Worried about the link between E. coli and cancer? Eat more fibre (2025)

With news this week that childhood exposure to E. coli bacteria may be partly responsible for the sharp rise in bowel cancer among under-fifties, most of us are asking what we can do to protect against both things.

The new study, published in Nature and backed by scientists at Cancer Research UK, has highlighted the potentially dangerous role of colibactin, which is produced by a strain of E. coli. The toxin is capable of causing DNA mutations in the bowel cells of under-10s, which could in turn lead to their developing cancer before the age of 50.

With bowel cancer levels among 25-49-year-olds up 52 per cent since the 90s – and “early onset” cases growing faster in England than the rest of Europe – experts have suggested this finding could be a key part of the puzzle.

However, it’s important to bear in mind that not all E. coli deserves a bad rep, explains Dr Emily Leeming, a scientist at King’s College London and author of Genius Gut: the Life-Changing Science of Eating for your Second Brain.

“Many E. coli are absolutely harmless, and I think E. coli often gets a bad name for itself because there are a couple of types which people are familiar with, for getting food poisoning,” she says. “But it’s very normal to have E. coli in your gut,” she says, adding that less than five per cent of microbes cause disease. “Most people will have that, and it’s absolutely healthy.”

Of the hundreds of E. coli strains, six are known to cause diarrhoea. These infections typically arise via consumption of contaminated food or water; contact with animals, their environment or faeces, or the faeces of an infected individual. As a rule, those who contract these strains do not require treatment beyond keeping hydrated and waiting for the gastric distress to pass, but E. coli-induced infections may require antibiotics.

The potentially dangerous colibactin is not among these six strains, instead produced by those containing a region of DNA called pks.

So what can we do to reduce our levels of colibactin? In a mouse study published in Nature last month, those with a low-fibre diet were found to have higher levels of colibactin-producing E. coli, along with greater rates of inflammation, “which is often a warning; a sign that there’s potential problems,” says Leeming. Inflammation, thought to be exacerbated by under-50s’ ultra processed food-filled diets, are deemed a driver of high bowel cancer rates.

The other thing to bear in mind is that although impact was reversed when the mice were given inulin, a type of fibre, the same research has not yet been replicated in humans. “We really, in the research, need to take it one step further and to understand this relationship more,” says Dr Leeming.

In the meantime, if you suspect you may have, or have had, E. coli-induced colibactin in your gut, what should you do?

Don’t test

“I really wouldn’t recommend doing a gut microbiome test,” Leeming advises, as they don’t actually tell you anything that’s useful or relevant. “Doing a gut microbiome test isn’t going to do anything but cost you a lot of money, and probably some unnecessary stress.”

She instead recommends looking out for warning signs: changes in bowel habits that persist longer than three weeks, blood in your stools, unexplained weight loss or stomach pains. If these arise, Leeming advises that “you absolutely do go and see your doctor, and there are screening processes to follow that up”.

Prevention is better than cure

The best course of action where harmful gut bacteria are concerned is preventative, she says. That means following a healthy diet, which “tends to mean in general that problematic bacteria like pks plus E. coli don’t get the opportunity to thrive”.

Eating a wide range of whole foods is required for a diverse gut microbiome – as is prioritising foods that are high in fibre; something few do: “Ninety three per cent of people in the UK are not eating the recommended amount of fibre a day, which is 30 grams.”

In order to work more of these gut-boosting foods into your meals, Leeming suggests a mental dietary checklist: “can you add in some more wholegrains? Can you add in some more nuts and seeds, some fruits and vegetables, beans and legumes? That fibre helps to feed your good, healthy gut bacteria, which then means that the more harmful bacteria are not able to thrive as well.”

Bring back breakfast

She advises being “fibre-smart”: a salad is all well and good, but with only 1.8g of fibre per 100g of lettuce – and 15 times as much per 100g of chia seeds – incorporating the richest sources of the nutrient will far more easily help you hit your daily fibre target.

Prebiotic fibres found in the likes of leeks, garlic and onions; polyphenol-rich black beans and pumpernickel rye bread also feed good gut bacteria, and keep you feeling fuller for longer. While the likes of intermittent fasting often mean breakfast falls by the wayside, it’s is a valuable source of fibre, says Leeming. “Studies show that those who skip breakfast tend to have lower fibre intake and other nutrients than people who do have breakfast.”

Get outside

Our sedentary, indoor lifestyles are also having a deleterious effect on our microbial diversity. Getting outside and interacting with nature is key to overturning this: a 2018 study published in Future Microbiology showed that “dipping hands in soil daily for two weeks changed the skin and gut microbiomes of the study’s participants, indicating a correlation between natural interactions and the diversity of the gut microbiota”.

The team behind this week’s study confirmed that 30-40 per cent of UK and US children had colibactin-producing E. coli in their bowels, and are now looking to develop a colibactin stool test that could one day identify those at higher risk of early-onset bowel cancer. If colibactin is found to be a driver of the disease, more research into how the bacteria arose, children’s exposure and whether probiotic therapies can replace the harmful microbes within the gut will need to be explored.

Leeming remains optimistic about where the research is headed. “It’s very important,” she says of digging into the strain’s causes – and potential cures. “Hopefully we have more answers for people in the future, but there’s still a lot of unknowns.”