The worrying new theory behind the rise of bowel cancer in young people – and an alarming link to antibiotics

Published: 06:58 EDT, 19 October 2026 | Updated: 07:12 EDT, 19 October 2026

Katy Lander was constantly bloated, exhausted and suffering stomach pain when she first went to her GP. The 32-year-old was told she was probably run down and stressed.

‘I had no energy whatsoever and had this constant bloating all the time,’ says Katy, a GP admin assistant from a village near Worksop, Nottinghamshire.

‘When the doctor said it was stress it kind of made sense: I had a two-year-old and a six-year-old, we were renovating a house, I’d been planning a wedding all year and I was getting married in a couple of months’ time,’ she says.

But around seven months later, she also started experiencing changes in her bowel habits – sometimes needing to rush to the loo immediately after eating, while at other times being constipated for the entire day.

Katy, a mother of two, contacted her surgery again, but was told she would have to wait four weeks for a telephone appointment.

‘I was getting really worried and anxious,’ she recalls – ‘and didn’t feel any better’.

By the time she finally spoke to a GP in June 2024, she’d started noticing blood in her stool and was suffering severe stomach pain on and off.

She told her doctor she was frightened this meant she had bowel cancer – but he reassured her that she was too young and that it was more likely to be irritable bowel syndrome. But he asked her to come into the surgery for an examination a few days later – he also arranged a FIT test, which checks a stool sample for blood, a possible sign of bowel cancer.

Katy Lander was constantly bloated, exhausted and suffering stomach pain when she first went to her GP. The 32-year-old was told she was probably run down and stressed

Katy returned the sample to the surgery the following morning – and the next day was referred for an urgent colonoscopy, a camera examination of the bowel, which found 13 polyps, small growths as well as a large mass.

Katy recalls: ‘I had a bad feeling about it.’

Her fears were confirmed when after biopsies and a CT scan, Katy and her husband, Ollie, 31, a general manager for a joinery company, were told by a consultant that she had bowel cancer.

‘I was in a state of shock,’ she says. ‘My brain just stopped functioning.’

She was so stunned she remembers asking just one question: had the cancer spread?

Just days after her 33rd birthday, Katy underwent keyhole surgery to remove the tumour and around a third of her bowel. Fortunately, the disease hadn’t spread into nearby organs.

Four weeks later, she began three rounds of chemotherapy.

‘The side-effects hit me straight away,’ she says. ‘I had extremely bad nausea and really bad ulcers and blisters inside my mouth. And I couldn’t even lift a hand to have a drink.’

She finished treatment in December 2024 and three months later was told she was in remission. ‘It was just like a weight had been lifted,’ she says. ‘Like I’d been reborn.’

Yet Katy had none of the known risk factors – such as smoking, heavy drinking or obesity.

‘I’ve always looked after myself,’ she says.

She was also considerably younger than is typical for this diagnosis – which is most common in people in their 70s and 80s.

As has been widely reported, increasing numbers of younger people are developing bowel cancer despite having few, if any, of the established risk factors.

In the UK, the bowel cancer rate for 25- to 49-year-olds has risen by more than 50 per cent since the early Nineties – and England has the fastest rise in Europe, according to a major international study in The Lancet Oncology in 2024.

Now scientists are launching a major investigation to find out why. The study, called PROSPECT-UK, was launched this month by researchers at King’s College London.

It aims to recruit 250,000 people aged 18 to 50 to gather details about what they eat, how they live and the environmental factors they’re exposed to – as well as analysing blood and stool samples. This will then be compared with their NHS records over the following years.

Four other countries – France, India, Italy and the US – are conducting similar studies as part of an international PROSPECT project.

The fact that people born after the Seventies appear more likely to develop bowel cancer than previous generations at the same age suggests something has changed, say experts.

Katy and her husband, Ollie, were told by a consultant that she had bowel cancer. ‘I was in a state of shock,’ she says. ‘My brain just stopped functioning’

‘The birth-cohort effect is one of our biggest clues,’ explains Andrew Chan, a professor of medicine at Harvard Medical School in the US and co-leader of the international PROSPECT team.

‘Today’s younger generations have grown up with a very different food environment, different patterns of obesity and metabolic disease such as type 2 diabetes, different medication exposures [such as antibiotics, but more on this later] and many other environmental changes,’ he told Good Health.

