Walnuts boost sperm strength.
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Walnuts boost sperm strength.

If you see fatherhood in your future, you may want to work walnuts into your diet. A new study found that a daily dose of these antioxidant-rich omega-3 powerhouses helps sperm swim faster and pack more of a punch – factors that can significantly enhance male fertility.

University of California, Los Angeles researchers recruited 117 healthy men between ages 21 and 35 who had no known fertility problems and ate typical Western diets. Half of the guys snacked on 75 grams of walnuts per day (about two handfuls) while the other half refrained from tree nuts altogether. After 12 weeks, the walnut group showed better markers of sperm health, such as vitality, motility, and shape. "Vitality is a measure of how many sperm are actually alive, and motility means how well they move in a forward direction," says Wendie Robbins, lead study author and a professor at UCLA's Fielding School of Public Health. She says shape is also important because abnormally formed sperm may not move as well and can have trouble fusing with the female egg, both of which can hinder conception.

So why walnuts? For one, they're a super source of plant-based omega-3s. "Polyunsaturated fatty acids like omega-3s are critical during sperm maturation and for function of mature sperm," Robbins says. "To have motility, you need fluid membrane, and fatty acids ensure that." Walnuts' high antioxidant content also plays a role. "Sperm generate a lot of energy, which can cause oxidative damage to the cell membrane, so you need lots of antioxidants such as selenium and plant polyphenols to help prevent damage and keep them intact," she explains.

Robbins says it's high time we wised up to the fact men's dietary choices can impact fertility, especially since about 30 percent of infertility cases can be traced to a male factor. "For years we've been telling women who are thinking about starting a family to refine their diet so that by the time of conception, they're already nutritionally sound," Robbins says. "There hasn't been much science surrounding male dietary recommendations for fertility because people didn't really think about that in the past. But this research tells men that their diets matter as well." She also notes that animal studies have shown that a father's diet indeed impacts his offspring's health.

Thinking of making babies? Robbins says starting on walnuts about three months out will cover the bases, since sperm production takes about 72 days and then they need some additional time to mature. And if you're worried about packing on pounds from walnuts' calories and fat content, don't. The guys in the study were concerned too, and they didn't gain weight. "We monitored body weight very carefully because we knew this young, fit group would be body conscious," Robbins says. "Perhaps they didn't gain because they were getting the nutrients from nuts and cutting out less healthy snacks."