Obesity is an important and potentially reversible cause of functional secondary hypogonadism in men. This condition is often referred to as male obesity-related secondary hypogonadism (MOSH). It is characterised by impaired function of the hypothalamic–pituitary–testicular axis, resulting in reduced testosterone production without primary structural failure of the testes.
Men with obesity frequently have lower total testosterone concentrations. This is partly explained by reduced levels of sex hormone-binding globulin (SHBG), although free testosterone may also be decreased in more severe cases. The prevalence of biochemical testosterone deficiency increases with the severity of obesity, but estimates vary considerably depending on the population studied and the diagnostic criteria applied.
Typical symptoms and clinical consequences may include:
These symptoms are not specific to testosterone deficiency and may also result from obesity, obstructive sleep apnoea, diabetes, depression, medication use or other chronic illnesses. Hypogonadism should therefore not be diagnosed on the basis of symptoms alone.
The Hypothalamic–Pituitary–Testicular Axis
Under normal physiological conditions, kisspeptin-producing neurons stimulate gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. GnRH subsequently stimulates the pituitary gland to release luteinising hormone (LH) and follicle-stimulating hormone (FSH).
LH binds to receptors on the Leydig cells of the testes and stimulates testosterone production. FSH acts primarily on the Sertoli cells and, together with intratesticular testosterone, supports spermatogenesis.
This image was created using artificial intelligence.
Hypogonadotropic hypogonadism and the kisspeptin pathway
How Obesity Contributes to Low Testosterone
Obesity and testosterone deficiency may reinforce one another. Several mechanisms are involved:
Male hypogonadism is a clinical and biochemical diagnosis. It should be diagnosed only when compatible symptoms or signs are accompanied by unequivocally and consistently low testosterone concentrations.
A total testosterone concentration below approximately 300 ng/dL, equivalent to about 10.4 nmol/L, is commonly used by the American Urological Association as a practical threshold supporting the diagnosis. This value should not be interpreted as an absolute stand-alone criterion because laboratory reference ranges, age, SHBG concentrations and the clinical presentation must also be considered.
Recommended diagnostic approach
In primary testicular failure, low testosterone is generally accompanied by elevated LH and possibly elevated FSH. In secondary or hypogonadotropic hypogonadism, LH and FSH are low or inappropriately normal despite reduced testosterone concentrations. A gonadotropin value within the laboratory reference range may therefore still be abnormal in the context of testosterone deficiency.
Weight reduction and management of contributing factors
For men with obesity-related functional hypogonadism, treatment of obesity and associated conditions is fundamental. Clinically meaningful weight loss may increase endogenous testosterone concentrations and improve metabolic health.
Management may include:
Because obesity-related reductions in testosterone may be reversible, lifestyle and weight-management treatment should generally be prioritised rather than assuming that every man with obesity and a low testosterone result requires testosterone therapy.
Testosterone-replacement therapy
Testosterone-replacement therapy may be considered when:
Available preparations include intramuscular testosterone esters, long-acting testosterone undecanoate and transdermal testosterone gels. Product selection and dosing should be individualised according to national approval, availability, patient preference, cost, pharmacokinetic profile and monitoring requirements.
Testosterone treatment may improve sexual symptoms, lean body mass, muscle strength, anaemia and bone mineral density in appropriately selected hypogonadal men. It may reduce fat mass modestly, but it should not be presented as a primary weight-loss treatment.
Fertility considerations
Exogenous testosterone suppresses LH and FSH secretion and can markedly reduce or completely suppress spermatogenesis. It is therefore generally unsuitable for men who are currently attempting to conceive or who wish to preserve fertility in the near future.
Men with secondary hypogonadism who desire fertility should be referred to an endocrinologist, urologist or reproductive-medicine specialist. Depending on the cause, alternative treatments such as gonadotropin therapy or selected oestrogen-receptor-modulating approaches may be considered under specialist supervision.
Contraindications and Precautions
Testosterone therapy should not be initiated without specialist assessment in men with conditions such as:
The precise contraindications and precautions may vary between guidelines and national prescribing information.
Monitoring During Testosterone Therapy
Clinical and laboratory monitoring is required after treatment begins. Follow-up generally includes:
An excessive rise in haematocrit requires prompt reassessment because testosterone therapy can cause erythrocytosis. The preparation may need to be reduced, paused or changed, and other contributing factors should be investigated.
Key Clinical Points
Obesity-related secondary hypogonadism is often functional and potentially reversible. A single testosterone measurement is not sufficient for diagnosis. Symptoms must be combined with consistently low morning testosterone concentrations, and free testosterone may be especially useful when SHBG is reduced.
Normal-range LH values do not exclude secondary hypogonadism. When testosterone is low, LH should normally increase; a low or normal LH concentration may therefore be physiologically inappropriate.
Weight loss and treatment of obesity-related comorbidities are central components of management. Testosterone therapy should be reserved for carefully selected symptomatic men with confirmed biochemical deficiency. It requires structured safety monitoring and should not be used in men seeking fertility.