Eating about two handfuls of walnuts a day may provide men the added boost they need to improve their fertility, according to a breakthrough study by researchers at the UCLA School of Nursing.
Findings from the study, "Walnuts Improve Semen Quality in Men Consuming a Western-Style Diet: Randomized Control Dietary Intervention Trial," are published Aug. 15 in the "papers in press" section of the peer-reviewed journal Biology of Reproduction.
This is the first study to look at the effects of a plant source of omega-3 on sperm, the researchers say. Statistics from the American Society for Reproductive Medicine show that one in six couples is infertile, with about 40 percent of these cases due to a male factor.
The 12-week study involved 117 men between the ages of 21 and 35, who were divided into two groups. One group added 75 grams of whole-shelled walnuts to their diet daily. The other group continued their usual diet but avoided eating tree nuts. Both groups ate a typical Western-style diet.
"We found a significant improvement in sperm parameters in the group that consumed the walnuts," said Wendie Robbins, a professor at the UCLA School of Nursing and UCLA's Fielding School of Public Health and lead author of the study. "The men who ate no tree nuts saw no change.
"Women are not the only ones who should be paying attention to what they eat when they are trying to get pregnant," she added. "This study shows that what men eat is important too."
Food has been linked to human reproductive success throughout history. And while dietary habits and essential nutrients that promote successful reproductive outcomes for women have been identified, the habits and nutrients that can improve men's reproductive fitness are less clear, the researchers say. In particular, evidence is limited for men who routinely consume Western-style diets that may lack optimal nutrients needed for health, sperm and fertility.
"Walnuts provide a particularly rich source of a-linolenic acid, a natural plant source of omega-3, which we suspect may have been responsible for the improvements we observed," said study co-author Catherine Carpenter of the UCLA Center for Human Nutrition and UCLA schools of nursing and medicine.
The next step, according to the researchers, is to work with couples who are attending infertility clinics to determine if placing men on a walnut diet results in better success conceiving.
The study was funded through a grant from the California Walnut Commission and the UCLA Fielding School of Public Health's Center for Occupational and Environmental Health.
In addition to Robbins and Carpenter, study co-authors included Lin Xun, Leah FitzGerald and Samantha Esguerra of the UCLA School of Nursing and Susanne Henning of the David Geffen School of Medicine at UCLA and the UCLA Center for Human Nutrition.
University of California Los Angeles