Losing Weight--And Not Finding It Again
The February 26, 2009 issue of the New England Journal of Medicine published an article comparing four diets: 1) 20 percent fat, 15 percent protein and 65 percent carbohydrates (low-fat, average-protein); 2) 20 percent fat, 25 percent protein and 55 percent carbohydrates (low-fat, high-protein); 3) 40 percent fat, 15 percent protein and 45 percent carbohydrates (high-fat, average-protein); and 4) 40 percent fat, 25 percent protein and 35 percent carbohydrates (high-fat, high-protein). Goals for all groups were that the diets should include 8 percent or less of saturated fat, at least 20 g of dietary fiber per day and 150 mg or less of cholesterol per 1,000 kcal. Carbohydrate-rich foods with a low glycemic index were recommended in each diet (e.g., fruits, vegetables, whole grains and legumes). Each participant's caloric prescription represented a decrease of 750 kcal per day from base line resting metabolic rate.
Group discussion sessions were held once a week, three of every four weeks during the first six months and two of every four weeks from six months to two years; individual sessions were held every eight weeks for the entire two years. Daily meal plans in two-week blocks were provided. The goal for physical activity was 90 minutes of moderate exercise per week. Participation in exercise was monitored by questionnaire and by the online self-monitoring tool.
The amount of weight loss after two years was similar in participants assigned to a diet with 25 percent protein and those assigned to a diet with 15 percent protein. Weight loss was the same in those assigned to a diet with 40 percent fat and those assigned to a diet with 20 percent fat. There was no effect on weight loss of carbohydrate level through the target range of 35 to 65 percent; the change in waist circumference did not differ significantly among the diet groups.
All the diets reduced risk factors for cardiovascular disease and diabetes at six months and two years. The metabolic syndrome was present in 32 percent of the participants at baseline, and the percentage was lower at two years, ranging from 19 to 22 percent in the four diet groups. Attendance at group sessions strongly predicted weight loss at 2 years (0.2 kg for every session attended) and was similar among the diet groups.