On the other hand, men who had a higher intake of omega-6 polyunsaturated fats had greater sperm motility, and a higher intake of omega-3 polyunsaturated fats was related to better sperm "morphology" -- the size and shape of sperm.
"Whether these finding are important may depend on an individual male," Attaman said.
For example, a 40 percent difference is large, but may be important to some men and not to others. If a man has a marginal sperm concentration, such as 25 million sperm per milliliter, a 40 percent reduction could bring his sperm count down to 15 million per milliliter, which is abnormal, Attaman said.
But, if a man's sperm count is closer to 100 million per milliliter, a 40 percent decrease would still maintain a normal sperm count of 60 million per milliliter, she said.
"That would be unlikely to make a difference in fertility potential," Attaman said.
Saturated fat is the main dietary source of high blood cholesterol and can be found mostly in foods from animals and some plants, such as beef, veal, lamb, milk and cheese. Monounsaturated fats are found in vegetable oils such as olive oil, canola oil, peanut oil, sunflower oil and sesame oil. Other sources include avocados, peanut butter, and many nuts and seeds, according to the American Heart Association.
Polyunsaturated fats are found in fish, whole grains and some seeds and nuts.
Dr. David Katz, director of the Prevention Research Center at Yale Unioversity School of Medicine, said that "this is a small study of association between variations in dietary intake, and variations in sperm quantity and function. It does not directly prove cause-and-effect."
Some of the findings, such as an inverse association between monounsaturated fat intake, which is a staple of the Mediterranean diet, and sperm count are counter-intuitive, he noted. The association between polyunsaturated fat intake, and in particular balanced intak
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