The emails, so many of them heartbreaking, have been flooding our inboxes. Mostly they’re from young people – in their 30s or early 40s – who have been diagnosed with bowel cancer. There have been hundreds – and many told stories that were strikingly similar.

They’d ignored their symptoms – blood in their stools, weight loss or stomach pain – or, worse, had them dismissed by GPs because they were ‘too young’ to have this awful disease. Other emails came from grieving parents who’d watched their children die from bowel cancer after a diagnosis came too late.

But what they all had in common was a need for an answer – to understand why this cruel disease, which is overwhelmingly diagnosed in the elderly, has started affecting an increasing number of young, fit and otherwise healthy adults. The statistics are stark: cases of bowel cancer are rising twice as fast in the under-50s compared with older adults – and not just in the UK, but around the world.

It’s a puzzling conundrum that has prompted us, as leading scientists in nutrition and the epidemiology of disease at King’s College London, to take action.

Earlier this year it was announced we would lead the UK-arm of a £20 million research project called PROSPECT that will analyse data from millions of people to hunt for the factors driving this surge in colorectal cancers.

It was this announcement that prompted the emails – validation that this is a hugely important issue that must be addressed.

Our five-year study, funded by Cancer Research UK and the Bowelbabe Fund set up by campaigner Dame Deborah James before she died of bowel cancer aged 40 in 2022, will involve an international team of about 100 scientists. All are experts in their field, be it genetics, cancer, diet or molecular biology. Our research will focus on the role of the microbiome – the community of trillions of bacteria that live in the gut – and its connection to colorectal cancer.

It’s thought that if certain bacteria are present in the microbiome, you may be more likely to develop the disease. If we can firm this up, it’s possible that, at some point, doctors could work out from a stool sample whether you might be more at risk of tumours later on.

We also plan to run clinical trials to see whether a simple change in diet could improve your microbiome and reduce your risk – and even whether giving younger adults the weight-loss jabs such as Ozempic and Wegovy might help.

We don’t have the answers yet, but within five years we might have some. It could be game-changing.

What we do know is that while the prevalence of many cancers has plateaued over recent years, cancers in younger people are bucking that trend.

Strictly dancer Amy Dowden was diagnosed with stage-3 breast cancer aged 32 last year. And just last week, actor James Van Der Beek – who appeared in the 90s TV show Dawson’s Creek – revealed he’d been diagnosed with bowel cancer, aged 47.

In three decades, the incidence of this kind of cancer has rocketed by 80 per cent worldwide. Those born in 1990 – who are in their mid-30s today – are nearly two and a half times more likely to get bowel cancer than someone born in 1950.

One 45-year-old woman who emailed us, who was recently diagnosed with the disease, said two of her classmates from school also have it.

Numbers of young adults aged 20 and over being diagnosed started to rise in 1993. Whatever this cohort has been exposed to, it began in the 1970s. This gives us clues about what might be causing it. For example, it was around then that we started to see huge changes in our food landscape. Ready meals became popular, and fast-food outlets began appearing on our high streets.

Our lives have also become much more sedentary, and rates of obesity – known to drive many types of cancer – have soared.

But figuring out precisely what the issue is remains a million-piece jigsaw. Many people diagnosed with bowel cancer are a healthy weight and don’t eat a diet many would consider unhealthy. To start to unpick these issues, we need to look at the lives of millions of people to tease out what those who develop these cancers early have in common.

Fortunately we have some huge studies we can use. We have our own Zoe database, which began as the Covid Symptom Study app to track the spread of the virus.

It includes the microbiome data from our members, making it the largest microbiome database in the world. It now has 200,000 people recruited into a separate arm called ZOEPREDICT, which carries out nutritional research and has huge amounts of information about what people eat and how they live their lives.

Another, the Nurses’ Health Study, has data on 280,000 people recruited since 1976.

We’ll look at which foods might cause or prevent the disease. Among older people, processed meats are a factor – eating the equivalent of three slices of sandwich ham a day increases the risk by 32 per cent. But there might be different risks for younger people, and potentially more of a role for ultra-processed foods – packaged foods that contain a lot of chemical additives.

No food is intrinsically ‘bad’, so we’ll also look at dose to see whether we can work out that if a food does increase the risk, how much is too much. There’s already good evidence, for example, that those who consume two sugary drinks a day are twice as likely to develop bowel cancer as those who have only one a week.

These studies also allow us to look at the impact of other possible risk factors, including environmental pollutants such as traffic fumes, work-related chemicals, plastics and smoke from fires or woodburners, and also things such as antibiotic use, which can affect the gut.

One of the other exciting elements is whether anti-obesity drugs can play a role. These mimic the release of the body’s ‘hunger hormone’, GLP-1, which tricks the brain into thinking the stomach is full.

We already know obesity can cause colorectal cancer. But there is some early evidence these drugs might have a separate effect on cancer risk by reducing inflammation, improving metabolic function and altering the microbiome. While it’s hard to unpick what might be causing this, a clinical trial of 40 people, led by Harvard gastroenterologist Professor Andrew Chan, who is one of our collaborators, will test it out.

Those recruited will already have an increased risk of the disease because they have had polyps removed – tiny growths in the colon which can lead to cancer in around five to ten per cent of cases.

They must also qualify for the jabs because they’re already obese or have type-2 diabetes. Half of them will get the jabs, while the other half will get standard advice to lose weight, and they’ll be tracked to see how many develop cancerous cells.

Obviously we don’t yet know whether young people identified at risk of early-onset colorectal cancer could, in future, be given drugs such as Ozempic.

Just last week it emerged that a woman had died after taking similar weight-loss jab Mounjaro – the first confirmed UK death linked to the drugs. It’s certainly unlikely that these drugs will be a magic bullet, and they won’t be able to offset what is a much larger problem.

We have a broken food landscape in this country, we’re exposed to terrible diets and pollutants that all work in some way to increase the risk – and to increase it far earlier in life than was previously the case.

Data suggest the risk is growing with each generation, which is why we must act quickly.

Hopefully we can not only reduce the trend, but reverse it – and finally get some answers for those affected by this terrible disease.

Shelby was hit by bowel cancer at 24... what could have caused it in such a young and healthy woman? 

Shelby Preston had only recently turned 24 when she was diagnosed with bowel cancer in July 2022.

She went to see her GP numerous times from the age of 18 with symptoms including stomach pain and spasms, and blood when she went to the toilet.

Slim and healthy, she lost weight despite eating normally and, at her lowest, ended up at just six and a half stone.

She was told she was too young for it to be anything sinister, and was referred for further investigations only after begging for help because of the volume of blood she was passing.

To the doctors’ surprise, tests uncovered a bowel tumour, which was removed in November 2022. Fortunately it was caught at an early stage and, although she needed a temporary stoma, she did not need radiotherapy or chemo.

‘It was a really stressful time and the doctors seemed so shocked it was cancer,’ says the ambassador for charity Bowel Cancer UK, from Preston. ‘I’m proof that doctors shouldn’t dismiss these symptoms in young people – if I’d believed them, that it was something simple like piles or irritable bowel syndrome, I could be in a much more serious situation now.

‘The impact of bowel cancer is significant in younger people – I had to freeze my eggs before surgery in case I needed chemotherapy and it affected my fertility. There was a chance I’d be left with a permanent stoma. And, of course, I’ll always worry it could come back.

‘I have no history of bowel cancer in my family, and I was healthy and reasonably fit. I’d walk all the time and I ate relatively healthily.

‘It’s so important scientists work out what’s driving cases like mine.’