Exercise Preserves Lean Mass During Weight Loss

Calorie restriction alone typically leads to significant lean mass losses, with studies indicating losses of 20-30% in the absence of exercise. Incorporating exercise reduces these losses by approximately half. The 'quarter fat-free mass loss' rule often applies mainly to non-exercising individuals. Weight loss affects daily energy expenditure, with lean and fat mass losses contributing 19 and 4.5 calories per kilogram per day, respectively. As body weight decreases, less energy is required for movement, leading to an additional estimated reduction of 30 calories in total daily energy expenditure per kilogram lost. Further reductions in resting energy expenditure may indicate metabolic adaptation resulting from hormonal and cellular changes aimed at maintaining energy balance.