From the standpoint of promoting leanness, exercise is of most value if oxidation of stored fat is maximized during and following the exercise sessions. Bahadori has proposed that this can best be achieved if prolonged exercise of moderate intensity is performed during a 12-14 h "mini-fast" that entails skipping a meal; if subsequent food consumption features low-fat foods, the fat stores expended during and after the exercise will not be fully repleted by dietary fat. Thus, prolonged compliance with such a regimen should lead to steady loss of body fat until a much leaner equilibrium body composition is attained. The feasibility and efficacy of this strategy has been examined in an open pilot study. Participants were asked to perform prolonged, moderate-intensity aerobic exercise at least 3-5 times weekly, nesting each exercise session within a 12-14 h mini-fast. No restrictions were placed on daily calorie consumption, but low-fat, low-glycemic-index food choices were recommended. Of the 34 subjects originally enrolled, 27 returned for follow-up evaluations at 6 and 12 weeks. During the 12 week study, the average fat loss in these 27 subjects - 7.4 kg - corresponded to one-quarter of their baseline fat mass. Fasting insulin levels likewise fell by 25%. The rate of fat loss was at least as great in the second 6 weeks as in the first, suggesting that fat loss might have persisted for some time if the study had been prolonged. This protocol, combining elements of exercise training, fasting, and low-fat eating, is both sustainable and healthful, and in reasonably compliant subjects may have considerable potential for promoting and maintaining leanness and insulin sensitivity.