In this Harvard study involving 18,555 married women without a history of infertility, results indicate that higher intake of protein from vegetable sources instead of animal sources may lower the risk of ovulatory infertility. During 8 years of follow up, 438 women reported ovulatory infertility. The 20% of women who ate the highest amount of animal protein had a 39% increased risk of ovulatory infertility, compared with the lowest 20%. On the other hand, those in the highest 20% for vegetable protein intake had a 22% lower risk of ovulatory infertility, compared with the lowest 20%. Substituting vegetable for animal protein for 5% of caloric intake was associated with a 50% reduced risk of ovulatory infertility. Thus, the authors of this study conclude, "Replacing animal sources of protein with vegetable sources of protein may reduce ovulatory infertility risk."
"Protein intake and ovulatory infertility," Chavarro JE, Willett WC, et al, Am J Obstet Gynecol, 2008; 198(2): 210.e1-7