Testosterone promotes muscle growth. Simultaneously, it may suppress fat gain. As a result, some testosterone-deficient men tend to gain fat more easily than men who are at a healthy weight. Obese men have 30% lower testosterone levels on average when compared to those who are a normal weight. More than 70% of morbidly obese men suffer from testosterone deficiency, or male hypogonadism, a disorder characterized by abnormally low levels of testosterone. Male hypogonadism may reverse with weight loss. In simplest terms, excessive belly fat appears to suppress testosterone levels, which, in turn, leads to more weight gain. To explain things further, a decrease in testosterone levels leads to an increase in body fat. The reverse is true as well: when putting on additional weight, testosterone levels decrease.