Testosterone is often discussed in relation to muscle, sex drive and male reproductive health. Its role goes much further than that.

For men, testosterone also has a close relationship with body composition and metabolic health. Higher levels of body fat are associated with lower testosterone, while low testosterone can make it easier to gain fat and harder to maintain muscle mass.

That creates a two-way relationship. Obesity can contribute to lower testosterone, while testosterone deficiency can contribute to changes in body composition that make weight management harder.

Understanding this relationship can help explain why weight management is sometimes more complex than calorie intake and physical activity alone.

Why carrying extra weight can affect testosterone

Body fat does far more than sit under the skin. It is active tissue that produces hormones and influences how other hormones behave.

As body fat increases, testosterone production can be affected. Men with obesity are more likely to have lower testosterone levels than men within a healthier weight range. The effect tends to become stronger as the amount of excess weight increases.

One reason involves an enzyme called aromatase. Fat tissue contains aromatase, which converts some testosterone into oestradiol, a type of oestrogen. Having more fat tissue can increase this conversion.

Excess weight can also affect the hormonal signals between the brain and the testes. Those signals help regulate testosterone production. Changes in insulin levels and inflammation linked to obesity may also interfere with normal hormone function.

There is another piece of the puzzle. Men with obesity often have lower levels of a protein called sex hormone-binding globulin, or SHBG. SHBG carries sex hormones through the bloodstream.

Lower SHBG can reduce the amount of testosterone measured in a blood test without necessarily meaning that testosterone production has stopped working properly. Doctors may therefore look at free testosterone, symptoms and other test results before deciding whether low testosterone is present.

Low testosterone can change where the body stores fat

The relationship also runs in the opposite direction.

Testosterone helps maintain muscle tissue and influences body composition. When testosterone levels are low, men can lose some muscle mass while gaining body fat, particularly around the abdomen.

That shift can have consequences for weight management. Muscle tissue uses energy, so having less muscle can affect how many calories the body burns at rest. Low testosterone has also been associated with increased body fat and changes in insulin sensitivity.

None of that means low testosterone automatically leads to obesity.

Sleep, eating habits, physical activity, age, genetics, medications and other health conditions all influence body weight. Hormones form one part of a much bigger picture.

Still, for a man who has both excess weight and low testosterone, the two can reinforce each other.

Can losing weight raise testosterone?

For men with obesity, weight reduction can improve testosterone levels.

Research has found that weight loss is associated with an increase in testosterone. This can happen because reducing excess fat may improve the hormonal and metabolic processes that have been affected by obesity.

European urology guidance recommends weight reduction and lifestyle changes as the first approach for men with obesity and functional hypogonadism. Evidence from dietary and physical activity interventions shows that testosterone can rise after weight reduction, although the increase may be modest.

The amount of weight loss can also influence the hormonal response. More substantial weight reduction has been associated with greater improvements in testosterone than smaller changes. Research in men undergoing bariatric surgery has shown that substantial weight loss can restore activity within the hormonal system responsible for testosterone production.

This is one reason weight management can form part of the treatment plan when obesity and low testosterone occur together.

What about testosterone replacement?

Testosterone replacement therapy, often called TRT, may be appropriate for some men with confirmed testosterone deficiency and relevant symptoms. It is not a general weight loss treatment.

Clinical evidence suggests that testosterone treatment can reduce fat mass and increase lean mass in some men with confirmed hypogonadism. However, studies have not consistently shown that testosterone treatment produces substantial weight loss.

TRT also requires medical assessment. A clinician needs to consider the cause of low testosterone, fertility plans, existing health conditions and potential risks before treatment begins. Guidelines recommend investigating the cause of testosterone deficiency and addressing obesity and related health conditions as part of the wider management plan.

For some men, improving weight, sleep, physical activity and other health factors may raise testosterone without hormone replacement. For others with persistent, symptomatic deficiency, testosterone treatment may form part of their care.

What this means if weight and testosterone are both concerns

The relationship between testosterone and obesity is a two-way street, but it is not a simple one.

A man can have obesity without testosterone deficiency. He can also have low testosterone for reasons that have little to do with his weight. In some cases, however, the two problems can reinforce each other.

If changes in weight are accompanied by symptoms associated with low testosterone, it is sensible to speak to a healthcare professional. A proper assessment can help establish whether hormones are part of the picture and what may be affecting them.

That is why looking at only the scales can miss part of the picture. Likewise, treating a testosterone result without considering weight, metabolic health and the reason for the low level may miss an opportunity to address what is happening more broadly.

For many men, that is a more productive place to start than assuming the problem has a single cause. Once the contributing factors are understood, treatment can be shaped around the person rather than a single number on a blood test.

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