Weight can influence the amount of estrogen in your body.
Most people know that their ovaries produce estrogen, however, a lot of people don’t know that adipose tissue (fat cells) also produces some estrogen. When you’re at a healthy body weight, you have a higher probability of producing an appropriate amount of estrogen, but when you’re overweight or obese, your adipose tissue produces more estrogen than necessary—which can prevent regular ovulation. Without getting too in the weeds, your body requires a fine balance of hormones to ovulate properly, and having too much estrogen can throw off that balance.
On the flip side, when you’re underweight your ovaries make less estrogen, which can also impact ovulation (at ovulation, you need your estrogen levels to rise, helping along the release of the egg from its follicle). According to the Mayo Clinic, “being significantly underweight can affect hormone production and inhibit normal ovulation.” Plus, being underweight can stop menstruation altogether (what’s known as amenorrhea).
Obesity can impact male fertility, too.
If a doctor/friend/family member/anonymous internet commenter says that fertility problems are a woman’s issue, that’s simply not true. According to the CDC, in about 35 percent of couples, a male issue is identified along with a female issue. And in about 8 percent of cases, a specifically-male problem is identified as the sole reason for infertility.
In men, obesity is associated with lower testosterone and impaired sperm quality, as well as a higher rate of erectile dysfunction (ED). A 2007 study of 1,667 men ages 40 and up found that an increase in BMI was associated with a decrease in testosterone. And according to a 2012 study out of Cornell University, men with a waist size of more than 40 inches (the strongest single predictor of developing symptoms of testosterone deficiency) were more likely to have ED.