A rigorously planned and executed research study didn’t surprise Atkins diet enthusiasts, as subjects on a low carbohydrate diet, similar to the Atkins diet, lost more weight than subjects on either the Mediterranean or low-fat diets. After two years, subjects in the low carb group lost an average of 4.7 kg (10.3 lbs); subjects in the Mediterranean-diet group lost 4.4 kg (9.7 lbs); and subjects in the low-fat group lost 2.9 kg (6.4 lbs).
Men lost more than women in the low carb group, losing 4.9 kg (10.8 lbs), and in the low fat group, 3.4 kg (7.5 lbs); in the Mediterranean-diet group, a little less, 4.0 kg (8.8 lbs).
As expected, subjects who stayed in the study the full two years lost even more: the low carb group lost 5.5 kg (12.1 lbs); the Mediterranean-diet group lost 4.6 kg (10.1 lbs); and the low fat group lost 3.3 kg (7.3 lbs).
The Low-Carbohydrate Diet
Calories were not restricted. The goal was to control carbohydrates—20 g a day for the first two months, then gradually increasing to 120 g a day. Participants were encouraged to select vegetables and avoid trans fats.
The Mediterranean Diet
Calories were restricted to 1800 kcal for men and 1500 kcal for women. The main source of fat calories were olive oil and five to seven nuts each day. The goal was to limit fat calories to 35% or less. The diet was rich in vegetables. Beef and lamb were replaced by fish and poultry.
The Low-Fat Diet
This diet was patterned after the American Heart Association recommendations. Calories were restricted to 1500 kcal each day for women, and 1800 kcal for men. Fat was restricted: only 30% of calories were from fats, and 10% from saturated fat. Cholesterol was limited to 300 mg per day. Subjects were encouraged to limit sweets and high fat snacks.
The Study
Three hundred twenty two subjects were enrolled in Israel. Subjects were overweight—the average BMI was 31. (For a person five feet six inches tall, this would be 87 kg [192 lbs]). People with kidney, liver or heart disease were excluded, as were pregnant women.
Subjects generally ate their midday meal on work days at the same cafeteria. Dieticians used signs to label selections that fit under each diet group. Subjects and their spouses received advice and counseling.
The study lasted two years, and had an extraordinarily high retention rate. While other studies had drop out rates often over 50%, in this study 95% stayed in the first year, and 85% stayed in the full two years.
Results
Besides the weight loss reported above, all subjects had an increase in HDL (the "good cholesterol"). LDL cholesterol levels varied widely. There was little change in the low-fat group, and trends down a little in the low carb, and a little more in the Mediterranean diet groups. Triglycerides fell in the low-carb group.
There was evidence of decreased insulin production in the Mediterranean group subjects who did not have diabetes. (Lower insulin is felt to be beneficial.) There was no change in blood glucose levels in subjects who did not have diabetes. Among those who did, only the Mediterranean diet group had lower (desirable) blood glucose levels.
Summary
The researchers pointed out that all three diets appear safe. Because participants using the low-carb diet did not have to count calories, that diet may be preferable for some. People with diabetes, heart disease, or other conditions, may want to choose a diet according to their particular needs. Before embarking on a diet, individuals should discuss options with their primary medical care provider.
The study was described in the July 17, 2008 issue of The New England Journal of Medicine, vol. 359, pgs. 229-241
