Does obesity cause low testosterone?

Most men know that carrying extra weight raises their risk of type 2 diabetes, heart disease, and stroke. Fewer know what it does to their testosterone.

In England, 70% of men are now overweight, and 29% are living with obesity.¹ For a lot of those men, low testosterone is part of the picture. It also works in reverse: when men lose weight, testosterone tends to climb back up.

Here’s what the research shows.

The link between obesity and low testosterone

Testosterone shapes a lot of male health: muscle mass, bone density, sex drive, mood, and energy. Carrying excess fat interferes with nearly all of it.

The main mechanism is an enzyme called aromatase, which sits in fat tissue and converts testosterone into oestrogen. The more fat tissue you carry, the more of your testosterone gets converted. Men produce oestrogen normally and need some of it, but the balance matters. As testosterone falls and oestrogen rises, the knock-on effects can include weaker erections, lower libido, breast tissue development, and further weight gain, which feeds the same loop.

Waist size is a useful marker here. A waist over 102 cm (40 inches) is one of the recognised thresholds for raised metabolic risk in men, and the larger the waist, the more likely testosterone is to be low.² Current NHS guidance is simpler again: keep your waist to less than half your height.

Excess weight also drives insulin resistance, where your cells stop responding properly to insulin. That’s a primary route into type 2 diabetes, which has its own two-way relationship with low testosterone, and it disrupts the hormonal signalling that tells your testes to produce testosterone in the first place.²

What does the research say?

A study at the University at Buffalo compared 25 young men with obesity against 25 lean peers, all aged 14 to 20. Those with obesity had up to 50% less total testosterone, even after the researchers controlled for age and stage of puberty.³ Low testosterone isn’t only an older man’s problem.

A larger analysis of 1,849 men found that around 40% of men with obesity had low testosterone, and that the risk climbed as body mass index (BMI) climbed.⁴

Poor sleep makes the picture worse on both sides, and losing weight tends to improve how well you sleep.

Does losing weight increase testosterone?

The evidence says yes, and it’s stronger than most of the other natural methods of raising testosterone.

A systematic review and meta-analysis found that losing weight reliably reverses obesity-related low testosterone, and that the size of the effect tracks the size of the weight loss. A low-calorie diet raised total testosterone by around 2.9 nmol/L on average, while bariatric surgery, which produces much larger weight loss, raised it by around 8.7 nmol/L.⁵

You don’t need to be in the surgery category to see a change. Even smaller amounts of weight loss in men who are only mildly overweight have been linked to measurable rises in testosterone, and clinical guidance is to try weight loss and exercise first for an overweight man with low testosterone, ahead of any prescription.⁶

How much any individual sees will vary, and it depends on how much weight is lost and what else is going on with your health.

Can low testosterone cause weight gain?

The relationship runs both ways. Low testosterone is associated with more fat storage and less muscle mass, and it’s linked to a slower metabolic rate, poorer glucose control, and lower insulin sensitivity, all of which make weight gain more likely.²

Low testosterone can also disturb the balance of appetite hormones such as leptin and ghrelin, which may push appetite up.²

Over the longer term, men with low testosterone are more likely to develop metabolic syndrome, which refers to people who have type 2 diabetes, high blood pressure, and obesity together.²

Can testosterone therapy help with weight loss?

For men whose testosterone is genuinely low, treating it does appear to change body composition. A review of the evidence concluded that testosterone therapy increases lean body mass, reduces fat mass, and can produce sustained weight loss alongside reductions in waist circumference and BMI.⁷

The largest long-term dataset comes from an 11-year registry of men with low testosterone. Among those living with obesity, the men treated with testosterone lost an average of 23.2 kg, while the untreated men gained 4.2 kg.⁸ The same registry reported 34% of men with type 2 diabetes going into remission on long-term testosterone treatment.⁹

Two caveats matter. This is registry data rather than a randomised trial, so it can’t prove testosterone alone caused those results, and the treated men were also monitored closely for more than a decade. Also, testosterone replacement therapy isn’t licensed or recommended as a weight loss treatment. TRT is for men with diagnosed low testosterone, and the guidance is to address weight and lifestyle first.⁶

The first step either way is knowing where your levels actually sit.

The numan take

Obesity and low testosterone drive each other, which sounds bleak until you notice what it implies: progress on one side tends to move the other. Losing weight is associated with higher testosterone, and healthier testosterone can make it easier to build muscle and keep the weight off.

Start by finding out where you stand. Check your testosterone levels with a simple blood test, and if weight is the bigger issue, take a look at Numan’s weight loss treatments.

Note: Weight loss treatments aren’t suitable for everyone and are only prescribed following a clinical assessment. Individual results vary.

References:

^{1 NHS England. (2025). Health Survey for England 2024: Adults’ overweight and obesity. https://digital.nhs.uk/data-and-information/publications/statistical/health-survey-for-england/2024/adults-overweight-and-obesity}

^{2 Kelly, D. M., & Jones, T. H. (2015). Testosterone and obesity. Obesity Reviews. https://pubmed.ncbi.nlm.nih.gov/25982085/}

^{3 Mogri, M., Dhindsa, S., Quattrin, T., Ghanim, H., & Dandona, P. (2013). Testosterone concentrations in young pubertal and post-pubertal obese males. Clinical Endocrinology. https://pubmed.ncbi.nlm.nih.gov/22970699/}

^{4 Dhindsa, S., Miller, M. G., McWhirter, C. L., Mager, D. E., Ghanim, H., Chaudhuri, A., & Dandona, P. (2010). Testosterone concentrations in diabetic and nondiabetic obese men. Diabetes Care, 33(6), 1186–1192. https://doi.org/10.2337/dc09-1649}

^{5 Corona, G., Rastrelli, G., Monami, M., Saad, F., Luconi, M., Lucchese, M., Facchiano, E., Sforza, A., Forti, G., Mannucci, E., & Maggi, M. (2013). Body weight loss reverts obesity-associated hypogonadotropic hypogonadism: A systematic review and meta-analysis. European Journal of Endocrinology, 168(6), 829–843. https://doi.org/10.1530/EJE-12-0955}

^{6 Grossmann, M. (2011). Low testosterone in men with type 2 diabetes: Significance and treatment. The Journal of Clinical Endocrinology & Metabolism, 96(8), 2341–2353. https://doi.org/10.1210/jc.2011-0118}

^{7 Traish, A. M. (2014). Testosterone and weight loss: The evidence. Current Opinion in Endocrinology, Diabetes and Obesity, 21(5), 313–322. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4154787/}

^{8 Saad, F., Doros, G., Haider, K. S., & Haider, A. (2020). Differential effects of 11 years of long-term injectable testosterone undecanoate therapy on anthropometric and metabolic parameters in hypogonadal men with normal weight, overweight and obesity in comparison with untreated controls: Real-world data from a controlled registry study. International Journal of Obesity, 44(6), 1264–1278. https://doi.org/10.1038/s41366-019-0517-7}

^{9 Haider, K. S., Haider, A., Saad, F., Doros, G., Hanefeld, M., Dhindsa, S., Dandona, P., & Traish, A. (2020). Remission of type 2 diabetes following long-term treatment with injectable testosterone undecanoate in patients with hypogonadism and type 2 diabetes: 11-year data from a real-world registry study. Diabetes, Obesity and Metabolism. https://doi.org/10.1111/dom.14122}