As blogged previously, there are many medications that need to be considered for monitoring and potential adjustment during a weight loss journey. Another one to add to the list is testosterone.

As blogged previously, it is common for men with obesity to have low testosterone levels. When weight is elevated, the brain often turns down the signals telling the testicles to make testosterone (called central hypogonadism). Men of any body size can have low testosterone levels due to other conditions as well (eg a primary testicular issue, or other causes of central hypogonadism).

All men on testosterone need to have their testosterone levels monitored to ensure they are on the right amount. Too much testosterone comes with health risks including overproduction of red blood cells (elevated hemoglobin or hematocrit, which increases risk of a cardiovascular event or blood clot), increased risk of prostate enlargement/cancer, and others.

When a man on testosterone with obesity starts a weight loss treatment, a number of things happen that can affect testosterone levels, including:

  • Central hypogonadism due to obesity may improve/recover with weight loss, meaning that his body may want to increase its own testosterone production. However, if a full replacement dose of testosterone is continued, the testicles’ production of testosterone will not have the chance to ‘wake up’, because the testosterone treatment will suppress the testicular testosterone production.
  • A smaller body may not need as much testosterone to maintain normal levels.
  • The protein that binds to testosterone in the blood, called the sex hormone binding globulin (SHBG) is typically low in men with obesity, and often increases as weight goes down. This could result in lower levels of free circulating testosterone, and it is this free testosterone that has the clinical effects.

So where this all pans out in each individual is difficult to predict. For men with central hypogonadism due to obesity, the only way to know if the natural testosterone production will ‘wake up’ is to gradually reduce the testosterone dosage to see if free testosterone levels (free androgen index) will stay normal, with continued gradual reduction of dose and measurement of testosterone levels to see if the testosterone treatment can be weaned off completely. It’s important that all men taking testosterone and losing weight have their testosterone levels and blood counts monitored with weight loss to ensure their free testosterone levels stay normal and their hemoglobin/hematocrit do not become elevated. Ensuring good hydration is especially important as dehydration can increase hematocrit as well.

BOTTOM LINE: Men taking testosterone need to have levels of testosterone as well as CBC (blood counts) monitored closely during weight loss. For men taking testosterone because of central hypogonadism (most common reason), attempts should be made to decrease the testosterone dose to determine whether endogenous (testicular) production of testosterone recovers with weight loss.

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