‘Diet, obesity, antibiotics or environmental exposures may seem like very different possible contributors – but inside the body they may converge on a relatively small number of biological pathways,’ adds Professor Chan.

In other words, together they could be creating a perfect storm that makes cancer more likely at a younger age.

And what appears to be happening is that some young people are effectively ageing faster.

One of the leading suspects for premature ageing is poor metabolic health – particularly obesity and type 2 diabetes, both of which have become more common in younger adults.

Excess body fat, particularly around the internal organs, can cause long-term inflammation and make the body less sensitive to insulin, the hormone that helps control blood sugar.

To compensate, the body produces more insulin, but this hormone also encourages cells to grow.

The concern is that persistently high insulin levels help abnormal cells in the bowel to multiply – while inflammation can damage the cells lining the bowel, forcing the body to replace them more frequently and increasing the risk of mistakes in the DNA, causing cells to become cancerous.

Indeed, scientists working on the international PROSPECT project have already identified a link between accelerated ageing in fat tissue and bowel cancer in younger adults.

‘Two people who are both 40 years old may not be ageing biologically at exactly the same rate,’ explains Professor Chan.

As we age, damage builds up in the DNA of our cells, while the body’s ability to repair that damage or destroy cells that have gone wrong becomes less effective.

If this ageing process begins earlier, abnormal cells may have a better chance of surviving and developing into tumours.

An increasing focus for concern is ultra-processed foods (UPFs), including ready meals, packaged snacks and sugary drinks.

Today, UPFs account for around 60 per cent of the calories eaten in Britain – worryingly, almost two-thirds of the calories British teenagers consume are from ultra-processed foods, reported the European Journal of Nutrition in 2024.

The potential risks were highlighted in research published in JAMA Oncology last November – this found that women aged under 50 who ate the most UPFs had 45 per cent higher odds of having precancerous growths in their bowel than those who ate the least.

This does not necessarily mean that processing itself is causing the disease, says Dr Rosiered Brownson-Smith, a researcher at King’s College London working on PROSPECT-UK.

Andrew Chan, a professor of medicine at Harvard Medical School in the US and co-leader of the international PROSPECT team

People who eat more of these foods may also consume more calories, eat less fibre or put on weight, she explains.

Too little fibre can alter gut bacteria and reduce production of protective substances such as butyrate – an important by-product when gut bacteria break down fibre from vegetables, fruit and wholegrains, it helps keep the bowel lining healthy, reduces inflammation and helps control abnormal cell growth.

A study in Nature Metabolism last year found that butyrate could slow the growth of bowel cancer cells in the lab by changing the activity of genes that control how quickly cells multiply.

Without enough fibre, gut bacteria may instead break down more protein, producing chemicals that can be harmful to the bowel lining, explains Sylvia Zanesco, a nutrition researcher at King’s College London. She is investigating whether eating more fibre can improve changes linked to bowel cancer risk in a 12-week study involving identical twins under 55.

It’s not just that UPFs can lack fibre – scientists are also investigating additives such as emulsifiers, used in foods such as sauces and ice cream to stop ingredients separating.

‘There is growing evidence to suggest that some emulsifiers can affect the gut and promote inflammation,’ says Sylvia Zanesco.

Although she’d always thought she’d eaten reasonably healthily, Katy says she often bought convenience foods such as pizzas, chicken Kievs and soup, and paid little attention to how much fibre she was getting.

She’s changed her diet radically since her diagnosis, checking food labels more carefully.

‘I looked the other day at the back of a jar of soup and there’s a lot of added ingredients in there and so I just make it myself from scratch now,’ she says.

‘The biggest thing that I’ve changed about my diet is my fibre intake,’ she adds – she now aims for 30g a day, eating more nuts, seeds, fruit and vegetables.

And then there is the potential role of antibiotics. Their use rose sharply during the 1980s – prescriptions in England alone increased by 21 per cent from 32.8million in 1980 to 39.8million in 1988, according to UK government figures.

Meanwhile, research involving 73 countries, published in The Lancet Global Health in 2020, found antibiotic use among children under five rose from 36.8 per cent in 2005 to 43.1 per cent in 2017.

By wiping out beneficial as well as bad bacteria, antibiotics can potentially mean harmful organisms may have less competition for food and space, allowing them to multiply.

A study published in the British Journal of Cancer in 2022 found that antibiotic use was linked to a 49 per cent increase in the risk of bowel cancer in the under 50s.

