For years, nutritionists have rallied around the notion that "you are what you eat."
Now, new research suggests this adage might even extend to the strength and quantity of sperm.
The observation stems from a pair of studies slated for presentation Monday at the American Society for Reproductive Medicine annual meeting in Orlando, Fla., both of which highlight an apparent linkage between nutrition and semen quality.
The upshot: Diets rich in red meat and processed grains seem to impair the ability of sperm to move about, while diets high in trans fats appear to lower the amount of sperm found in semen.
"The main overall finding of our work is that a healthy diet seems to be beneficial for semen quality," said Audrey J. Gaskins, lead author of the first study. Currently a doctoral candidate in Harvard School of Public Health's department of nutrition in Boston, Gaskins' colleagues included researchers from both the University of Rochester and the University of Murcia in Spain.
"Specifically, a healthy diet composed of a higher intake of fish, fresh fruit, whole grains, legumes and vegetables seems to improve sperm motility," Gaskins explained, "which means a higher number of sperm actually move around, rather than sit still."
Gaskin's conclusions are based on work with 188 men between the ages of 18 and 22, who were recruited in Rochester. Food questionnaires were completed, and participant diets were categorized as being either "Western" in content (including red meat, refined carbs, sweets and energy drinks) or so-called "Prudent" (composed of fish, fruit, vegetables, legumes and whole grains).
Semen tests were then conducted to assess sperm movement, concentration and shape.
Although diet seemed to have no impact on either sperm shape or number, motility was impacted, with "Western" diets linked to reduced movement, even after accounting for factors such as race, smoking history and body-mass index (BMI).
Gaskins stressed, however, that more work is needed to better understand exactly how nutrition can affect sperm.
"This was a small study, and we don't know if there's something else about the men that causes them to have worse motility," she noted. "We don't know if nutrition actually causes the change. So, for now all we can say is that there's an association between nutrition and sperm quality."
On a similar front, a second study led by Dr. Jorge Chavarro, an assistant professor of nutrition and epidemiology at the Harvard School of Public Health, revealed that men who eat diets that contain a relatively high amount of trans fat had lower sperm concentration levels. What's more, the amount of trans fat found in their sperm and semen went up.
The conclusion was drawn from work with nearly 100 men, all of whom underwent a nutritional and semen quality analysis.
Even after adjusting for a wide array of factors such as age, drinking and smoking histories, BMI, caffeine intake and total calories consumed, the authors found that although trans-fat intake appeared to have no impact on sperm movement of shape, the more trans fatty acids consumed the lower an individual's sperm concentration.
Dr. Edward Kim, from the University of Tennessee's graduate school of medicine in Knoxville, reacted to both studies with enthusiasm and caution.
"I think that this research is certainly very suggestive that dietary factors may have an impact on male infertility," said Kim, who also serves as president of the Society for Male Reproduction and Urology.
"And the studies point us in a direction that suggest that a healthy lifestyle may correlate with better quality sperm," he added. "But clearly further research in this area is needed to come up with definitive conclusions."
Because both studies were presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.
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