A study investigated the correlation between fiber consumption and oestrogen levels in 29 post-menopausal women recently diagnosed with invasive breast cancers that tested positive for both oestrogen and progesterone (Zengul et al., 2020).
Typically, oestrogen circulates throughout the body until it reaches the liver, where it undergoes inactivation via conjugation. The deactivated oestrogen is then transported to the intestine for elimination through stool.
Certain bacteria produce beta-glucuronidase, which re-activates oestrogens in the gut. These activated oestrogens are reabsorbed and influence oestrogen metabolism which is associated with hormone-dependent cancers, such as breast cancer.
It was hypothesised that higher levels of dietary fibre will be associated with lower abundance of intestinal microbiota that promote beta-glucuronidase activity (Zengul et al., 2020).
Stool samples were collected using a microbiome analysis fecal DNA extraction as well as blood draws to test oestrogen. Dietary intake was taken for two days that represented normal eating habits for one weekday and one weekend day.
The study found that higher levels of total and soluble dietary fibres correlate with lower levels of Clostridium hathewayi sp. and Clostridium (Erysipelotrichaceae family), respectively. These bacteria promote beta-glucuronidase activity.
One species that increases beta-glucuronidase activity was higher with greater amounts of insoluble fibre intake. This highlights the intricate nature of this regulatory system. Beta-glucuronidase enzyme does have an important role in hormone metabolism which may relate to this increase (Zengul et al., 2020).
A limitation of this study was the small number of participants. In addition, 82% of the participants were obese. Obesity increases oestrogen production in the body and may have impacted the results.
The average fiber intake was 14g, falling short of the recommended 25g/day according to Australian dietary guidelines. The frequency of daily bowel movements, which could offer valuable insights into oestrogen elimination through excretion, was not recorded.
Zengul, A. G., Demark-Wahnefried, W., Barnes, S., Morrow, C. D., Bertrand, B., Berryhill, T. F., & Frugé, A. D. (2020). Associations between Dietary Fiber, the Fecal Microbiota and Estrogen Metabolism in Postmenopausal Women with Breast Cancer. Nutrition and Cancer, 73(7), 1–10. https://doi.org/10.1080/01635581.2020.1784444