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A new study revealed that a fibre-rich diet may not be recommended for women who are trying to become pregnant.
Women who get the recommended amount of fibre in their diets may have lower oestrogen levels and ovulate less often than women who eat less fibre, a new study suggests.
Researchers found that among 250 women ages 18 to 44, those who reported eating the recommended amounts of fibre had the lowest blood levels of oestrogen and other reproductive hormones.
Anovulary menstrual cycles
Higher fibre intake, particularly from fruit, was also linked to a higher risk of having anovulatory menstrual cycles - where the ovaries fail to release an egg.
The findings, reported in the American Journal of Clinical Nutrition, do not mean that eating fibre-rich foods is a bad thing.
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 20gr to 35gr of fibre 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, write the researchers, led by Audrey J. Gaskins of the National Institute of Child Health and Human Development in Rockville, Maryland, US.
Anovulation can have various causes, including excessive exercise, having either too little or too much body fat, thyroid gland dysfunction and polycystic ovarian syndrome - a hormone disorder that is a common cause of infertility.
Women who are not ovulating regularly often have irregular menstrual periods or none at all. However, some women do continue to have periods.
10-times higher risk
All of the women in the current study were healthy and having regular menstrual periods. Still, those who reported the highest fibre intake - 22gr per 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 fibre intakes.
When the researchers accounted for other factors that could affect ovulation - including body weight, race, exercise levels and calorie intake - high fibre intake itself was linked to a roughly 10-times higher risk of anovulation.
Fibre in fruit
Looking at specific sources of fibre, the researchers also found that fibre from fruit, specifically, was most clearly associated with anovulation.
The results do not prove that fibre, per se, disrupts some women's ovulation. However, it is biologically plausible, Gaskins and her colleagues point out.
High-fibre diets, they explain, decrease activity in certain intestinal enzymes, leading to less oestrogen reabsorption in the colon. Fibre can also cause more oestrogen to be excreted from the body in faeces.
Low oestrogen levels
In line with that, the researchers found that women with the highest fibre intakes generally had the lowest oestrogen 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 findings, according to Gaskins and her colleagues, raise the possibility that women who are trying to conceive should lower their fibre intake. However, they write, more studies are needed before any recommendations can be made. - (Reuters Health, November 2009)
SOURCE: American Journal of Clinical Nutrition, October 2009.
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