Obesity has been a human health issue for centuries. Historically, it was viewed as a symbol of prosperity, wealth, and high social status. However, as civilization has progressed, obesity has become increasingly visible and dangerous, now considered an epidemic of the 20th and 21st centuries and classified as a “disease of civilization.” The body mass index (BMI), calculated as weight in kilograms divided by height in meters squared (kg/m²), is commonly used to assess body weight status. According to World Health Organization (WHO) guidelines for adults, BMI values are classified as follows: 25.0–29.99 for overweight, 30.0–34.99 for first-degree obesity, 35.0–39.99 for second-degree obesity, and above 40.0 for third-degree (so-called morbid obesity) [1, 2].
The primary cause of obesity is excessive caloric intake, but genetics also play a role, with around 40% of body fat variability attributed to genetic factors. Obesity contributes to approximately 7.1% of deaths globally, is a cause of disability in 1 in 20 patients, and is associated with a range of health complications over 200 have been identified so far. The most common complications include metabolic disorders such as type 2 diabetes, insulin resistance, and lipid imbalances, as well as hypertension, ischemic heart disease, obstructive sleep apnoea, osteoarthritis, depression, and an increased risk of various cancers [3–5]. Data from Poland after 2020 indicate that more than 65% of Poles are overweight or obese, with men comprising a majority of this group. Obesity affects 15.4% of men and 15.2% of women, with 0.5% of men and 0.4% of women classified as morbidly obese (BMI ≥ 40 kg/m²) [6, 7]. It is estimated that around 5 million people in Poland suffer from obesity, including nearly 1.5 million with second-degree obesity and approximately 290,000 with third-degree (morbid obesity) [8]. According to estimates from the Supreme Audit Office (NIK) in 2022, over 9 million adults in Poland were affected by obesity, with direct healthcare costs for the condition reaching PLN 9 billion [9].
Clinical effects of obesity on infertility in women
Obesity negatively impacts women’s reproductive potential, primarily through functional changes in the hypothalamic-pituitary-ovarian (HPO) axis. Obese women often exhibit elevated blood insulin levels, which stimulate the production of ovarian androgens. These androgens, converted into oestrogen through excess adipose tissue, create a negative feedback loop on the HPO axis, disrupting gonadotropin production. This disruption leads to menstrual irregularities and ovulatory dysfunction. Hyperinsulinemia plays a key role in the pathogenesis of polycystic ovary syndrome (PCOS), which is characterized by oligomenorrhea and hyperandrogenism. Obesity stimulates insulin resistance and appears to worsen PCOS symptoms, with more severe cases frequently observed in obese women. Elevated androgen levels in PCOS contribute to visceral fat accumulation, furthering insulin resistance and hyperinsulinemia, which in turn stimulate additional production of ovarian and adrenal androgens creating a self-reinforcing cycle. The prevalence of PCOS among obese women may be as high as 30%, although a direct causal link between obesity and the development of PCOS has not been established. Obesity has also been associated with a longer time to conception. Two large cohort studies of Danish women attempting to conceive showed a decrease in fertility rates as body mass index (BMI) increased. Notably, obesity may reduce fertility even in the absence of ovulatory dysfunction. A study of over 7,000 U.S. women found reduced fertility among obese women with regular menstrual cycles, and data from a cohort of over 3,000 Dutch women with regular cycles indicated that the likelihood of spontaneous conception decreased with increasing BMI above 29 kg/m². Obesity also affects the outcomes of assisted reproductive technology (ART), suggesting that its impact on fertility extends beyond ovulatory issues. Obese women undergoing in vitro fertilization (IVF) tend to have smaller oocytes with lower fertilization success rates. Numerous studies have demonstrated a negative effect of obesity on live birth rates (LBR), with an inverse correlation between LBR and BMI. A review of ART outcomes in overweight and obese women found a slight reduction in LBR, with an average odds ratio of 0.90. However, a large study of women with class III obesity (BMI > 40 kg/m²) observed a 50% reduction in live birth chances [10–19].
