Does Obesity Affect Fertility?

Obesity is a chronic disease that is defined as a body mass index (BMI) of greater than 30 kg/m² and is one of the leading causes of death and illnesses worldwide.^1,2 In addition to its detrimental effects on metabolic health, studies have consistently shown that obesity adversely impacts reproductive health in both women and men.³ 

Increased risk of infertility is also one of the many consequences of obesity.⁴ Infertility is defined as a lack of pregnancy despite >1 year of unprotected sexual intercourse and is shown to be much more prevalent in individuals who are obese. Research shows that obese women have a threefold higher risk of infertility than nonobese women, with some studies finding the risk of infertility to be nearly 80% in women who are obese.⁵ Additionally, the probability of pregnancy is shown to decrease by 5% per unit of BMI over 29 kg/m².

How Does Obesity Affect Fertility in Women?  

Obesity affects various aspects of reproductive health in women, including anovulation (ie, absence of ovulation), menstrual disorders, miscarriage, infertility, challenges to assisted reproduction, and negative pregnancy outcomes.³

It is important to highlight the role of adipose (ie, fat) tissue in the body in order to understand its effect on fertility.⁴ Adipose tissue is not mere storage for fat, but is an endocrine organ that actively secretes hormones affecting physiological functions, including reproduction. Recent years of research have discovered that immune-related proteins (ie, cytokines) specifically released by adipose tissues – known as adipokines – are vital to female reproduction. High levels of adipose tissue can impair hormonal balance, releasing abnormal levels of certain adipokines that can disrupt the hypothalamus-pituitary-gonadal axis that regulates female reproductive functions. Such disruptions are also known to be associated with insulin resistance, type 2 diabetes mellitus, and inflammation. Through complex mechanisms, hormonal dysregulation and insulin resistance can impair secretion of hormones critical to female fertility.

How Does Obesity Affect Fertility in Men?

Although not as well studied or understood as obesity’s effect on female fertility, male fertility is also known to be greatly affected by obesity.^5,6 Male obesity is thought to affect male fertility primarily by disrupting sperm quality and quantity, with studies showing that obesity in men is associated with low or no sperm count and greater risk of abnormal sperm formation. More research is needed, but experts believe that the hormonal effects of adipose tissues play a significant role. Disrupted hormonal balances and insulin resistance caused by increased adiposity are thought to reduce levels of testosterone and increase levels of female hormones that impair production of sperms. In addition to disrupting hormones, adipokines released by increased adipose tissues can induce inflammation and oxidative stress in reproductive organs. Additionally, obesity is thought to increase testicular heat and risk of erectile dysfunction and is known to be associated with various metabolic disorders that are linked to male subfertility.

Weight Loss May be Key

It should be noted that a wide array of factors unrelated to obesity can influence fertility. Therefore, professional guidance should be sought to identify if other underlying issues exists. However, given the key role increased adipose tissue plays in disrupting hormonal balance in the body, weight loss in obese individuals can be impactful for fertility.^5–7 Decreasing adiposity can help restore balance in the hypothalamus-pituitary-gonadal axis and improve ovulation, insulin sensitivity, and receptivity in the uterus. Small studies in men have also shown that weight loss programs helped improve semen parameters. Reducing body weight by 5-10% is recommended, with the goal of reaching and maintaining a healthy BMI range of less than 25 kg/m². Lifestyle changes involving healthier diet and increased physical activity are recommended. Weight loss medications as well as bariatric surgery can be considered in certain individuals and have shown promising results in improving ovulation, normalizing menstrual cycles, fertility, as well as in improving other metabolic parameters such as cardiovascular risk in women.