While much has been said and written about the “obesity epidemic,” there is little discussion about what obesity really means and how it can affect health — including fertility. There is a growing and profound global impact of obesity on health, and understanding how these things are connected can help empower individuals to make informed decisions.
Obesity can negatively impact both male and female fertility and reproduction. For individuals assigned female at birth, obesity can result in a number of reproductive consequences that affect a variety of different steps in the reproductive process including ovarian follicular recruitment, egg development and quality, egg fertilization, and embryo development and implantation. For individuals assigned male at birth, obesity can impact fertility through various mechanisms, including hormonal imbalances, reduced sperm production, and lower sperm quality.
How is obesity defined?
Defined by the World Health Organization (WHO) as having an “abnormal or excessive fat accumulation that presents a risk to health,” obesity is a term that applies to individuals with a body mass index (BMI) over 30.
It is essential to know that obesity is not a moral failing or an indication of worth, lack of willpower, or inability to self-regulate. Obesity is a complex multifactorial disease influenced by a person’s genetics, environment, and psycho-social factors. While a subgroup of those with obesity may be obese due to a single factor like certain medications, diseases, immobilization, or more, most people with obesity are dealing with a variety of factors, including structural factors limiting the availability of healthy, sustainable, and affordable food, a lack of safe and accessible spaces for physical activity, and a lack of an effective and early health system response to weight gain.
What is the link between obesity and fertility?
There are several ways obesity can impact fertility for both men and women. To understand how obesity may affect reproduction, it’s important to know how adipose tissue (aka body fat) plays a crucial role in hormonal health and biological functions. In addition to cushioning soft organs, regulating hunger and satiety, providing insulation from cold and heat, and more, adipose tissue is composed of cells called adipocytes that store energy as fat. Because the body’s ability to reproduce is closely tied to the amount of energy reserves it has, too little or too much body fat can directly impact reproductive functions and disrupt the balance of certain hormones. Because of this delicate relationship between body fat and reproductive functions, obesity can affect a number of hormones, including estrogen, androgens, leptin, and adiponectin.
Excess adipose tissue is also associated with a disruption of the hypothalamic-pituitary-gonadal (HPG) axis. Made up of the hypothalamus, pituitary gland, and ovaries/testes, the HPG axis is crucial to reproduction. Obesity may disrupt the production of hormones from the hypothalamus that subsequently affects normal follicle development, ovulation, and sperm production. Additionally, obesity has been associated with a decline in egg quality and sperm counts.
Obesity can also have a negative impact on assisted reproductive technology (ART) outcomes. Obese individuals may require higher doses of medication and have more canceled cycles of in vitro fertilization (IVF), as well as lower embryo quality.
How obesity affects female fertility
Obesity can affect female fertility specifically in a number of ways:
Disrupted hormonal balance and ovulation cycles
In obese individuals, adipose tissue becomes the primary source of estrogen, and can often lead to elevated levels of the hormone. In women, this elevation can lead to irregular menstrual cycles, anovulation (lack of ovulation), and reduced fertility.
Insulin resistance
Obesity is often related to insulin resistance, and in women, elevated insulin levels may stimulate the ovaries to produce excess androgens, the steroid hormones mainly associated with male traits and reproductive functions. Excessive androgens are a known contributing factor to conditions like polycystic ovary syndrome (PCOS), also characterized by irregular periods and anovulation.
Chronic inflammation and uterine receptivity
Obesity is considered a state of chronic low-grade inflammation and also leads to heightened oxidative stress, which is an imbalance of free radicals and antioxidants, resulting in cellular damage. These characteristics contribute to metabolic disruptions and tissue damage, affecting various parts of the body, including the uterus. These changes in the uterus may make it difficult for an embryo to implant and develop into a pregnancy.
Increased risk of miscarriage and poor ART outcomes
Obese women have been shown to have lower implantation rates and higher miscarriage rates than non-obese women. Additionally, research has shown that the live birth rate among obese women is lower compared to non-obese women following assisted reproductive technology (ART) treatment, although the specific stages that obesity influences in this process are still unclear.
How obesity affects male fertility
Obesity can affect male fertility in a variety of ways as well, including:
Hormonal disruptions
The increased estrogen that results from obesity can result in infertility and erectile dysfunction. Excess adipose tissue increases the activity of an enzyme called aromatase, which converts androgens like testosterone to estrogen. This increased activity contributes to decreased testosterone in men, which can negatively affect sperm production.
