From green bananas to a glass of milk, the simple diet tweaks PROVEN to cut the chances of bowel cancer, as experts reveal the cheap daily supplement that can reduce risk by 58pc

It was an announcement that reverberated around the world. Last month, American scientists revealed a startling theory behind a medical mystery that has baffled doctors and alarmed the public – the surge in bowel cancer among young people.

Long thought of as a disease of old age, colorectal cancer is increasingly striking adults in their 20s, 30s and 40s, and the culprit, researchers suggest, might be something as mundane as a common food poisoning bug.

Nearly 17,000 people die from bowel cancer each year – and while around 5 per cent are aged 25 to 49, that figure is steadily rising.

Those affected include the late campaigner Dame Deborah James, who died aged 40 in 2022. Yet diagnoses are falling in older age groups. People born in 1990 are three times more likely to develop certain tumours – including bowel cancer – than those born in the 1950s. Experts have blamed sugar, ultra-processed foods and antibiotics, but without conclusive proof. Until now.

Researchers at the University of California San Diego have a suspect: E. coli, a foodborne bacterium that infects nearly 40,000 people every year.

By analysing tumour DNA from more than 900 patients, they found a pattern of mutations in the guts of young people with colon cancer. They were caused by colibactin – a toxin produced by certain strains of E. coli that can cause cancer by damaging cell DNA. And the harm may start during childhood development after exposure to it.

It’s a frightening prospect, especially as there’s no test or vaccine, making it difficult to prevent. But there are ways to prevent bowel cancer – and it’s not just quitting smoking or cutting back on booze (though that certainly helps).

Simply taking a daily vitamin D supplement could reduce the risk by 50 per cent. Or ditching your morning sausage sandwich – a treat that may raise your risk by up to 18 per cent. ‘Too many young people don’t realise they can get bowel cancer, let alone they can do something about it,’ says Dr Claire Arthur, consultant oncologist at The Christie hospital. ‘But around half of all cases are actually preventable.’

Here are simple ways to reduce your risk of developing it...

Experts say the best thing you can do to reduce your risk of bowel cancer is affordable and readily available: fibre.

Bowel Cancer UK estimates that a lack of fibre is behind 28 per cent of all cases in the UK. Yet just 9 per cent of adults eat the recommended 30g a day. The nutrient is found in wholegrain cereals, beans, pulses, nuts, seeds, and fruit and vegetables.

Green bananas are also a good option as they contain more fibre than ripe ones.

Fibre is a type of carbohydrate in plants, but unlike sugar and starch it isn’t absorbed by the body. Instead, it keeps the gut healthy and functioning properly.

A recent study found mice infected with colibactin-producing bacteria were less likely to develop pre-cancerous growths when on a high-fibre diet.

‘It’s really good for our digestive system full stop,’ says Dr Arthur. ‘But fibre is especially good at reducing the risk of cancerous tumours from developing in the bowel.’

Fibre not only helps to flush harmful substances from the bowel in your stools, it also feeds gut bacteria that produce butyrate, a fatty acid which may lower tumour risk.

Dr Alasdair Scott, a gut specialist and science director at Selph – a health-testing firm – says high fibre intake is one of the few ways to counteract harmful E. coli in the gut.

‘There’s not much people can do if the E. coli bacteria does contribute to early onset colon cancer,’ he says. ‘But we do know that a high-fibre diet can protect against the type of mutation that causes tumours to develop.’

Another easy way to lower bowel cancer risk is to reduce meat intake, says Dr Adam Haycock, consultant gastroenterologist at the private London clinic OneWelbeck.

Research has shown both natural and added chemicals in red and processed meats can make them carcinogenic. A 2015 World Health Organisation study even classed processed meats in the same cancer risk bracket as tobacco smoking and asbestos, saying just 50g of processed meat a day (one sausage, two ham slices or a couple of bacon rashers) increases the risk of colorectal cancer by 18 per cent.

Red and processed meat, such as steak, salami and chicken nuggets, are linked to roughly 13 in every 100 colon cancer cases every year.

Another issue is how meat is cooked, adds Dr Haycock. Grilling, barbecuing and pan-frying red meat at high temperatures can form chemicals – heterocyclic amines and polycyclic aromatic hydrocarbons – known to damage DNA and increase cancer risks.

‘Most red meats are cooked using these methods,’ said Dr Haycock. ‘If you’re eating red or processed meats less than once a week, you’re probably fine. But twice a week or more and you’ll increase your risk of bowel cancer.’

Experts are increasingly worried about ultra-processed foods (UPFs) – ready-made products such as bread and cereal that are nearly two-thirds of the average British diet.

