In addition to growth hormone (GH), sex hormones are important determinants of body composition. Aging is accompanied by a decrease in free testosterone levels and, as BMI as well as fat mass increase with age (with a redistribution of body fat), whereas muscle mass decreases, it is tempting to attribute a causal role to the decrease in androgen levels. In our study involving 372 males aged >20-85, age was found to be positively correlated with BMI and fat mass as measured by impedance, and negatively correlated with levels of free testosterone and free insulin-like growth factor-I. Multiple regression analysis revealed that BMI and age were independent determinants of testosterone levels. The latter decreased from 598+/-188 (SD) ng/dl in the young controls to 453+/-161 ng/dl in the elderly group, free testosterone decreasing from 15.35+/-4.10 to 8.38+/-2.51 ng/dl. Fat-free mass decreased by 18.9%. In a subgroup of 57 men aged 70-80 years, testosterone levels correlated negatively with percentage body fat (r=-0.57), abdominal fat (r=-0.56) and plasma insulin levels (r=-0.40). As GH levels and pulsatility also decrease with age and as, moreover, androgens amplify endogenous secretion of GH, it is not easy to determine the relative role of androgen deficiency in the age-associated changes in body composition. Moreover, increase in fat mass (obesity), as occurs in aging males, is in itself associated with low levels of free testosterone and GH which both normalize after weight reduction. The role of testosterone in the age-associated changes in body composition is, however, further suggested by the increase in lean body mass and in mid-arm circumference and the decrease in waist-to-hip ratio observed after testosterone treatment of elderly men with decreased testosterone levels. Also in healthy eugonadal men, testosterone treatment, at least in supraphysiological doses, causes an important increase in fat-free mass (+/-10%) and in muscle size. The changes in muscle volume are associated with an increase in muscle fibre diameter, suggesting that testosterone induces muscle cell hypertrophy. In conclusion, aging in males is accompanied by an important increase in fat mass and a decrease in lean body mass. Several indices of body composition are significantly correlated with plasma testosterone levels before and after correction for BMI and age. It is evident, however, that in addition to testosterone levels, the age-associated somatopause is also a determinant of the changes in body composition.
As men age, serum testosterone concentrations decrease, the percentage of body mass that is fat increases, the percentage of lean body mass decreases, and muscle strength decreases. Because these changes are similar to those that occur in hypogonadal men, we hypothesized that increasing the serum testosterone concentration of men over 65 yr of age to that in young men would decrease their fat mass, increase their lean mass, and increase their muscle strength.
We randomized 108 men over 65 yr of age to wear either a testosterone patch or a placebo patch in a double blind study for 36 months. We measured body composition by dual energy x-ray absorptiometry and muscle strength by dynamometer before and during treatment. Ninety-six men completed the entire 36-month protocol.
Fat mass decreased (−3.0 ± 0.5 kg) in the testosterone-treated men during the 36 months of treatment, which was significantly different (P = 0.001) from the decrease (−0.7± 0.5 kg) in the placebo-treated men. Lean mass increased (1.9 ± 0.3 kg) in the testosterone-treated men, which was significantly different (P < 0.001) from that (0.2 ± 0.2 kg) in the placebo-treated men. The decrease in fat mass in the testosterone-treated men was principally in the arms (−0.7 ± 0.1 kg; P < 0.001 compared to the placebo group) and legs (−1.1 ± 0.2 kg; P < 0.001), and the increase in lean mass was principally in the trunk (1.9 ± 0.3 kg; P < 0.001). The change in strength of knee extension and flexion at 60° and 180° angular velocity during treatment, however, was not significantly different between the two groups. We conclude that increasing the serum testosterone concentrations of normal men over 65 yr of age to the midnormal range for young men decreased fat mass, principally in the arms and legs, and increased lean mass, principally in the trunk, but did not increase the strength of knee extension and flexion, as measured by dynamometer.
One thing to keep in mind here is that T supplementation increased lean mass and decreased fat mass without exercise. Just imagine what it would do with some. One study I read stated that the increase in lean mass in T supplementation (again, without exercise) was on the order of 10%, although that wasn’t seen in the above study.