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High-fibre diets may affect fertility

8 February 2010
Appeared in BioNews 544

Women who eat too much fibre may ovulate less and have lower oestrogen levels, according to a recent study. The researchers examined the link between fibre consumption and hormone concentrations in 250 women aged 18 to 44 and found that those who reported eating the recommended 20g to 35g of fibre a day had the lowest blood concentrations of oestrogen and other reproductive hormones. A roughly 10-times higher risk of having 'anovulatory' menstrual cycles (where the ovaries fail to release an egg) was also linked to high fibre intake, especially fibre from fruit.

The researchers, led by Audrey Gaskins from the National Institute of Child Health and Human Development (NICHD), Rockville, Maryland, US, published their findings in the American Journal of Clinical Nutrition, making sure to point out that their results do not mean that high-fibre diets are a bad thing - after all, they have been linked to many health benefits such as lower risks of diabetes, heart disease, breast cancer and colon cancer. However, the team do believe their findings 'call into question' whether the current regulations are best for those women who are trying to become pregnant.

All of the 250 women in this study were healthy, and having regular menstrual periods. But the women who reported the highest fibre intake (22g a day or more) were found to be more likely to have at least one anovulatory cycle over two months, as measured by the low levels of oestrogen and other reproductive hormones in their blood over two menstrual periods. Some 22 per cent of menstrual cycles in this high-fibre group were anovulatory as opposed to only seven per cent in the low-fibre group.

However, there are many causes for anovulation, including extreme anxiety or stress, having too little or too much body fat, taking too much exercise, thyroid gland dysfunction and polycystic ovarian syndrome - a common female endocrine disorder that affects approximately five per cent to ten per cent of women of reproductive age. It was only once the researchers took into account these factors, along with others such as race and calorie intake, that they arrived at the corrected estimate of high fibre intake causing a roughly ten-times higher risk of anovulation.

Ms Gaskins emphasised that, while the results were consistent with fibre disrupting some women's ovulation, they did not prove that this was the case. However, there is a biologically plausible mechanism that could explain the findings. Quite simply, high-fibre diets are known to decrease the activity of particular intestinal enzymes, in turn causing more oestrogen to be excreted from the body in faeces because less oestrogen is being reabsorbed in the colon. Whilst more studies are needed before any solid conclusions can be drawn and recommendations made, Ms Gaskins and her team believe that their results suggest that women who are trying to conceive may benefit from lowering their fibre intake.

Effect of daily fiber intake on reproductive function: the BioCycle Study
American Journal of Clinical Nutrition |  19 August 2009
How healthy eating could STOP you getting pregnant
Daily Mail |  2 February 2010
Study: High Fiber Diets May Interfere With Ovulation, Fertility
Fox News |  4 November 2009
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