considerations might inform individualized tailoring of dietary interventions.”
Lead author Dr Iris Shai, a researcher at the S. Daniel Abraham International Center for Health and Nutrition in the Department of Epidemiology at BGU, said that the weight loss achieved by all the diets were “comparable to results from physician-prescribed weight loss medications”.
Shai said that “clearly, there is not one diet that is ideal for everyone”.
“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,” she added.
The authors acknowledged that one limitation of the study was the low percentage of women (14 per cent).
“Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet.”
Shai, Iris, Schwarzfuchs, Dan, Henkin, Yaakov, Shahar, Danit R., Witkow, Shula, Greenberg, Ilana, Golan, Rachel, Fraser, Drora, Bolotin, Arkady, Vardi, Hilel, Tangi-Rozental, Osnat, Zuk-Ramot, Rachel, Sarusi, Benjamin, Brickner, Dov, Schwartz, Ziva, Sheiner, Einat, Marko, Rachel, Katorza, Esther, Thiery, Joachim, Fiedler, Georg Martin, Bluher, Matthias, Stumvoll, Michael, Stampfer, Meir J., the Dietary Intervention Randomized Controlled Trial (DIRECT) Group.
N Engl J Med Volume 359, Number 3, pages 229-241, July 17, 2008.
Sources: Journal abstract, American Associates, Ben-Gurion University of the Negev press statement.
Written by: Catharine Paddock,