Weight Loss and Male Fertility

Improving weight and metabolic health can support reproductive health. If you are trying for a baby, fertility assessment can happen alongside weight management, so you can act on both without waiting for a target weight.

Heracles brings weight care together with men’s health expertise. Our founders, Professor Suks Minhas and Professor Tet Yap, are consultant urologists and andrologists. Meet the team behind your care.

At a glance

• Weight is one part of fertility; semen results and both partners’ circumstances also matter.
• Weight loss may improve reproductive measures, but does not guarantee pregnancy.
• Discuss fertility plans before hormone treatment: external testosterone can suppress sperm production.

How can obesity affect male fertility?

Male fertility depends on sperm production and transport, sexual function, hormones, genetics and the health of both partners. Obesity can intersect with several of these systems.

Possible pathways include:

• altered signalling between the hypothalamus, pituitary gland and testes;
• lower sex hormone-binding globulin and, in some men, lower testosterone;
• insulin resistance, inflammation and oxidative stress;
• higher scrotal temperature;
• sleep apnoea and poorer general health;
• erectile or ejaculatory difficulty;
• medicines and conditions associated with obesity.

These are biologically plausible and supported to different degrees, but they do not prove why a particular couple is having difficulty. A man with obesity can have normal semen results, while a man with a lower BMI can have a significant male-factor problem.

NICE's 2026 fertility guideline advises that men with a BMI of 30 or above have an increased risk of reduced fertility. NICE: Factors that can affect fertility

Does obesity always mean poor sperm quality?

No. Population studies show associations, not a diagnosis for an individual.

Semen analysis measures characteristics such as volume, sperm concentration, total count, motility and morphology. These values naturally vary between samples and do not measure every aspect of sperm function. They also cannot predict pregnancy with certainty.

The European Association of Urology notes that obesity is associated with reduced sperm quality and lower testosterone, but also that evidence on the effect of weight loss on semen parameters is limited, non-controlled and conflicting. EAU male-infertility guideline

Assessment should identify the modifiable risks and clinical causes present now. Body weight alone cannot determine whether a man is infertile.

Can weight loss improve sperm health?

It may improve some reproductive measures in some men, but the evidence is not strong enough for a guarantee.

Weight reduction can improve insulin resistance, sleep apnoea, blood pressure, mobility, sexual function and obesity-related suppression of testosterone. Each of those changes can support reproductive health. Small studies have reported improvements in sperm concentration or count after lifestyle-induced weight loss, but study designs, participants and outcomes differ.

The EAU concludes that lifestyle improvement may help sperm quality and chances of conception, while specifically cautioning that weight-loss evidence is conflicting. It also reports that a meta-analysis of bariatric-surgery studies did not demonstrate improved sperm quality. EAU male-infertility guideline

Better metabolic health remains a valid objective even when semen changes are uncertain. Bariatric surgery may be the right obesity treatment for an eligible patient, but it should not be presented as a fertility intervention.

Do not delay fertility assessment while losing weight

Sperm production takes roughly three months, so changes in semen cannot be assessed meaningfully from one week to the next. At the same time, fertility is a couple-level and time-sensitive issue.

Investigation should not stop while a man works on weight. Parallel care can include:

• reproductive and sexual history;
• semen analysis performed to an appropriate laboratory standard;
• examination when indicated;
• hormone testing based on symptoms and semen results;
• review of medicines, testosterone and anabolic-steroid exposure;
• assessment of metabolic health and sleep apnoea;
• evaluation of the female partner or other partner-specific factors through the appropriate service;
• early specialist referral when results or history warrant it.

NICE recommends repeating an abnormal semen test, ideally around three months later, while allowing an earlier repeat when azoospermia or severe oligozoospermia is found. After two or more abnormal tests, men should be offered examination and considered for relevant hormone testing. NICE NG257 fertility guideline

Testosterone, anabolic steroids and sperm production

External testosterone can make a blood testosterone result rise while sperm production falls.

Testosterone therapy and anabolic-androgenic steroids suppress luteinising hormone and follicle-stimulating hormone, reducing the signals needed for the testes to produce sperm. The effect can be severe, and recovery after stopping is variable in timing and completeness.

NICE advises clinicians to ask men and trans women with fertility concerns about testosterone replacement therapy and other medicines that may affect fertility. NICE also advises not to offer androgens to men with semen abnormalities because they do not improve fertility. NICE male-factor fertility management

Men who want children now or in future should discuss that objective before starting testosterone. A low testosterone result in this setting requires a fertility-aware endocrine or andrology pathway, not automatic replacement.

