The links between obesity and infertility

The links between obesity and infertility

Throughout this article, we use the words ‘obese’ and ‘obesity’. We recognise that may be triggering as those words have become burdened with negative connotations and for many being labelled as ‘obese’ is a cause of shame. This is not our intent. We use ‘obesity’ to describe a complex chronic condition that is a driver of other diseases – in this case, infertility. In many countries, obesity is recognised as a disease in itself.


Not everyone who is obese will have fertility problems

First, we want to say that being very overweight or obese doesn’t mean you will have fertility issues. The interactions between obesity and infertility are complex and the information available can seem confusing and even conflicting.  If you have been ‘large’ all your life, come from a family of bigger-than-average people, eat healthily, and exercise then you probably don’t have to worry.  In fact, most of us can point to a friend or relative who would have a high BMI but who has had no problems conceiving. 
However, many other women (and men) who carry additional weight do have trouble conceiving.  Reproduction is intricately linked to energy balance via a number of hormones and cellular interactions, so getting that balance right can help with fertility. 

Obesity does not cause infertility – but often adds to the burden

It’s important to say that while studies show that obese women are nearly three times more likely to develop infertility1, correlation is not causality i.e. obesity does not cause infertility. Instead, being very overweight and having fertility issues are both outcomes of unbalanced hormones. So, when we talk about “obesity-related infertility” we mean exactly that – obesity and fertility are linked but obesity isn’t causing your infertility. 
We know that statistically, obese women are more likely to not ovulate, have irregular menstruation, elevated risk of miscarriages, have greater difficulties with IVF, and decreased live birth rates so understanding the root causes and dealing with those is crucially important. 

Relatively recent weight gain in adulthood can be a warning sign for future infertility

Those most at risk of obesity-related infertility tend to have been of regular weight when young and then had rapid weight gain after puberty or in early adult life. Obesity acquired in adulthood tends to be visceral fat (the fat that is around your middle and internal organs) which is more metabolically active, and which also induces inflammation in the body.

Adult weight (and the number of fat cells you have) in most situations is genetically determined. When we put on a large amount of weight, these fat cells enlarge in size.  The resulting stretch of the fat cells causes the release of a number of pro-inflammatory signals (called adipokines) which influence the metabolism and also interfere with ovarian and reproductive function.

Insulin resistance driven by this pro-inflammatory state adds to the mix. A number of studies have shown the association of this pro-inflammatory visceral fat with ovulation, embryo function, implantation, and overall pregnancy outcomes.

Fat cells produce many hormones that also can affect fertility

Adipose tissue (ie fat cells) produces many hormones including:

  • Leptin: Leptin has complex interactions with the reproductive function from stimulating puberty to suppressing estrogen in the sex organs, and influencing embryo implantation. Obesity is associated with high leptin levels which leads to a lack of sensitivity to the hormone – a condition known as leptin resistance.  This means that your body loses its ability to regulate correctly so that you are likely to eat more and exercise less than your body actually needs, and so leading to more weight gain.
  • Adiponectin is another hormone that the adipose (i.e. fat) tissue produces, which is known to have an impact on the regularity of ovulation and egg quality.
  • Pro-inflammatory cytokines: Stretched fat cells also produce pro-inflammatory cytokines which can have a negative impact on ovulation and menstrual regularity.
  • Sex hormone-binding globulin (SHBG): Visceral fat in the liver reduces sex hormone-binding globulin and increases the free androgen level which affects ovulatory function.  

Being very overweight increases the risk of developing polycystic ovarian syndrome (PCOS)

The ‘cysts’ in PCOS aren’t the cause of fertility issues, rather they are the result of a complex set of hormonal interactions gone awry that can cause infertility.  

PCOS is characterised by abnormal ovarian function due to insulin resistance and increased androgens (male hormones) in the blood.  Obesity increases the risk of PCOS as the fat cells expand and excrete hormones which leads to a hormonal imbalance that disrupts the normal functioning of the ovaries. 

These unbalanced hormones interfere with the development of ovarian follicles and timely ovulation causing delayed or irregular cycles, multiple ovarian cysts, and sometimes acne and unwanted facial and body hair growth. Additionally, women with PCOS have a higher risk of miscarriage and are more likely to develop gestational diabetes during pregnancy. 

Obesity can impact procedures

At Flinders Fertility, egg retrievals are carried out at the Glenelg Day Surgery. This is a low-risk surgical day facility, and has restrictions on BMI and weight to protect patient safety.  Complications with anaesthesia are much higher with obesity and anaesthetists require the full backup of a major hospital should the worst happen.  This is for your own safety.  While it pains us to have to do this, we would suggest that you choose a fertility clinic that uses Ashford Hospital or St Andrew’s Hospital for procedures. We can provide you with recommendations.

Obesity affects male fertility too

To be able to produce healthy sperm, the testes have to be cooler than normal body temperature at around 34-35C.  It is common for men with obesity to have an excess of abdominal, inner thigh, and pubic area fat which can increase the scrotal temperature and inhibit the production of sperm2.

Additionally, increased temperature leads to DNA fragmentation and increased oxidative stress which in turn changes semen parameters and function resulting in infertility.

How to reverse weight-related infertility 

Healthy Lifestyle
To improve fertility in patients with PCOS and obesity, we recommend a focus on creating a healthy environment for you and your future child.  The first 1000 days from pre-conception through to toddlerhood is where good nutrition can positively influence a baby’s lifelong health by reducing the risk of allergies, weight complications, and chronic diseases. 

Rather than counting calories and just focusing on weight loss, we recommend seeing a fertility dietitian who will take into account where you are now, your fertility goals and timing, and ensure that you are optimising your health. By shrinking the fat cells through exercise and a healthy, but not restrictive diet, you can reverse metabolic changes and restore the balance of hormones. 

Where diet and exercise alone aren’t working, treating the underlying metabolic conditions with medication can improve fertility.  The most common medications are Metformin, Semaglutide, Liraglutide, or a combination medication of Naltrexone and Bupropion called Contrave.

It is important to note that these medications are not proven to be safe for conception and therefore use when trying to conceive is not recommended. 

Seeking help

Reversing obesity is hard. Sometimes it feels like your body is working against you so rather than focusing on weight loss as an end in itself, we see more success in focusing on your overall wellbeing and that of your future child.

We recommend seeing a fertility dietitian for support. The Early Life Nutrition Alliance is a global group of fertility dietitians with a large member base in Australia.  They offer telehealth consultations and can give you the extra support you may need. Check out their website to book an appointment.

If you have been trying to get pregnant for over 12 months, (or have been diagnosed with PCOS), we recommend that you make an appointment with our endocrinologist  Associate Professor Vasant Shenoy.  We can investigate the underlying issues to regulate any hormone imbalance that could be causing your weight gain and affecting your infertility and then make an achievable plan to get back into balance.

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1. Adolescent body mass index and infertility caused by ovulatory disorders.
J W Rich-Edwards 1, M B Goldman, W C Willett, D J Hunter, M J Stampfer, G A Colditz, J E Manson in

2. Obesity, An Enemy of Male Fertility: A Mini Review.
Mohamed Ahmed Abd El Salam in Oman Medical Journal [2018], Vol. 33, No. 1: 3-6

Clinical Review by Associate Professor Vasant Shenoy