Colon cancer starts in the lining of the bowel, and studies have now found that microplastics may disrupt this lining’s frontline defence – a delicate layer of mucus that protects it from harmful microbes and toxins, says lead author Dr Rathin Gosavi, colorectal fellow at Cabrini Hospital.

“The thinning or patchiness of this mucus layer can leave the underlying cells exposed, increasing the risk of inflammation and, potentially, damage from microbial by-products. Microplastics might also disturb the balance of ‘friendly’ bacteria that produce compounds that protect the gut, and may provide surfaces for harmful bacteria to form biofilms – sticky layers of bacteria, some of which release toxins implicated in colorectal cancer.”

Still, the group is careful to stress that it’s early research: more studies are needed to confirm a clear link between microplastics and cancer.

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“Most of what we know comes from experimental models, in animals and cell systems, showing that microplastics can disrupt gut barrier function, alter the microbiome, and promote inflammation. A few small human studies have detected microplastics in colorectal tumour tissue, but we’re far from proving causation. At this stage, it’s a hypothesis worth testing, not a conclusion.”

How can we keep our gut in the best possible shape?

• Staying at a healthy weight is a good start – each year, overweight and obesity cause almost 5300 cases of cancer, including colon cancer, while physical inactivity causes 12 per cent of our colon cancers, according to Cancer Council Australia.
• Eat minimally processed foods like whole grains, legumes, vegetables, fruit and unsalted nuts – but less red and processed meat. There’s strong evidence that it causes colon cancer. The haem iron content of meat is thought to be one culprit – it makes meat red but also forms harmful N-nitroso compounds in the gut that can damage cells lining the colon, Cancer Council Australia says. Processed meats also contain preservatives, nitrates and nitrites, which form the same harmful compounds.
• Include calcium-rich foods. Research this year from Oxford Population Health in the UK linked calcium from dairy foods and non-dairy sources to a 17 per cent lower risk of colon cancer.
• Ease off on alcohol. Two drinks or more a day increases colon cancer risk, says the World Cancer Research Fund. And don’t smoke.
• Are you 45 or over? Get screened for colon cancer, says Canfell. “Uptake of home testing via the National Bowel Cancer Screening Program is the major reason for the drop in colon cancer in the over 50s. Screening can lead to early detection of polyps before they develop into cancer and also detect any existing cancers earlier.”
• As for minimising microplastic exposure, avoiding single-use plastics, especially when heating food, and reducing packaged meals is a sensible first step, Gosavi adds. “Choosing whole foods over ultra-processed ones is likely to be beneficial, not just for reducing plastic ingestion but for broader health reasons.”

Can we reduce the impact of microplastics once they reach the gut?

“The science is in its infancy,” he says. “Some pre-clinical studies suggest that diets high in fermentable fibre, from foods such as barley, oats, legumes and nuts, for example, may help restore the mucus barrier and support protective gut bacteria. Probiotics, antioxidants, or even future pharmacological strategies could also help, but we’re not there yet.

“For now, reducing exposure and promoting overall gut health, through diet, fibre intake and microbial diversity is our best approach.”

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