The nutrient goals for the four diet groups were: 20% fat, 15% protein, and 65% carbohydrates (low-fat, average-protein); 20% fat, 25% protein, and 55% carbohydrates (low-fat, high-protein); 40% fat, 15% protein, and 45% carbohydrates (high-fat, average-protein); and 40% fat, 25% protein, and 35% carbohydrates (high-fat, high-protein). Thus, two diets were low-fat and two were high-fat, and two were average-protein and two were high-protein, constituting a two-by-two factorial design. The four diets also allowed for a dose–response test of carbohydrate intake that ranged from 35 to 65% of energy. Other goals for all groups were that the diets should include 8% or less of saturated fat, at least 20 g of dietary fiber per day, and 150 mg or less of cholesterol per 1000 kcal. Carbohydrate-rich foods with a low glycemic index were recommended in each diet. Each participant’s caloric prescription represented a deficit of 750 kcal per day from baseline, as calculated from the person’s resting energy expenditure and activity level.
Blinding was maintained by the use of similar foods for each diet. Staff and participants were taught that each diet adhered to principles of a healthful diet29 (link) and that each had been recommended for long-term weight loss, thereby establishing equipoise.1 (link),2 (link),26 (link) Investigators and staff who measured outcomes were unaware of the diet assignment of the participants.
Group sessions were held once a week, 3 of every 4 weeks during the first 6 months and 2 of every 4 weeks from 6 months to 2 years; individual sessions were held every 8 weeks for the entire 2 years. Daily meal plans in 2-week blocks were provided (see theSupplementary Appendix ). Participants were instructed to record their food and beverage intake in a daily food diary and in a Web-based self-monitoring tool that provided information on how closely their daily food intake met the goals for macronutrients and energy. Behavioral counseling was integrated into the group and individual sessions to promote adherence to the assigned diets. Contact among the groups was avoided.
The goal for physical activity was 90 minutes of moderate exercise per week. Participation in exercise was monitored by questionnaire30 (link) and by the online self-monitoring tool.
Blinding was maintained by the use of similar foods for each diet. Staff and participants were taught that each diet adhered to principles of a healthful diet29 (link) and that each had been recommended for long-term weight loss, thereby establishing equipoise.1 (link),2 (link),26 (link) Investigators and staff who measured outcomes were unaware of the diet assignment of the participants.
Group sessions were held once a week, 3 of every 4 weeks during the first 6 months and 2 of every 4 weeks from 6 months to 2 years; individual sessions were held every 8 weeks for the entire 2 years. Daily meal plans in 2-week blocks were provided (see the
The goal for physical activity was 90 minutes of moderate exercise per week. Participation in exercise was monitored by questionnaire30 (link) and by the online self-monitoring tool.
