obesity and male fertility

There has been a huge rise in cases of obesity worldwide over recent decades. This, in turn, is leading to a health crisis with increases in rates of diabetes, heart disease and other long term health conditions. A shocking 68% of men in the UK are either obese or overweight.

Could there be a link between this rise in obesity levels and the decline in male fertility rates? Probably!

How is obesity defined?

Obesity is generally measured by the body mass index (BMI). This is calculated by dividing weight in kilograms by height in meters (squared)

Although this is not always the most truly accurate measure, it is generally accepted as the go to standard within the NHS. It is worth noting that someone’s BMI can easily be skewed if a person has a higher density of muscle mass or is particularly lean.  


The BMI ranges are as follows:




Under 18.5


18.5 – 24.9


25 – 29.9


30 – 39.9

Severely obese


Another measure that is sometimes used is body fat index or body fat percentage (BF). This is calculated using callipers to measure the thickness of the fat underneath the skin across 3 areas of the body. Having reviewed multiple research papers, we found that both BMI and BF were used as measures against fertility, although it seems there is a stronger correlation between BF and fertility rather than with BMI. Either way, if you are overweight or obese according to your BMI, then chances are you will also be high in BF and the research shows this will definitely impact your sperm health.

How does being overweight affect your fertility?

From the research we reviewed, the true mechanism of how high body fat impacts sperm health is yet to be fully understood. However, the evidence that it does impact sperm health seemed pretty indisputable.

Research shows that obesity has a significant impact on the Hypothalamic–pituitary–gonadal (HPG) axis i.e., how the brain, the pituitary and testicles interact. This finely balanced system relies on a complex series of hormones and messages being passed between them to keep our reproductive system in balance. Higher fat levels seem to create a significant imbalance in many of the hormones that play a key role in sperm production including testosterone, inhibin, and oestrogen. Body fat, especially abdominal fat, produces estrogen and leptin which act on the brain to secrete less gonadotrophin releasing hormone (GnRH) the main hormone that drives the release of follicle stimulating hormone and luteinising hormone which subsequently promote spermatogenesis. Consequently, the Leydig cells located in the testicles will be less stimulated to produce testosterone. Yet, less testosterone will, in turn, lead to the production of more fat which turns more testosterone into oestrogen. Higher oestrogen levels lead to further fat deposits creating a vicious circle of increased fat and increasing hormone imbalance. Hence, this is a vicious cycle.

Men with a higher level of fat in their system have lower testosterone levels, higher oestrogen levels and are more likely to have lower sperm counts and sperm concentration. Some research showed that motility and morphology were not as likely to be impacted, however there is more to consider than just the standard semen parameters.

Further impacts

In addition, too much abdominal fat also produces pro-inflammatory factors that also negatively act on the brain. Additionally, these factors are leading to increased inflammation in the body causing higher oxidative stress, which is also bad for sperm health and only adds to the already bad picture created by the hormone imbalance with further damage to the sperm occurring in the form of DNA fragmentation. Obese men are more likely to have raised oxidative stress and high sperm DNA fragmentation. This is why a standard semen analysis where sperm concentration, motility and the shape of the sperm are examined, may not be showing the true level of damage occurring.

Increased scrotal temperature is also a concern for those that are obese. Research has shown that obese men are less active and live a more sedentary lifestyle. Lack of movement combined with the potential of greater fat deposits in the lower abdomen and genital area all contribute to increases in scrotal temperatures. This raised heat stress damages sperm during the maturation process and its subsequent storage.

Part of the big problem we have in the western world is the increase in heavily processed foods with the use of poor-quality fats and sugars. These foods are well known to be inflammatory in nature whilst also contributing to insulin resistance and greater levels of body fat.

A further problem seen in obese men is obstructive sleep apnoea (OSA), a condition in which the walls of the throat relax and narrow during sleep causing breathing to be restricted or even stop temporarily. The result being that those with OSA often have poor or disturbed sleep leading to cardiovascular disease, insulin resistance and other hormone and metabolic conditions. Men with OSA are more likely to have raised levels of oxidative stress, increased sperm DNA fragmentation and poor sperm quality.

Just lose weight, right?

Seemingly from some of the research we reviewed, losing weight may not always make a difference. More research is needed to understand the effects of weight loss on improving sperm quality as varying results have been seen in the studies conducted so far. As obesity is such a complex issue, it is hard for researchers to isolate all the elements to establish exactly what part of being overweight is creating the issue and why. It’s also not clear why some men’s samples improve, and others do not. This raises the question of whether obesity creates a permanent change in hormone imbalances and spermatogenesis. Either way there are more than enough other health concerns from obesity that justify the need to lose weight no matter what. 

Positive steps to control your weight

Most people know instinctively what they need to do to live a healthier life, but that does not always mean it is easy. Obesity is a multi-faceted and sometimes complicated condition, and it is all too easy to assume someone is overweight just because they eat rubbish food. There can be all manner of things going on physiologically and emotionally that could be making it hard for them to manage their weight.   

Most of the advice for improving your lifestyle and diet also fits with improving sperm quality so whether you are attempting to lose weight or improve your sperm quality (or both) the advice is generally the same.

Top tips include:

  • Avoid processed foods which contain bad fats and sugars (this includes takeaways)
  • Eat a balanced healthy diet with plenty of fresh vegetables, fruit, oily fish and lean meat
  • Reduce or cut out sugary drinks including alcohol (it is loaded with sugar too)
  • Drink plenty of water
  • Move more and exercise regularly – make a plan and stick to it or consider getting a personal trainer
  • Create healthy habits – the best way to manage your weight and stay healthy is to actually change your lifestyle and stick to it rather than hit it with fad diets or crash dieting.

For even more tips on diet and lifestyle essentials check out this article from Melanie Brown.

If you are struggling to control your weight, then speak to your GP to find out what support might be available to you.

In summary

It is a well-known fact, and has been for some time, that obesity contributes to a myriad of health complications that could potentially be avoided. The research also seems pretty conclusive that obesity is not good for our sperm health. The level of hormone disruption and the damage that occurs seems to be considerable which should make managing your weight whilst trying to conceive a high priority (of course, for general health as well).

However, it is not always that easy. With life being busy and stressful and with the added pressures of fertility treatment or trying to conceive, it is all too easy to reach for the high fat and high sugar foods to get that dopamine hit in the hope that it will make you feel better. Making sure you are aware of how your food choices may be impacting your chances of trying to conceive might help you make better choices when things are not going to plan. However, if you are struggling, then it is important to reach out for support so that you can take control of your health and fertility.

Research reviewed

Mah PM, Wittert GA (2010); Obesity and testicular function. Mol Cell Endocrinol 316: 180–186

Kelly DM, Jones TH (2013); Testosterone: a metabolic hormone in health and disease. J Endocrinol 217: R25-45

Bhattacharya K et. al. (2020); Obesity, systemic inflammation and male infertility. Chem. Biol. Lett. 7(2): 92‐98