Diet & Fertility | Men's Health Blog

Junk Food May Impair Fertility


Like father, like son…like sperm, at least when it comes to getting sluggish after a heavy meal. That’s the conclusion of a recent study out of the Harvard School of Public Health, which found that when men eat fatty, unhealthy food, their sperm lose the ability to move vigorously enough to make the journey all the way up the ovarian tube.1 A related study found that eating trans fats reduces sperm count. Added together, these facts seem to indicate that a junk food diet may lead men to male infertility. So it would seem that Tom Jones was actually practicing birth control rather than seduction in his famous eating scene.

The first study involved 188 men between the ages of 18 and 22. The subjects answered questions about their diets and, based on their responses, were split into two categories. The first group included those who enjoyed “Western diets,” rich in red meats, sweets, refined carbohydrates and soft drinks. The other group followed the aptly named “Prudent” diet, which looks a lot like the Mediterranean diet with an emphasis on fish, fruit, vegetables, legumes and whole grains.

Then, all the subjects submitted semen samples. The researchers analyzed the samples for concentration of sperm, shape of sperm, and the ability to move. While diet had no effect on either shape or concentration of sperm, it sure did impact the ability of the sperm to move toward an egg. The men with healthier diets had sperm that outpaced the sluggards by 11 percent.

While on the one hand, the researchers caution that the study is too small and preliminary to absolutely prove that nutrition damages sperm, they do assert that, “For now all we can say is that there’s an association between nutrition and sperm quality.”2 Lead researcher Audrey J. Gaskins thinks that association might be the result of antioxidants in the better diet. “The more natural antioxidant intake you have, the better balance you’ll have between the antioxidants and reactive oxygen species, which decrease sperm quality,” she says.

In the second study, the Harvard School of Public Health researchers looked specifically at the relationship between sperm quality and trans fat content in the diet. After reviewing the diets and sperm of 100 subjects, the researchers concluded that those with the highest intake of trans fat also had the lowest sperm count, although neither sperm shape nor motility seemed affected in this case. The trans fat junkies had sperm counts averaging 48 million per milliliter, versus 79 million/ml for those with the lowest intake of trans fat.3 Startling as the discrepancy is, the researchers say that the lower sperm count still falls within the normal range. Two things should be noted here. First, is what doctors call normal truly “healthy” normal or just what we’ve come to accept as normal because too many men are on unhealthy diets. And second, it should be noted that the researchers were measuring for man-made trans fats, not natural trans fats such as CLA, which may actually improve the performance of sperm.4

If, on the other hand, you’re a guy who wants to maintain a high level of fertility but can’t see giving up the burgers and shakes, there’s another study just out and about that you might find relevant. This one comes from Yamaguchi University in Japan, where 215 men gave semen samples and filled out questionnaires about their exercise routines.5 The men were of similar age and had similar body mass indexes. It turns out that those who did moderate exercise such as brisk walking had the best sperm motility by a long-shot, with only 14 percent falling into the “Low” motility category, meaning their sperm had the best chance of making it up the fallopian tube. It would seem that your sperm exercises right along with you. The couch potatoes had the most sluggish sperm, with 31 percent at “Low motility,” and in a big surprise, the vigorous exercisers were almost as sluggish at 27 percent.

While it’s somewhat distressing to discover that intense exercise may hinder sperm vitality given how essential exercise is to health, earlier studies do indeed indicate that some forms of exercise might be more damaging than others.6 Bike riding, in particular not only damages sperm motility but also leads to a low sperm count. In fact, a study out of Boston University last year found that men who ride bikes more than five hours a week are twice as likely to have a low sperm count and impaired sperm motility. The director of that study explains, “It’s possible that trauma or temperature increases in the scrotum may explain the relationship between biking and semen health, “but more research is needed to investigate these mechanisms further.”

Now there’s an argument for investing in an extra-cushy seat for your Schwinn Voyager. And apparently, other studies have linked bike riding with urinary problems, too. But the good news is that the Boston University study found no damaging effects to sperm from other forms of exercise, so you can choose which study you want to pay attention to if you wish to impregnate your partner. If you want to be lazy, the Japanese study gives you a good excuse to limit your exertion to a walk in the park. If you prefer to run marathons or play a few rounds of tennis daily, opt for the BU results. Then again, this isn’t the first time research has found that when it comes to exercise, too much of a good thing may be bad. Extreme exercise has been associated with cognitive decline in women, for example.

In any event, no matter how your sperm fare, you’re going to feel a whole lot better if you eat right and exercise, at least moderately. You’ll probably have more interest in sex and more ability to perform. You’ll be more attractive to your mate. And assuming you do succeed in getting your partner pregnant, you’ll have a far better chance of living long enough to argue politics with your kids when they grow up.


1 Shih, Cynthia. “HSPH Study Says Better Diet Leads to Healthier Sperm.” 20 October 2011. The Harvard Crimson. 20 October 2011. <>

2 Melnick, Meredith. “Could a Healthy Diet Boost Sperm?” 20 October 2011. Time/Healthland. 20 October 2011. <>

3 Susman, Ed. “Healthy Diet Boosts Semen Quality.” 17 October 2011. Med Page Today. 20 October 2011. <>

4 Veaute C, Andreoli MF, Racca A, Bailat A, Scalerandi MV, Bernal C, Malan Borel I. “Effects of isomeric fatty acids on reproductive parameters in mice.” Am J Reprod Immunol. 2007 Dec;58(6):487-96. <>

5 “Sperm Moves Best for Moderate Exercisers: Study.”  19 October 2011. US News & World Report: Health. 20 October 2011. <>

6 McCook, Alison. “Most exercise not linked to sperm health.” 9 December 2010. Reuters. 20 October 2011. <>

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