The fact that weight gain affects fertility has long been established. However, the mechanism behind it continues to be studied, and the one common denominator that emerges from these studies is hormone imbalance. Repeatedly, science shows that obesity- defined by having a BMI measurement of 30 or above - disrupts normal hormonal balance, which directly influences a woman’s reproductive cycle and thus, her ability to conceive. And while one may think that only the reproductive hormones are involved, a variety of other hormones actually play key roles in regulating fertility.
Tipping the hormonal scales Excess fat influences the production of a gonadotropin-releasing hormone (GnRH), a hormone that triggers the release of two other hormones essential for proper development of eggs: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). GnRH is also important for maintaining regular ovulation. When levels of any or a combination of these hormones are either too high or too low, fertility can be impacted negatively.
Furthermore, excess fat can create an estrogen imbalance. An overly-abundant supply of estrogen disrupts the normal function of ovaries, which can then affect the cycle and subsequently, lead to infertility.
The most commonly associated link between fertility and obesity is that of insulin resistance. High levels of the hormone insulin in the blood is a common feature of obesity, type 2 diabetes, metabolic syndrome, and polycystic ovarian syndrome (PCOS), which is the most common cause of infertility among women. A number of studies have shown that women with insulin resistance typically have decreased rates of fertility, with most scientists theorizing that because the cells have become resistant to insulin, they then became “deaf” to signals that would tell the body to produce the hormones needed to maintain proper ovarian function, leading to infertility. This is why it became common practice to address insulin resistance before any other issue, with some fertility clinics even refusing to accept obese patients until they have lost some weight.
However, a study in 2010 has challenged this widespread belief, instead suggesting that while it’s still an important issue that needs to be addressed, insulin resistance alone is not the main culprit. Researchers in John Hopkins Children’s Center, led by Andrew Wolfe, Ph.D. have discovered that the pituitary gland- often dubbed the “master gland” of the body because it controls other glands and regulates the release and secretion of hormones critical for everyday function- played a major role in the mechanism that connected insulin resistance to infertility.