Can Too Much Fiber Affect Fertility?

A Nutrition Diva listener recently wrote to me worried that she might be eating too much fiber.

I have a really high fiber diet, as I’ve found it difficult to eat less than 30g of fiber a day when eating whole, non-processed foods. I have not gotten my period in several months. (No I'm not pregnant, I take birth control pills.) My dietitian sent me a study about the effects of a high fiber diet on menstruation. I would love for you to do a podcast on how fiber intake may influence menstruation in child-bearing-age women.

The study she forwarded was actually somewhat surprising. It found that women eating even the recommended amount of fiber each day had an increased risk of anovulation. This means that they experienced a menstrual cycle in which the egg did not mature. The failure to ovulate may or may not lead to a missed period but it definitely means that you cannot get pregnant. So this study could be really important for women who are trying to conceive. 

If you're regularly missing your period for any reason, it's a good idea to at least check in with your gynecologist.

However, these findings wouldn't apply to the listener who sent them to me. Birth control pills, by design, prevent ovulation no matter how much fiber you eat. If you're taking birth control pills, then your menstrual cycle, such as it is, is being controlled by external hormones, not your diet. And it is somewhat common for women taking birth control pills to stop menstruating. But, again, this usually has nothing to do with diet. If you're regularly missing your period for any reason, it's a good idea to at least check in with your gynecologist.

But what might this study for women who are trying to get pregnant? Should they be cutting down on fiber to increase their chances?

How does fiber affect ovulation?

The study, which was published in 2009 in the American Journal of Clinical Nutrition, followed 250 women of child-bearing age through two consecutive menstrual cycles. They found that about 8 percent of the time, the women failed to ovulate. They also collected a lot of dietary information and analyzed it to see if they could spot any connections between what the women ate and their risk of anovulation. They found that the women eating the recommended amount of fiber (at least 22 grams per day) were about three times as likely to miss ovulating as all the rest.

That may surprise you but it didn't particularly surprise the researchers.  We already know that dietary fiber tends to lower circulating estrogen levels in the body. We generally think of this as a good thing. It's the reason that women who eat more fiber have a lower risk of breast cancer, for example. But for women trying to conceive,...

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