Professor James Kinross, a colorectal surgeon and researcher at Imperial College London, believes disruption to gut bacteria could help explain the rise in bowel cancer in younger people.

He says that when harmful bacteria multiply, they can cause inflammation that damages the bowel lining.

And producing new cells to replace those that have been damaged increases the chances of mistakes occurring when their DNA is copied.

‘In some people, these mutations may sit quietly for years, without doing anything – and in others they may grow quickly,’ he told Good Health.

Scientists have also uncovered evidence that colibactin, which is produced by certain strains of E. coli bacteria, could be damaging bowel cells decades before cancer develops.

Unlike the E. coli associated with food poisoning, strains known as pks-positive E. coli can live harmlessly in the bowel without causing any symptoms.

Around one in five healthy people carries them – babies can acquire them from their mothers around birth.

Although regular physical activity is known to protect against bowel cancer, researchers in the US have been investigating whether repeatedly running marathons and ultramarathons – increasingly popular among younger age groups – might have the opposite effect.

In a study published in Cancer Epidemiology in August this year, doctors examined 94 endurance runners aged between 35 and 50 who had completed at least five marathons or two ultramarathons – they found 15 per cent had advanced adenomas, growths in the bowel that can sometimes develop into cancer.

Dr Timothy Cannon, an associate professor at the University of Virginia School of Medicine, who led the research, believes repeated marathons and ultramarathons could damage the bowel by depriving it of blood and oxygen.

‘This loss of blood flow to the gut may cause recurrent cell death and dysregulated cell division (ie abnormal cells that can lead to cancer),’ he told Good Health.

Why these bacteria contribute to cancer in some people but not others is not fully understood.

But a diet lacking fibre increased inflammation in the bowels of mice, allowing these bacteria to multiply, reported Nature Microbiology last year.

This can then damage the DNA inside bowel cells, including a gene called APC, which normally acts as a brake to stop cells multiplying out of control. If that brake is damaged, abnormal cells may begin to grow.

In a study published in Nature in 2025, scientists analysed 802 bowel cancer tumours from patients and found signs of DNA damage caused by colibactin in around one in five.

Crucially, this damage was 3.3 times more common in patients diagnosed before the age of 40 than in those over 70.

‘One way to think about it is that such an exposure could give some colorectal cells a mutational “headstart”,’ says Professor Ludmil Alexandrov, a cancer researcher at the University of California San Diego, who led the study.

But scientists are also looking beyond our diets and the bacteria in our bowels.

Pesticides are one concern. A study published in Nature Medicine in April found a possible link between bowel cancer in people under 50 and picloram, a weedkiller used in agriculture – when bowel tumours from younger patients were compared with those from people over 70, younger patients were more likely to have chemical changes to their DNA associated with exposure to picloram.

The researchers also found that areas in the US with higher rates of picloram use also tended to have higher rates of bowel cancer among younger adults.

Another concern is PFAS, the so-called forever chemicals used in products such as non-stick cookware, waterproof clothing and some food packaging.

In a study published in Environmental Science & Technology in 2023, researchers at Yale University exposed bowel cancer cells in the lab to two common PFAS chemicals, PFOA and PFOS.

They found that the chemicals made the cancer cells more mobile, a change associated with the ability of tumours to spread.

Earlier research in 2005 found that levels of PFOA in people’s blood more than doubled between 1974 and 1989, raising the possibility that people now developing bowel cancer in their 30s and 40s were exposed to these chemicals from childhood.

Microplastics are also under investigation, with a review published in Cancer Epidemiology last year finding microplastics were present in bowel tumours.

Scientists suspect these particles could irritate the bowel lining, cause inflammation or interfere with the bacteria living there.

The concern is that today’s younger adults have been swallowing these particles since childhood, while their bowels and immune systems were still developing.

And children may be especially vulnerable because they take in more microplastics for their body weight than adults, while their organs, immune systems and ability to break down harmful chemicals are still developing, according to research published in Pediatric Research in July.

For Katy Lander the question of why she developed bowel cancer at 32 remains unanswered.

She has decided not to return to work, preferring to spend more time with her children, now aged eight and five.

But being cancer-free has not removed the fear of the cancer recurring.

‘You live between sort of seizing the day and being back to that place of paranoia,’ she says.

Meanwhile, while researchers investigate the causes, what should we all be doing now to minimise our risk?

‘If I had to prioritise areas right now, I would put metabolic health high on the list of things people should tackle,’ says Professor Chan.