Effects of weight reduction rate on body composition, thyroid hormones and basal metabolic rate : A randomised controlled clinical trial

Background: Optimal body composition and body weight (BW) are important performance factors in sports that emphasize aesthetics and high power to weight ratio. Weight reduction guidelines for athletes per date suggest a weekly weight loss of 0.5-1.0 kg which corresponds to 0.7% and 1.4% of BW in a 70-kg athlete. Weight reduction may lead to loss of lean body mass (LBM) and changed thyroid hormone (TH) profile and thereby reduced basal metabolic rate (BMR). Combining energy restriction with resistance training may inhibit loss of LBM in obese subjects. Little is known about these changes and their effect on metabolism (BMR, TH) in athletes. Purpose: To compare changes in body composition, TH and BMR in two different weight-loss interventions promoting loss of 0.7% versus 1.4% of BW per week in elite athletes. Methods: 30 male and female elite athletes were randomized into slow weight reduction [ SLOW , n=14, 23.5 (3.3) y, 72.1 (12.2) kg] and fast weight reduction [ FAST , n=16, 22.3 (4.7) y, 72.2 (11.3) kg]. Both intervention groups included energy restricted diets and resistance training regimen for 4-12 weeks. The duration of the intervention was dependent on the desired weight loss and the type of intervention group the participant was allocated to. Diets were recorded at baseline by 4-day weighed food records which were used to design individual intervention diets promoting weekly BW loss of 0.7% or 1.4%. Four weekly resistance training sessions were added to the usual training regimen to stimulate muscle hypertrophy. The following measurements were taken at baseline and post intervention: BW, LBM, fat mass (FM) with dual energy x-ray absorptiometry (DEXA), serum thyroid stimulating hormone(s-THS) and free thyroxine (s-free T4) and BMR with indirect calorimeter. Results: There were no significant differences between the groups in any variables at the baseline. BW was reduced by 5.6 (3.0) % [mean(SD)], p<0.001 and 5.4 (2.3%), p<0.001) for SLOW- and FAST weight reduction group, respectively. The changes were not significantly different between the intervention groups (p=0.8). LBM was significantly increased for SLOW [2.0 (1.3) %, p<0.001] but not for FAST [1.1 (3.0) %, p=0.3]. There was a significant difference in FM reduction obtained during weight loss between the intervention groups SLOW -31 (2.9) %, p<0.001) and FAST -23.4 (13.8) %, p<0.001 (p=0.04). Free T4 reduction during the intervention was significant in FAST [-11.2 (7.6) %, p=0.001] but not in SLOW. These changes were significantly different between the groups (p