Poor semen parameters
Obesity in men may result in reduced sperm count, motility, and morphology. Obesity has been associated with a significantly higher risk of having a low sperm count and studies have shown that as BMI increases, sperm concentration and total sperm count decrease. Obesity in men has also been associated with reduced sperm motility (asthenozoospermia), poor motility linked to mitochondrial dysfunction, and abnormal sperm morphology, i.e. the size, shape, and structure of the sperm.
Increased oxidative stress and DNA fragmentation in sperm
Obesity in men is also linked with increased oxidative stress. This oxidative stress has been shown to significantly impair sperm quality (including count, motility, morphology, and DNA integrity), which can result in male infertility. Oxidative stress is also associated with sperm DNA fragmentation, meaning breakage or damage to the DNA within sperm cells, which can negatively affect fertilization and pregnancy outcomes.
Elevated scrotal temperature affecting sperm production
Increased adipose tissue has been associated with changes to testicular temperature, which can negatively impact sperm production and quality.
Higher rates of erectile dysfunction and decreased libido
Through vascular damage, hormonal imbalances, chronic low-grade inflammation and more, obesity is associated with erectile dysfunction and decreased libido, impacting reproduction and fertility. Research has shown that a reduced libido is also a common cause of sexual dysfunction among obese men.
Weight loss benefits
Weight loss has shown to offer significant benefits for fertility in obese men by addressing many of the underlying issues that affect sperm production and quality, hormone levels, and fertility outcomes.
The importance of lifestyle factors in managing obesity
For men and women, lifestyle factors can play an essential role in the relationship between obesity and fertility. While genetics and certain medical conditions can contribute to obesity, maintaining health-promoting lifestyle behaviors can make a significantly positive effect on reproductive health.
Diet
Nutrition plays an integral role in managing obesity, and in addition to the quantity of calories a person consumes, experts believe the quality of food matters to overall health as well. While calories in/calories out is an important concept to consider, there are many more factors at play when it comes to managing obesity, including living in an environment that lacks access to healthy food options and navigating income-related barriers to healthy food. Additionally, the prevalence of low-nutrient ultra-processed foods and beverages high in sugar may negatively affect a person’s diet, as well as unhealthy eating behaviors including restriction and overeating.
According to the WHO, a healthy diet consists of a combination of different foods including cereals, legumes, fruits, vegetables, and foods from animal sources. While every person’s diet may be unique, an important principle of a healthy diet is to limit energy intake from total fats and sugars and increase intake of these healthy staples.
Many of the nutritional principles related to obesity also benefit fertility. For example, consumption of sugary beverages like sodas and energy drinks has been linked to lower fertility for men and women, so avoiding these options is recommended. In addition to these core principles, research has found that couples who ate more seafood were able to get pregnant sooner than those who rarely ate seafood. Experts have also found folic acid, vitamin B12, omega-3 fatty acids, and generally healthy eating plans like the Mediterranean diet to have a positive impact on fertility in women.
Exercise
In addition to contributing to a calorie deficit, which is considered fundamental for weight loss, consistent exercise is considered essential for maintaining long-term weight loss and preserving muscle mass. Exercise has also been associated with the prevention of obesity-related illnesses, including several types of cancer. While excessive exercise has been associated with negative influences on fertility, researchers believe physical activity and decreased sedentary behavior may improve fertility through the maintenance of a healthy body weight and hormonal levels.
Sleep
Sleep plays an integral role in metabolic function, hormonal balance, and appetite control, which all contribute to obesity. Low quantity and quality of sleep can directly contribute to obesity and make weight loss more challenging by disrupting hormones like leptin and ghrelin, which help regulate appetite, and cortisol, otherwise known as the stress hormone. Poor sleep can also lead to insulin resistance and reduced glucose tolerance, which can both contribute to weight gain. Sleep deprivation has also been shown to disrupt the metabolism by altering circadian rhythms and increasing systemic inflammation. Research has shown better subjective sleep quality, as well as sleeping more than 7 hours per night increased the chances of successful weight loss by 33%.
Stress
Stress can influence the development of obesity through a variety of mechanisms including hormonal responses, behavioral changes, physical activity levels, and more. Because it encourages the body to produce increased levels of cortisol, stress can result in increased appetite, visceral fat storage, and more. Stress is also a common cause of emotional eating and can contribute to poor food choices, reduced physical activity, and disrupted sleep. Learning techniques to manage stress — like mindfulness — can help foster a more positive relationship with food and exercise, and help manage some of the factors that contribute to obesity.
