The researchers, from the University of California at Los Angeles, tested a bunch of healthy, young men. Some of them ate walnuts while others didn't. After performing tests on them, the walnut-eating group had improved semen quality over the control group.
Their paper "Walnuts Improve Semen Quality in Men Consuming a Western-Style Diet: Randomized Control Dietary Intervention Trial" (doi: 10.1095/biolreprod.112.101634) is authored by Wendie A. Robbins, Lin Xun, Leah Z. FitzGerald, Samantha Esguerra, Susanne M. Hennin,g and Catherine L. Carpenter, all from the University of California Los Angeles.
The paper was published in the journal Biology of Reproduction, appearing online for the first time on August 15, 2012.
Their abstract states, "We tested the hypothesis that 75 gm [grams] of whole-shelled walnuts/day added to a Western-style diet of healthy young men would beneficially affect semen quality."
They were then studied for 12 weeks, with some of the men (59) eating walnuts while others (58) didn't. The walnut-eating group ate 75 grams of whole-shelled walnuts a day, while the control group did not add walnuts to their usual diet.
The researchers analyzed such factors as blood serum and sperm fatty acid (FA) profiles, sex hormones, and serum folate.
The group concluded, "The group consuming walnuts (n=59) experienced improvement in sperm vitality, motility, and morphology and the group continuing their usual diet but avoiding tree nuts (n=58) saw no change."
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