Physical Activity Level and Dietary Intake Associated with Fat-Free Muscle Mass Changes During Intentional Weight Loss in Overweight and Obese Subjects

Background: The prevalence of obesity and related complications is increasing relentlessly worldwide. The effect of intentional weight loss strategies for obese individuals on fat-free muscle mass (FFMM) and metabolic and general health is not well known. The aim of this research is to measure the effects of dietary intake and physical activity level on FFMM change during intentional weight loss in obese subjects. Materials and Methods: Nine hundred and sixty-five overweight and obese community free-living subjects had the effects of physical activity level and dietary intake on FFMM change during intentional weight loss assessed in a prospective longitudinal study. Anthropometric, physical activity, dietary intake, inflammatory markers, and oxidative damage were assessed at baseline and follow-up. Validated questionnaires were used to measure dietary intake and physical activity. We compared FFMM loss or gain between subjects stratified by calorie, protein, and fruit and vegetable intake and physical activity levels. The Cox proportional hazards analysis was used to determine the independent effects of dietary intake and physical activity on FFMM changes. Results: A total of 965 subjects [(mean (SD) age 39 ± 12 years, 801 (83%)] females] were assessed at baseline with follow-up for a period of 427 ± 223 days. Using the WHO criteria for body mass index (BMI), 284 (30%) subjects were found to be overweight and 584 (62%) were obese. We found significant correlations between fat–muscle mass ratio (FMR) and inflammatory and oxidative damage markers. After adjusting for important prognostic indicators, age, gender, occupation, physical activity, and fruit and vegetable consumption were found to be significantly associated with FFMM at baseline (p < 0.05). We found no statistically significant difference in dietary protein or amino acids intake in subjects who gained FFMM compared to those who lost FFMM both at baseline and follow-up. By contrast, high consumption of fruits and vegetable and increased calorie intake were associated with increased odds of FFMM gain (p < 0.05). Increased physical activity was independently associated with significant FFMM gain after adjusting for other important indicators ([hazard ratio (95% CI): 0.49 (0.25, 0.97); p = 0.039]. Conclusions: Increased physical activity and high calorie, fruit and vegetable intake are associated with FFMM preservation or gains during intentional weight loss in obese subjects.