It starts in the gut

A post in The Guardian today includes the news that gut bacteria may influence bowel cancer risk. How confusing! For years we’ve been taught that cancer starts with genetic mutations. So how can bacteria be involved?

It’s widely accepted that your gut bacteria are important for health. Establishment of a ‘resilient’ microbiota starts with a natural birth and breastfeeding, though we have recently learned that conditions inside the womb are not sterile. The community of organisms (bacteria, fungi, viruses, etc) that populate your gut operates at the intersection between your genes and the environment, affecting a range of organs and playing an important role in health and ageing.

The communal effect of the microbiome can be positive or negative, and we have known for some time that a ‘dysbiotic’ or imbalanced microbiome can play a role in initiation and progression of cancer. An imbalanced or sparse gut flora can promote low grade chronic inflammation, intestinal permeability, production of toxic bile acids and so-called ‘genotoxic’ metabolites that can inhibit natural cell death and stimulate cell proliferation – all linked to an increased risk of carcinogenesis. Frequent antibiotic use – which tends to destroy bacterial colonies whether ‘good’ or ‘bad’ – is associated with an increased risk of breast cancer.

The impact of the microbiome has been linked not only to local malignancy (i.e. cancers of the digestive tract) but also to distal malignancies such as breast cancer. For example, the gut houses bacteria that play a crucial role in oestrogen metabolism and an imbalance in these organisms has been linked to oestrogen receptor positive breast cancer.

On a more positive note, gut microbes act on our behalf to transform and activate many of the anti-cancer molecules that we eat and may help maximise the effects of treatment. Many of the foods we regard as healthy are reliant on the the right gut flora to be transformed into cancer-fighting compounds. There are even studies that show that a healthy microbiome can improve the effectiveness of chemotherapy.

When we think of the microbiome we tend to think primarily of the gut, but all membranes that interface with the external environment have an associated microflora, even the breast. An observational study of 71 women aged 19 to 90 undergoing breast surgery for benign and malignant disease found significantly different bacterial profiles between healthy and cancerous tissue, and a further study showed that the breast microbiome is directly impacted by diet quality, and may even be useful as a diagnostic tool .

More research is needed to clarify precise mechanisms of interaction between the microbial community and carcinogenesis so it’s great to see that studies are ongoing. Meanwhile, we need to be aware that the combined impact of stress and treatment that accompanies diagnosis tends to play havoc with the microbiome so it makes sense to optimise your digestion and nurture your gut flora as much as you can for prevention and recovery.

  • Eat plenty of ‘prebiotic’ foods that act as fuel for gut organisms – found in onions, leeks, garlic, chicory, dandelion greens, Jerusalem artichokes, sweet potatoes, berries, oats, apples, cocoa, seaweed, linseed and other seeds, nuts and legumes.
  • Keep your microflora topped up with fermented foods (yoghurt, cheese, kefir, kombucha, kimchi, sauerkraut etc.) and a daily probiotic.
  • Avoid sugar, sweeteners and seed oils.
  • Avoid gut irritants – alcohol and wheat tend to be top of the list.
  • Avoid antibacterial products and antibiotics whenever you can.

References (in order of relevance):

Stinson, L.F., Boyce, M.C., Keelan, J.A., et al. 2019. The not-so-sterile womb: Evidence that the human fetus is exposed to bacteria prior to birth. Frontiers in Microbiology 10. doi:10.3389/fmicb.2019.01124

Kerr, C., Grice, D., Tran, C., Bauer, D., Li, D., Hendry, P. and Hannan, G., 2014. Early life events influence whole-of-life metabolic health via gut microflora and gut permeability. Critical reviews in microbiology, 41(3), pp. 326–40.

Sheflin, A., Whitney, A. and Weir, T., 2014. Cancer-promoting effects of microbial dysbiosis. Current oncology reports, 16(10).

Kwa, M., Plottel, C.S., Blaser, M.J. and Adams, S., 2016. The intestinal microbiome and estrogen receptor–positive female breast cancer. Journal of the National Cancer Institute, 108(8), p. 29. doi: 10.1093/jnci/djw029.

Velicer, C., Heckbert, J. et al., 2004. Antibiotic use in relation to the risk of breast cancer. Journal of the American Medical Association, 291(7) pp.827-835.

Bultman, S.J., 2016. The microbiome and its potential as a cancer preventive intervention. Seminars in Oncology, 43(1), pp. 97–106. doi: 10.1053/j.seminoncol. 2015.09.001.

Viaud, S., et al., 2013. The intestinal microbiota modulates the anticancer immune effects of cyclophosphamide. Science, 342(6161) pp. 971-976. doi:10.1126/science.1240537

Chan, A., et al., 2016. Characterisation of the microbiome of nipple aspirate fluid of breast cancer survivors. Scientific Reports, 6:28061.

Shively, C., et al., 2018. Consumption of Mediterranean versus Western Diet Leads to Distinct Mammary Gland Microbiome Populations. Cell Reports 25(1) pp:47-56.

Shaheed, S., Tait, C., et al., 2018. Evaluation of nipple aspirate fluid as a diagnostic tool for early detection of breast cancer. Clinical Proteomics 15:1.


Original article:


The Guardian

Published by

Dawn Waldron

Highly experienced nutritional and nutrigenomic therapist helping people optimise diet, lifestyle and gene expression for health and happiness after breast cancer.