Yes, low testosterone can reverse weight loss. One study that looked at the relationship between obesity in men and testosterone deficiency shows that testosterone therapy produces sustained weight loss without recidivism (reverting to previous weight). On average, men with a higher body mass index (BMI) have lower levels of testosterone, and men with lower levels of testosterone have a higher BMI (overweight or obese). Therefore, if a man is at a healthy weight and then experiences a drop in testosterone levels, he is more likely to gain weight. Likewise, if a man is overweight or obese and experiences an increase in his testosterone levels, he is more likely to lose weight more easily. In general, the physiological process that the male body undergoes when body fat is increased involves: • Put on extra body fat — Extra weight is gained, either through improper diet, lack of exercise, or both • Increases cortisol/fat cell aromatization — An increase is seen in the level of aromatase in fat cells, which causes testosterone to be more readily converted to estrogen (estradiol) • Lower testosterone — The body experiences lower levels of testosterone • Further lower human growth hormone — Human growth hormone (HGH) levels are also negatively impacted