Dr Chris van Tulleken, author of Ultra-Processed People, defines them as anything wrapped in plastic and made with at least one ingredient you wouldn’t find in a typical kitchen.

A study published last week in the American Journal of Preventive Medicine linked high UPF consumption to up to 14 per cent of early deaths in the UK.

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These foods may also seriously damage our digestive systems, warns Professor Sir Neil Mortensen, a leading colorectal surgeon at Oxford and former president of the Royal College of Surgeons. ‘The increase in young onset colorectal cancer coincides with the increase in processed foods around the world,’ he says.

‘We think the connection could be due to emulsifiers in many UPFs. These are a detergent of sorts that erode the protective layer of mucus lining the bowel. The bacteria in the bowel then can reach the cells of the bowel and cause mutations.’

UPFs tend to be high in unhealthy fats and sugars and low in fibre.

But some, marketed as healthy options – such as ready-made salad dressings or granola bars – can still contain UPF ingredients such as emulsifiers that damage gut health.

‘What’s scary about a lot of these young people getting bowel cancer is that they’re not obese – they’re people who do all the right things,’ Professor Mortensen says.

Research from scientists in Hungary published last month suggests vitamin D could have an incredible effect on colon cancer. Analysing 50 previous studies involving more than 1.3 million patients, they discovered that people with an adequate intake of vitamin D were up to 58 per cent less likely to develop colon cancer.

They also found that taking a vitamin D supplement was specifically linked to a 4 per cent reduced risk of colon cancer for every 2.5micrograms consumed, as the vitamin is believed to boost the immune system – helping it to more accurately identify and suppress cancer cells.

‘We know for certain that people with recommended levels of vitamin D are less likely to get cancer and more likely to recover from it if they do,’ said Dr Haycock.

We get vitamin D from foods such as oily fish and egg yolks, and produce it in our skin when exposed to sunlight – earning it the nickname the ‘sunshine vitamin’. But the wavelength of sunlight in the British winter is not enough for people to make it. ‘Everyone becomes deficient in the winter in Britain,’ says Dr Haycock. ‘It’s the only supplement I now recommend everyone takes.’

According to University of Oxford researchers, eating calcium-rich foods – for example, milk and yogurt – can lower the risk of bowel cancer. The same is also true for non-dairy calcium sources such as dark green leafy vegetables, including spinach and kale.

This may be due to the way calcium binds to certain acids in the colon to form a harmless ‘soap’ that stops them from damaging the gut’s lining by cleaning them out and preventing them from building up. Just one glass of milk a day, the scientists found, was enough to cut the risk of bowel cancer by 14 per cent.

And yogurt has a similar effect. A Boston-based study on more than 150,000 participants, spanning several decades, said consuming two or more servings of yogurt per week was associated with a lower risk of an aggressive colorectal cancer called Bifidobacterium-positive proximal colon cancer – located on the right side of the colon and linked to the bacteria, Bifidobacterium.

Walnuts are yet another bowel superfood, having been found to reduce inflammation (a damaging immune response linked to cancer) in the stomachs of patients at high risk of developing the disease and to even increase cancer-fighting immune cells.

University of Connecticut School of Medicine researchers gathered 39 patients aged between 40 and 65 with an elevated risk of colon cancer, and gave them a handful of walnuts each day for three weeks. In the end, all participants had a reduced concentration of inflammation proteins in their urine and higher levels of a protein called peptide YY, associated with preventing colorectal cancer.

Walnuts are thought to reduce the risk of bowel cancer due to their high ellagitannin level – a plant-based chemical that can reduce cancer-causing inflammation when broken down by the gut.

Grabbing just a ‘handful every day’, said one of the report’s authors, Dr Daniel Rosenberg, could contribute to a reduced cancer risk. Just make sure they’re not the deep-fried, honey-roasted or salted kind, warns Dr Haycock.

The best way to avoid advanced, potentially deadly bowel cancer is catching it early.

When caught at stage 1, the survival rate is around 90 per cent. But if it spreads elsewhere, that number drops sharply to just 13 per cent.

If you’re 54 to 74, make sure to take up the offer of the NHS’s free at-home test every two years. It’s simple, quick, and could be life-saving, says Dr Arthur: ‘It’s a quick and easy test. But it’s also important to watch out for symptoms, as it’s not always 100 per cent accurate.’

Blood in stools, changes in bowel habits and ongoing abdominal pain shouldn’t be ignored. ‘Younger patients will often attribute these to other things – like diet, exercise or stress – but if these subtle symptoms are persisting beyond several weeks, it’s important to see your GP,’ Dr Arthur adds.

‘Most of the time it won’t be cancer, but let your doctor make that judgment. And don’t ever be embarrassed to bring it up.’