The more testosterone you give men, the more fat they lose. Canadian and American endocrinologists describe the effect of a study in which they gave fifty healthy men different doses of testosterone enanthate [see structure below] for twenty weeks.
Testosterone increases fat-free mass, and therefore also muscle mass. More muscle mass also often means less fat mass, as muscles consume more energy. The effects of testosterone therapy on body composition are well known. But are these effects the same in all parts of the body? This is the question the researchers set out to answer – especially for fat mass. To do this they gave healthy men aged 18-35 a weekly injection of 25, 5-, 125, 300 or 600 mg of testosterone enantate for a period of twenty weeks. They also gave the men a GnRH-agonist that deactivated their own testosterone production.
The weekly doses of 25 and 50 mg testosterone enantate resulted in a lower than normal testosterone level. The 125 mg dose resulted in a more or less normal level, while 300 and 600 mg took the subjects up to supraphysiological levels.
The higher the dose, the more lean body mass the men built up. Lean body mass, or fat free mass, consists of fluid, blood mass, bone mass and muscle mass.
The doses that resulted in below-normal levels of testosterone also resulted in more fat tissue. The supraphysiological doses on the other hand led to a disappearance of fat.
A low testosterone level encourages fat deposition in the abdominal area. Supraphysiological doses prevent fat from accumulating in the abdominal area, but only reduce the quantity of fat by a small amount. This applies to both subcutaneous fat and deeper abdominal fat.
The supraphysiological doses do decrease the amount of fat on the limbs, however. In particular, intramuscular fat is reduced.
The researchers did not examine how high doses of testosterone reduce the amount of fat. They speculate that testosterone sabotages the enzymes responsible for fat cells taking up fatty acids and inhibits the development of young fat cells.
Dose-Dependent Effects of Testosterone on Regional Adipose Tissue Distribution in Healthy Young Men
Testosterone supplementation reduces total body adipose tissue (AT), but we do not know whether the effects are uniformly distributed throughout the body or are region specific, or whether they are dose related.
We determined the effects of graded doses of testosterone on regional AT distribution in 54 healthy men (18–35 yr) in a 20-wk, randomized, double-blind study of combined treatment with GnRH agonist plus one of five doses (25, 50, 125, 300, or 600 mg/wk) of testosterone enanthate (TE). Total body, appendicular, and trunk AT and lean body mass were measured by dual-energy x-ray absorptiometry, and sc, intermuscular, and intraabdominal AT of the thigh and abdomen were measured by magnetic resonance imaging. Treatment regimens resulted in serum nadir testosterone concentrations ranging from subphysiological to supraphysiological levels. Dose-dependent changes in AT mass were negatively correlated with TE dose at all sites and were equally distributed between the trunk and appendices. The lowest dose was associated with gains in sc, intermuscular, and intraabdominal AT, with the greatest percent increase occurring in the sc stores. At the three highest TE doses, thigh intermuscular AT volume was significantly reduced, with a greater percent loss in intermuscular than sc depots, whereas intraabdominal AT stores remained unchanged. In conclusion, changes in testosterone concentrations in young men are associated with dose-dependent and region-specific changes in AT and lean body mass in the appendices and trunk. Lowering testosterone concentrations below baseline increases sc and deep AT stores in the appendices and abdomen, with a greater percent increase in sc depots. Conversely, elevating testosterone concentrations above baseline induces a greater loss of AT from the smaller, deeper intermuscular stores of the thigh.