Importance: Obesity is strongly associated with low testosterone levels in men. Whether testosterone treatment has benefits on body composition over and above caloric restriction is unknown.
Objective: To determine whether testosterone treatment augments diet-induced loss of fat mass and prevents loss of muscle mass.
Design: Randomised double-blind, placebo-controlled trial.
Participants: Obese men with total testosterone <12nmol/L.
Intervention: 100 participants receiving 10 weeks of a very low energy diet (VLED) followed by weight maintenance were randomised at baseline to 56 weeks of intramuscular testosterone undecanoate (n=49, cases) or placebo (n=51, controls).
Main Outcomes: The primary outcome was the between-group difference in fat mass at study end (56 weeks), quantified by dual-energy X-ray absorptiometry (DXA). Other main outcomes: change in lean mass, visceral fat and body weight.
Results: Cases and controls lost the same weight (testosterone -11.4kg; placebo -10.9kg) at study end (p=0.80). Cases had greater reductions in total fat, mean adjusted between-group difference (MAD) -2.9kg, p=0.04, and in visceral fat, MAD -2,678mm2, p=0.04. Although both groups lost the same lean mass following VLED (cases -3.9kg; controls -4.8kg, p=0.36), cases regained lean mass (3.3kg, p<0.001) during weight maintenance, in contrast to controls, 0.8kg, p=0.29 so at study end, cases had an attenuated reduction in lean mass compared to controls, MAD 3.4kg, p=0.002.
Conclusions: Among obese men with lowered testosterone, testosterone treatment augmented diet-induced loss of total and visceral fat mass, and prevented diet-induced loss of lean mass. While men receiving placebo lost both fat and lean mass, the weight lost with testosterone treatment was almost exclusively due to loss of fat.
MNTF was supported by a postgraduate scholarship (1055305) and MG by a Career Development Fellowship (1024139) both from the NHMRC. BayerPharma provided testosterone, placebo and financial support to conduct investigations, but had no other role in the trial.