CONTEXT: The prevalence of severe obesity is increasing markedly, as is prevalence of comorbid conditions such as hypertension and type 2 diabetes mellitus; however, apart from bariatric surgery and pharmacotherapy, few clinical trials have evaluated the treatment of severe obesity. OBJECTIVE: To determine the efficacy of a weight loss and physical activity intervention on the adverse health risks of severe obesity. DESIGN, SETTING, AND PARTICIPANTS: Single-blind randomized trial conducted from February 2007 through April 2010 at the University of Pittsburgh. Participants were 130 (37% African American) severely obese (class II or III) adult participants without diabetes recruited from the community. INTERVENTIONS: One-year intensive lifestyle intervention consisting of diet and physical activity. One group (initial physical activity) was randomized to diet and physical activity for the entire 12 months; the other group (delayed physical activity) had the identical dietary intervention but with physical activity delayed for 6 months. MAIN OUTCOME MEASURES: Changes in weight. Secondary outcomes were additional components comprising cardiometabolic risk, including waist circumference, abdominal adipose tissue, and hepatic fat content. RESULTS: Of 130 participants randomized, 101 (78%) completed the 12-month follow-up assessments. Although both intervention groups lost a significant amount of weight at 6 months, the initial-activity group lost significantly more weight in the first 6 months compared with the delayed-activity group (10.9 kg (95% confidence interval (CI) 9.1 to 12.7) versus 8.2 kg (95% CI 6.4 to 9.9), p = 0.02 for group x time interaction). Weight loss at 12 months, however, was similar in the 2 groups (12.1 kg (95% CI 10.0 to 14.2) versus 9.9 kg (95% CI 8.0 to 11.7), p = 0.25 for group x time interaction). Waist circumference, visceral abdominal fat, hepatic fat content, blood pressure, and insulin resistance were all reduced in both groups. The addition of physical activity promoted greater reductions in waist circumference and hepatic fat content. CONCLUSION: Among patients with severe obesity, a lifestyle intervention involving diet combined with initial or delayed initiation of physical activity resulted in clinically significant weight loss and favorable changes in cardiometabolic risk factors. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT00712127.

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