A recent study published in the Journal of the American Medical Association (JAMA) sought to determine whether 5α-reduction of testosterone to dihydrotestosterone (DHT) is required for promotion of fat-free body mass. The 5α-Reductase Trial was a parallel-group, double-blind, randomized placebo-controlled trial of 139 men ages 18 to 50 who were given varying doses of testosterone enanthate plus placebo or dutasteride. The primary outcomes measured were changes in fat-free body mass, muscle strength, sexual function, prostate volume, and hematocrit and serum lipid levels.
One hundred and two men completed the 20-week intervention. Ultimately, statistically significant changes in the aforementioned primary outcome categories was unchanged between study groups. This trial suggests that conversion of testosterone to DHT is not necessary for mediating anabolic effects on muscle to minimize body fat composition. This data is similar to previous studies that have reported no significant effects of 5α-reductase inhibition on muscle or bone mass.
Reference: Bhasin S, Travison TG, Storer TW, et al. Effect of testosterone supplementation with and without a dual 5α-reductase inhibitor on fat-free mass in men with suppressed testosterone production. JAMA 2012;307(9):931-940.