High-fiber diets are associated with numerous health benefits, including lower risks of heart disease, diabetes, colon cancer, and breast cancer. Experts generally recommend that adults get 20–35 g of fiber each day, depending on their calorie intake. However, the current results do call into question whether those recommendations are best for women who are trying to become pregnant, said the researchers.
All of the women in the current study were healthy and having regular menstrual periods. Still, those who reported the highest fiber intake—22 g/day or more, in line with general recommendations—were more likely to have at least one anovulatory cycle over two 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 itself was linked to a roughly 10-times higher risk of anovulation.
The results do not prove that fiber, per se, disrupts some women’s ovulation. However, the researchers noted that it is biologically plausible. The researchers found that women with the highest fiber intakes generally had the lowest estrogen levels over the course of their menstrual periods. They also had lower levels of other reproductive hormones, including progesterone, luteinizing hormone, and follicle-stimulating hormone.
The researchers concluded that, “These findings suggest that a diet high in fiber is significantly associated with decreased hormone concentrations and a higher probability of anovulation. Further study of the effect of fiber on reproductive health and of the effect of these intakes in reproductive-aged women is warranted.”
A study published in the American Journal of Clinical Nutrition shows that women who get the recommended amount of fiber in their diets may have lower estrogen levels and ovulate less often than women who eat less fiber. Researchers found that among 250 women ages 18 to 44, those who reported eating the recommended amounts 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.