Dr Emily Leeming investigates alarming trend in fit young people developing bowel cancer, how to cut your risk

Why are so many young people developing bowel cancer? It’s a question that scientists around the world are grappling to understand – and those scientists include me.

I’m part of a team at King’s College London who have been awarded a £20million grant to work alongside researchers at Harvard University to explore what could be behind the ­extraordinary surge in cases in people under the age of 50.

It’s not only bowel cancer – cases of ­cancer generally have been rising among the young: Cancer Research UK reports that between 1995 and 2019 rates of all cancer increased by 24 per cent among those aged 25-49, more than twice the rise in the over-75s – the group most at risk of getting cancer.

And bowel cancer rates in the under-50s are expected to increase by more than 140 per cent by 2030, according to a study in the journal JAMA Surgery in 2015. Meanwhile, globally the cases among the over-50s have stabilised.

So what could be driving this rise?

Our international research team – funded by Cancer Research UK and Dame Deborah James’s Bowelbabe Fund – is using multiple approaches, from studies in mice and lab work to clinical interventions, in order to understand the underlying causes.

For although 34 per cent of young bowel cancer cases run in families (double that of older bowel cancer cases), most still don’t have obvious genetic causes, suggesting that environment and lifestyle might be involved.

But while a healthy diet and lifestyle are linked to a lower risk of bowel cancer, there are also anomalies where the super fit, slim and healthy are getting this disease too, including those such as Dame Deborah James, who died two years ago after being diagnosed in 2016 with stage 3 bowel cancer – at only 35 years old.

And there are key differences between early-onset bowel ­cancer and getting it later in life. For example, in young people, bowel cancer more commonly grows on the left-hand-side of the colon and the rectum than it does in later life. It also tends to be more aggressive and more likely to spread.

To try to understand what’s going on, one of the key new areas of bowel cancer research is studying how the gut microbiome – the collection of 100trillion microorganisms that lives in your lower intestine – may be involved.

Studies in animals have, for instance, identified the potential involvement of toxins produced by ‘bad’ gut bacteria in the development of bowel cancer, by triggering an immune cell response or damaging the cells’ DNA.

In humans, multiple studies have now shown there are substantial changes in the amounts of certain gut bacteria in those with bowel cancer, including F. nucleatum, B. fragilis and E. coli.

A study published in the journal Nature this year found that there are similar changes in the gut microbiome in bowel cancer no matter what the age. Scientists have been able to accurately ­predict through ­analysing the make-up of the gut microbiome from stool samples if bowel ­cancer is present.

There are still many unknowns in this field of research, but changing the gut microbiome is a promising potential approach to lowering bowel cancer risk.

So what can you do to reduce your risk, whatever your age?

Stick to tap and boiled water

One new focus in bowel cancer research is microplastics. The main way that microplastics enter our body is through what we eat and drink, disrupting the gut, and harming the mucus ­lining the gut walls.

This mucus layer helps to keep harmful bacteria out – but when it thins, it can potentially allow microplastics to migrate into the gut wall. Indeed, a 2023 study in Environmental Chemistry Letters found there are more microplastics in bowel cancer tumours than in the gut tissues of healthy people.

Separately, a new study in the journal of The Proceedings of the National Academy of Sciences found that bottled water contains nearly ten times more microplastics than previously thought.

While you can’t avoid microplastics completely, bottled water contains 160 times more microplastics than tap water (according to a 2023 review in the journal Science of The Total Environment), so stick to tap water to limit your microplastic intake.

Boiling water for at least five minutes can also lower the microplastic content by up to 80 per cent, as the microplastics get trapped in the limescale formed from calcium in the water. Invest in a non-plastic reusable water bottle for you and your children – and avoid heating food in plastic containers, as this too may help microplastics migrate into your meal. Instead, heat it in a ceramic bowl or plate.

Use processed meat just as flavouring

Most people know by now that processed meats – for example, bacon, salami and ham – which are preserved in some way, for instance by curing, salting or smoking, are a recognised ­carcinogen, strongly linked to bowel cancer (red meats, such as beef, pork and lamb, are also linked, though the evidence is less clear cut).

A 2022 study in the International Journal of Epidemiology found that every 70g of red or processed meat a day – the equivalent of two or three rashers of back bacon – was linked to a 32 per cent greater risk of ­colorectal cancer.

One of the reasons could be down to how the gut microbiome breaks down the iron and preservatives such as nitrates and nitrites found in red and processed meats, leading to the formation of N-nitroso compounds, potent carcinogens.

To cut down on red meat, swap some of it for plant protein – for instance, add lentils to your bolognese sauce. When it comes to processed meat, you don’t have to completely cut it out, but try to limit your intake.

Instead, use it occasionally to flavour veggie dishes, as vegetables contain plenty of beneficial compounds that can neutralise some of the potential harm.

Add onions to (nearly) everything

There’s one food component that’s essential for good gut health, and that’s fibre, the roughage from plant foods such as fruit, vegetables, wholegrains, beans, nuts and seeds.

Fibre keeps your gut lining healthy and sweeps away any built-up waste. Every 10g of fibre you eat a day is linked to a 10 per cent lower risk of bowel cancer, according to a 2011 research review in the BMJ.

One key type of fibre you should try to get enough of is prebiotic fibre. When this is ­fermented by your gut bacteria, it produces short-chain fatty acids that support a healthy gut lining, reduce inflammation and may even protect against bowel cancer.

Onions, garlic, leeks, chickpeas, lentils, asparagus, Jerusalem artichokes and chicory root are all high in prebiotic fibre. Whether you’re making an ­omelette, soup, sauce or stew, try using onion and garlic as a base to ramp up the prebiotic fibre content.

Eat more yoghurt - even the sweet stuff

A study published in the journal Cell, Host & Microbe in 2021 found that six servings of ­fermented foods a day increases gut microbiome diversity (a sign of a healthy gut) and lowers inflammation, a risk factor for bowel cancer.

Don’t feel like you only have to eat buckets of kimchi and ­sauerkraut, there are plenty of other fermented foods, too, such as yoghurt, most cheeses, kefir, tempeh, sourdough, miso and fermented pickles.

Animal studies suggest that beneficial bacteria, such as those found in fermented food, stick to the gut lining, preventing harmful pathogens from doing the same. Even eating yoghurt just once a week is related to a 16 per cent lower risk of bowel cancer than never eating yoghurt, according to a study in The American Journal of Clinical Nutrition in 2021.

A plain, unsweetened yoghurt such as Greek yoghurt is a great choice – though even ultra-­processed, sweetened fruit yoghurt can have a similar ­benefit, according to a 2022 study in the BMJ.

This might seem confusing as we know that eating a lot of ultra-processed foods isn’t good for your health – but not all ultra-processed foods are made equal.

Having said that, ideally choose unsweetened, plain yoghurt.

Swap beer for (a little) wine

Alcohol is harmful to the gut microbiome, and could be a potential factor in the development of bowel disease.

Drinking more than 14 drinks of beer and spirits a week triples the bowel cancer risk, according to a 2003 study in the journal Gut.

Wine is a less harmful choice, possibly because it contains antioxidant compounds, such as anthocyanins and resveratrol, that may positively influence the gut microbiome and have anti-­inflammatory effects.

A better choice is alcohol-free wine, which still contains these beneficial compounds but not the alcohol which irritates the gut. Alcohol-free or low-alcohol beers are also a good alternative.