Indication: Ovulation

Source: American Journal of Clinical Nutrition, October 2009.

Research: Studies indicate that women who get the recommended amount of fiber in their diet may have lower estrogen levels and ovulate less often than women who eat less fiber. This study, involving 250 women ages 18 to 44, evaluated the potential of high fiber intake to interfere with ovulation. All of the women in the study were healthy and having regular menstrual periods.

Results: Experts generally recommend that adults get 20 to 35 grams of fiber each day, depending on their calorie intake. These study results question whether those recommendations are best for women who are trying to become pregnant, according to researchers. Among study subjects, those who reported eating the recommended amount of fiber had the lowest blood levels of estrogen and other reproductive hormones. Higher fiber intake, particularly from fruit, was also linked to a higher risk of having anovulatory menstrual cycles, where the ovaries fail to release an egg. Those who reported the highest fiber intake—22 grams per day or more, in line with general recommendations—were more likely to have at least one anovulatory cycle over 2 months. The researchers gauged anovulation by measuring the women’s reproductive hormone levels over two menstrual periods. Of the total menstrual cycles in this group, 22% were anovulatory, compared with 7% among women with lower fiber intakes. When the researchers accounted for other factors that could affect ovulation—including body weight, race, exercise levels and calorie intake—high fiber intake was linked to a roughly 10-times higher risk of anovulation. Researchers also found that fiber from fruit, specifically, was most clearly associated with anovulation. According to researchers, high-fiber diets decrease activity in certain intestinal enzymes, leading to less estrogen reabsorption in the colon. Fiber can also cause more estrogen to be excreted from the body in feces. Researchers concluded that findings raise the possibility that women who are trying to conceive should lower their fiber intake. However, more studies are needed before any recommendations can be made.