Clinical effects of obesity on infertility in men
Obesity in men significantly impacts fertility, as demonstrated by numerous clinical and epidemiological studies. Men with excess body weight often have poorer semen parameters, including lower sperm concentration, reduced motility, and abnormal morphology. Adipose tissue produces reactive oxygen species that can damage sperm DNA, diminishing their fertilizing potential. Additionally, obesity disrupts the hormonal system-excess adipose tissue promotes oestrogen production via aromatization of androgens, while reducing testosterone levels. This imbalance leads to hypogonadism, which in turn results in poor semen quality and reduced libido. Increased body weight is also linked to higher scrotal temperatures, which can negatively impact spermatogenesis, as the testes are sensitive to even slight temperature increases. Furthermore, insulin resistance and elevated leptin levels, commonly observed in obese men, may disrupt the hormonal function of the hypothalamic–pituitary–gonadal axis, resulting in decreased testosterone production and impaired spermatogenesis. Research suggests that weight loss, a balanced diet, and regular physical activity can improve fertility in obese men. Studies of patients following bariatric surgery have shown improvements in testosterone levels and semen parameters in some cases, indicating that weight loss may benefit reproductive health. The complex effects of obesity on male fertility highlight the need for further research into effective strategies to enhance reproductive capacity in overweight men [20–23].
Reproductive health and bariatric obesity treatment
According to the WHO, sexual health is an essential component of overall human health. The WHO defines sexual health as “the integration of biological, emotional, intellectual, and social aspects of sexual life necessary for the positive development of personality, communication, and love” [24]. Sexual dysfunctions are common among individuals with overweight and obesity, with studies indicating significantly poorer sexual functioning compared to individuals with normal weight. This includes reduced libido, painful intercourse in women, and erectile and ejaculatory disorders in men. Sexual dysfunction often accompanies obesity-related conditions: hypertension is frequently associated with lowered libido and erectile and ejaculatory issues, while diabetes can lead to painful intercourse, vaginal dryness, and decreased libido. Additionally, excess weight reduces physical fitness and endurance, leading to rapid fatigue, which further contributes to reduced libido and satisfaction with sexual activity [22–25].
In the context of the global obesity epidemic, bariatric surgery has gained recognition as the only treatment method that offers sustainable weight loss while improving metabolic health and overall quality of life. Bariatric surgery is a medical specialty focused on treating severe obesity and includes comprehensive interventions, such as conservative therapy (developing personalized dietary plans, teaching proper nutrition, and self-monitoring), non-surgical methods (e.g., gastric balloon implantation), as well as plastic surgery and gastrointestinal surgery [8].
The KOS-BAR program was established in response to the growing challenge of morbid obesity, which presents significant medical and socioeconomic issues. In Poland, the program was introduced by the Regulation of the Minister of Health on August 12, 2021, establishing a pilot initiative for comprehensive specialist care for patients with morbid obesity, known as KOS-BAR (Journal of Laws 2021, item 1622). The program provides coordinated, comprehensive care before and after surgery at designated centres. It is available to patients aged 18 and older with an ICD-10 diagnosis of E66, indicating obesity due to excessive caloric intake. To join, patients must register a referral to the General Surgery Clinic with this diagnosis. Eligibility is determined by a bariatric surgeon based on the following criteria: (1) a body mass index (BMI) of ≥ 40 kg/m², or (2) a BMI of 35–40 kg/m² in patients for whom weight loss could improve obesity-related conditions such as type 2 diabetes, hypertension, cardiovascular diseases, sleep apnoea, joint diseases requiring surgery, non-alcoholic steatohepatitis, hyperlipidaemia, or female infertility, including infertility related to polycystic ovary syndrome [26].
Summary
Clinical studies clearly show that obesity increases the risk of subfertility, affecting not only natural fertility but also responses to assisted reproductive technologies (ART). Prevention and treatment of obesity are therefore essential components of reproductive health care and play a crucial role in developing therapeutic strategies for individuals facing fertility challenges. A comprehensive approach including lifestyle modifications, psychological support, and, when appropriate, surgical interventions such as bariatric surgery can significantly improve reproductive health outcomes in patients with obesity.
Article information and declarations
Author contributions
K. Zborowska — review of the literature on the impact of obesity on reproductive health and text editing; D. Jorg — review of the literature on obesity and the KOS-BAR program; Lukasz Wicherek — manuscript, substantive evaluation
Conflict of interest
All authors declare no conflict of interest.
