One year of caloric restriction in humans: Feasibility and effects on body composition and abdominal adipose tissue

Background. Caloric restriction (CR) increases maximal life span in short-lived organisms, and its effects are being explored in nonhuman primates. The objectives of this study were to determine the feasibility of prolonged CR in nonobese adults and to compare the effects of CR- and exercise-induced weight loss on body composition and abdominal adiposity. Methods. A randomized, controlled trial was conducted with 48 healthy, nonobese women and men, aged 57 ± 1 (mean ± standard error [SE]) years, with body mass index 27.3 ± 0.3 kg/m². Participants were randomly assigned to a 20% calorically-restricted diet (CR, n = 19), exercise designed to produce a similar energy deficit (EX, n = 19), or a healthy lifestyle control group (HL, n = 10) for 1 year. Assessments included weight, body composition by dual-energy x-ray absorptiometry, abdominal adipose tissue by magnetic resonance imaging, and energy intake by doubly labeled water. Results. The average level of CR achieved by the CR group was 11.5 ± 2.1%, and the EX group completed 59 ± 6.7% of their prescribed exercise. Weight changes were greater (p ≤ .0005) in the CR (-8.0 ± 0.9 kg) and EX (-6.4 ± 0.9) groups as compared to the HL group (-1.3 ± 0.9 kg), corresponding to reductions of 10.7%, 8.4%, and 1.7% of baseline weights, respectively. Whole-body fat mass and visceral and subcutaneous abdominal adipose tissue decreased significantly (p < .005) and comparably in the CR and EX groups, but did not change in the HL group. Conclusions. CR for 1 year was feasible, but the level of CR achieved was less than prescribed. CR and exercise were equally effective in reducing weight and adiposity.