How weight loss can improve fertility
Research has shown that weight loss — even as modest as a 10-15% reduction in body weight — can have a significantly positive impact on fertility for both men and women who are obese. In obese women, weight loss can improve insulin sensitivity and restore balance in the HPG axis, leading to adequate levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are essential for egg development and ovulation. Weight loss can also improve uterine receptivity and lead to better success with ART through higher pregnancy and live birth rates, fewer complications, and an improved response to medications. For men, weight loss can result in reduced aromatase activity and estrogen, which helps increase testosterone levels, enhanced sperm parameters like concentration and motility, improved sexual function, and more.
As a result of these comprehensive findings, Carrot has introduced Sprints, the first-and-only program to address infertility linked to obesity and poor metabolic health. With a focus on hyperpersonalized habit-building, Sprints empowers members to optimize their nutrition, movement, sleep, and stress management in order to improve the chances of getting pregnant faster — ideally without the need for expensive interventions.
Because metabolic dysfunction is the fastest growing cause of infertility and high-risk pregnancies, Carrot has launched Sprints to target the root causes of metabolic-related infertility and provide dynamic programs tailored to each individual. Led by a team of world-class doctors, Sprints is designed to enhance metabolic health in the pre-pregnancy stage, reducing costs, and increasing the odds of a healthy pregnancy for each member.
GLP-1s and their role in obesity-related infertility
GLP-1 receptor agonists (often referred to as GLP-1s) are a class of medications that mimic the action of a natural hormone in the body called glucagon-like peptide-1 (GLP-1). While GLP-1s are most commonly prescribed as a treatment for type 2 diabetes, they are increasingly being prescribed for weight loss and as a treatment for obesity. While GLP-1s primarily support weight loss by acting on the brain as appetite suppressants that promote satiety, they also slow gastric emptying, helping users feel full for longer periods of time, and may help improve metabolic health in other ways.
GLP-1 medications are not appropriate for every person, but for some people with obesity and/or PCOS, they can help aid weight loss, which in turn, may help improve fertility. While not recommended for women who are pregnant or actively trying to become pregnant, evidence suggests that GLP-1 medications can improve ovulatory and metabolic function in obese women who may want to attempt pregnancy in the future. Because of these potential benefits, Carrot provides managed access to fertility-supporting medications including GLP-1s like semaglutide and tirzepatide through Sprints for members facing obesity-related fertility challenges.
Frequently asked questions (FAQ)
Can obesity alone prevent pregnancy?
While there are many potential causes of infertility, it is possible that obesity alone can negatively affect fertility and significantly reduce the chances of pregnancy and/or a healthy delivery.
Does male obesity affect fertility as much as female obesity?
Obesity in both males and females can significantly impact fertility through a variety of mechanisms. While female obesity may affect ovulation and the quality of eggs, male obesity can impact sexual function, the quantity and quality of sperm, and hormonal levels that are necessary for sperm production. All of these factors directly affect the ability to fertilize an egg and contribute to pregnancy.
How much weight loss is needed to improve fertility?
Every person is unique, and each person’s needs are distinct when it comes to fertility, which is why Sprints is a hyper-personalized approach to metabolic optimization. Evidence does suggest, however, that in many cases, even a modest weight loss of 5-10% of a person’s body weight may significantly improve fertility.
Are GLP-1 medications safe for fertility patients?
While GLP-1 medications are not appropriate for every person, they may be beneficial to some people facing obesity-related fertility challenges, especially those who have been diagnosed with PCOS. For these individuals, GLP-1s can be highly beneficial in the pre-pregnancy phase, but are not considered appropriate for people who are currently pregnant or actively trying to become pregnant.
How long should I maintain a healthy weight before trying to conceive?
Every person is unique in their metabolic and fertility needs, but experts generally recommend achieving and maintaining a sustainable weight loss until the body shows measurable signs of metabolic and hormonal improvement (like the resuming of regular menstrual cycles for women or improved sperm test results for men). While there is no universal recommendation for how long a person should maintain a healthy weight prior to pregnancy, adopting healthy food, exercise, and other lifestyle habits can continue to support overall wellness through pregnancy and beyond.
Obesity and fertility: A way forward
Obesity can significantly impact both male and female fertility through hormonal, metabolic, and physical mechanisms. Lifestyle change should be a cornerstone of fertility treatment for those with high BMI. GLP-1 medications may offer additional metabolic benefit for select patients but require careful reproductive planning. Individualized, medically supported care is key to optimizing fertility while managing weight.
