Other studies, the researchers noted, show that obesity may damage male fertility, and that putting on fat leads to lower testosterone levels and higher estrogen levels. In the Hammoud study, done over a two-year period, the team examined 390 men who went for help with infertility. Of these men, 24 percent had a normal weight (defined as a body mass index of less than 25), 43 percent were overweight, and 33 percent were obese (having a BMI of 30 or greater). Of the 390, 10.5 percent had low sperm counts.
As BMI rose, the likelihood of having a low sperm count did also. The obese in the study had a 3.3 times larger chance of a low sperm count. In addition, they were 3.4 times more likely to have a low count of progressively mobile sperm - sperm that swim forward in a straight line - than their normal-weight peers. Obese men also had a 1.6 times greater risk than men of normal weight of exhibiting a high percentage of irregularly shaped sperm.
While the study failed to show any statistically significant tendency toward erectile dysfunction with increasing BMI, the team noted that other research has established such a link. The researchers speculated that, while a higher rate of poor sperm quality would be expected among men seeking infertility help, the correlation between obesity and sperm problems probably translates into the general population, as well.