Non-prescribed anabolic steroids deserve the same open, non-judgemental discussion. The clinician needs to know what was taken, at what dose and when, because this changes the investigation and recovery plan.

What about GLP-1 and GIP/GLP-1 weight-management medicines?

Direct evidence on current weight-management medicines and male fertility is still limited. Improvements in weight and metabolic health may be beneficial, but that is not the same as demonstrating that a medicine improves sperm or pregnancy outcomes.

NICE advises asking people with fertility concerns about GLP-1 receptor agonists and other medicines and discussing their possible effects on fertility. NICE: Factors that can affect fertility

A man planning conception should tell both the fertility clinician and the medicine prescriber. He should not stop, switch or alter a prescribed weight-management medicine without advice. The decision should consider the indication, treatment benefit, current evidence, other health conditions and the couple's timeline.

Online claims that semaglutide or tirzepatide "boosts male fertility" go beyond the evidence. Where studies report hormone or sperm changes, they are often small and cannot establish the chance of conception or a live birth.

Other medicines and exposures to review

The fertility history should include prescription, non-prescription and recreational substances. Relevant examples may include:

• testosterone and anabolic steroids;
• finasteride or dutasteride;
• opioids;
• some psychotropic medicines;
• chemotherapy or radiotherapy exposure;
• cannabis and other recreational drugs;
• supplements or products bought online.

This list does not mean every medicine causes infertility or needs to be stopped. Stopping essential treatment can be harmful. The purpose is to identify timing, dose and plausible effects, then make a supervised decision.

NICE specifically recommends asking about GLP-1 agonists, testosterone replacement, finasteride, over-the-counter medicines and recreational drugs when fertility is a concern. NICE: Factors that can affect fertility

Which lifestyle changes are worth making?

A useful preconception plan focuses on health changes with wider benefits rather than an unproven fertility "detox".

Consider:

• a sustainable, nutritionally adequate weight-management plan;
• regular physical activity and resistance training appropriate to ability;
• stopping smoking;
• keeping alcohol within UK low-risk guidance and avoiding heavy intake;
• treating diabetes, high blood pressure and sleep apnoea;
• improving sleep and recovery;
• avoiding non-prescribed anabolic steroids and recreational drugs;
• preventing excessive heat exposure to the testes where practical;
• reviewing occupational or environmental exposures when relevant.

NICE notes that smoking is associated with reduced semen quality and that excessive alcohol is detrimental to semen quality. It also states that the effectiveness of complementary therapies for fertility has not been properly evaluated. NICE: Factors that can affect fertility

No supplement should be presented as a substitute for diagnosis. "Male fertility" products may contain overlapping nutrients, undeclared ingredients or doses that are unnecessary, and evidence for improving live-birth outcomes is limited.

When should a man seek assessment?

Arrange fertility assessment according to the couple's circumstances, not only the man's age or weight. Earlier assessment is appropriate when there is:

• a history of undescended testes, testicular injury, torsion or cancer treatment;
• previous groin, pelvic or reproductive surgery;
• very small testes, a scrotal mass or persistent pain;
• erectile or ejaculatory difficulty;
• prior testosterone or anabolic-steroid use;
• known genetic or endocrine disease;
• a previous abnormal semen test;
• concern about the female partner's age or reproductive health;
• any reason the couple's time to treatment may be limited.

The NHS advises speaking to a GP when pregnancy has not occurred after a year of regular unprotected sex, with earlier review in relevant circumstances. NHS: Low sperm count

Bring your fertility plans into the conversation

Tell the Heracles team about your conception plans, any semen results and current medicines when discussing weight care. This helps identify where fertility or hormone assessment is relevant while you work on metabolic health.

Explore Heracles weight-loss care. Arrange fertility assessment alongside it when conception is a current priority.

More frequently asked questions

Should I take fertility supplements?

Evidence for improving pregnancy or live-birth outcomes is limited. Review supplements with a clinician and do not let them delay investigation.

Can bariatric surgery improve male fertility?

Bariatric surgery can improve obesity-related health, but current evidence does not reliably show improved sperm quality. Fertility timing and nutritional monitoring should be discussed with the bariatric and fertility teams.

Start with a weight-care assessment that includes your wider health priorities. Start your Heracles assessment.