 In 1992, a controversial paper was published suggesting sperm counts have been dropping around the world over the last 50 years. However, this remains a matter of debate. It's notoriously difficult to determine sperm counts in a general population for an obvious reason. If you go ask men for samples, less than 1 in 3 tend to agree to participate. Finally, though, a study of tens of thousands of men studied over a 17-year period, and they did indeed find a significant decline in sperm concentration, about a 30% drop, as well as a drop in the percentage of normal-looking sperm. Most look normal in the 90s, but more recently, that's dropped to less than half. This may constitute a serious public health warning. Semen quality may actually be related to life expectancy. In a study of more than 40,000 men visiting a sperm lab during a 40-year period, they found a decrease in mortality associated with increasing semen quality, suggesting that semen quality may therefore be a fundamental biomarker of overall male health. So declining sperm counts could be like canary in the coal mine, for us, and future generations. Even when defective sperm are capable of fertilizing an egg, creating a child with abnormal sperm may have serious implications for that child's future health. What role may diet play? In a previous video, I profiled a first-of-its-kind Harvard study, suggesting that a small increase in saturated fat intake was associated with a substantially lower sperm count. But not all fat was bad. Higher intakes of omega-3s were associated with more favorable sperm shape. This may help explain why researchers at UCLA were able to improve sperm vitality movement and shape by giving men about 18 walnuts a day for 12 weeks. Though walnuts, as a whole food, have more than just omega-3s, but lots of other important micronutrients. In a study of men aged 22 through 80, older men who ate diets containing lots of antioxidants and micronutrients, for example vitamin C, had the genetic integrity of sperm from much younger men. The antioxidants we eat not only end up in our semen, but are concentrated there. The amount of vitamin C ends up nearly 10 times more concentrated in our testicles than the rest of our bodies. Why? Because sperm are highly susceptible to damage induced by free radicals, and accumulating evidence suggests that this oxidative stress plays an important role in male infertility. So we should eat lots of antioxidants, which is to say, eat lots of fruits and vegetables. Why not just take antioxidant pills? Because in pill form, antioxidants may have unexpected adverse effects. Some more fruits and vegetables, and perhaps less meat and dairy, which is where most saturated fat is found. But the Harvard data were considered preliminary. They studied fewer than 100 men, but it was the best we had until now. The higher the saturated fat intake, the lower the sperm count, up to a 65% reduction in total sperm count. These findings are of potential great public interest, because changes in diet over the past decades may be part of the explanation for the recently reported high frequency of subnormal human sperm counts. In any case, the current findings suggest that adapting dietary intake towards eating less saturated fat may be beneficial for both general and reproductive health.