Cellular bioenergetics, work performance, body composition and psychological indices among women in a diet-exercise program

Forty moderately obese women enrolled in a 10 week study employing a low-fat, rotating energy diet, nutritional supplementation and aerobic walking. Energy intakes rotated between 2.09 and 6.27 MJ (500 and 1500 kcal) on alternate days. On 2.09 MJ days, women consumed meal substitute tablets each hour for the first eight hours of the day (totaling 24 gm carbohydrate, 4 gm fat, 3.2 gm protein), followed by whole food snacks and dinner. On 6.27 MJ days, subjects consumed diets of less than 20 percent fat and engaged in 20 to 30 minutes of aerobic walking. Nutrition supplements were taken daily, 34 women completed the study. Urinary ketones did not change throughout the study. Anthropometric and psychological parameters were measured at weeks 1,3 and 10. Body composition, assessed by bioelectrical impedance, showed mean declines in body weight of 5.8 kg (p<.001), body fat of 3.6 kg (p<.001), percent body fat of 2.4 percent (p<.001), and fat-free mass of 2.1 kg (p<.001). Improvements in reported sense of well-being (p<.01), perceived energy (p<.001) and body image (p<.001) were noted. Skeletal muscle energy function and work output was assessed using a computer-integrated arm ergometer and magnetic resonance spectroscopy to quantify the concentrations of inorganic phosphate (Pi), phosphocreatine (PCr) and intracellular pH (pHi) under resting and exercising conditions. Pre- to post-study increases in maximum arm strength (16.8 to 22.2 kg; pš.001) and total work output (191 to 282 joules; p<.001) were found. No changes over the study period were found in Pi/PCr ratios or pHi under either rest or exercise conditions. Although the impact of specific program components were not identified, the data suggest improved metabolic function in conjunction with favorable changes in psychological indices and body composition.