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Why do so many young people develop colon cancer? It’s a question that scientists around the world are trying to understand, and I include myself among them.
I am part of a team at King’s College London that has received a £20m grant to work alongside researchers at Harvard University to explore what might be behind the extraordinary rise in cases in people under 50.
It’s not just bowel cancer: cancer cases in general have been increasing among young people: Cancer Research UK reports that between 1995 and 2019 rates of all cancers rose by 24 per cent among people aged 25 to 49, more than double the increase in the over-75s, the group most at risk of cancer.
And bowel cancer rates in those under 50 are expected to rise by more than 140 percent by 2030, according to a study published in the journal JAMA Surgery in 2015. Meanwhile, globally, cases among those over 50 have plateaued.
What could be driving this increase?
Dame Deborah James, also known as Bowelbabe, died of bowel cancer in June 2022.
Our international research team, funded by Cancer Research UK and Dame Deborah James’ Bowelbabe Fund, is using multiple approaches, from mouse studies and laboratory work to clinical interventions, to understand the underlying causes.
Although 34 per cent of bowel cancer cases in young people run in families (twice as many as bowel cancer cases in older people), most still have no obvious genetic causes, suggesting that environment and lifestyle could be involved.
But while a healthy diet and lifestyle are linked to a lower risk of bowel cancer, there are also anomalies where super-fit, slim and healthy people also suffer from the disease – including those like Dame Deborah James, who died two years ago after being diagnosed in 2016 with stage 3 bowel cancer, aged just 35.
There are key differences between bowel cancer that appears at an early stage and that which appears later in life. For example, in young people, bowel cancer more often grows on the left side of the colon and rectum than in later life. It also tends to be more aggressive and more likely to spread.
To try to understand what is happening, one of the key new areas of research into bowel cancer is studying how the gut microbiome (the set of 100 trillion microorganisms that live in the lower intestine) may be involved.
Animal studies have identified, for example, the possible involvement of toxins produced by “bad” intestinal bacteria in the development of intestinal cancer, by triggering a response from immune cells or damaging the DNA of cells.
In humans, several studies have shown that there are substantial changes in the amounts of certain gut bacteria in people 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 regardless of age. By analysing the composition of the gut microbiome from stool samples, scientists have been able to accurately predict whether 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 reducing the risk of bowel cancer.
So what can you do to reduce your risk, regardless of your age?
Stick to tap and boiled water
A new focus in bowel cancer research is microplastics. The main way microplastics enter our bodies is through what we eat and drink, disrupting the gut and damaging the mucus that lines the intestinal walls.
This mucus layer helps keep harmful bacteria at bay, but when it becomes thinner, it can allow microplastics to migrate into the gut wall. In fact, a 2023 study published in Environmental Chemistry Letters found that there are more microplastics in bowel cancer tumors than in the gut tissues of healthy people.
Meanwhile, a new study published in the journal 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 drinking tap water to limit your microplastic intake.
Dietitian and microbiome scientist Dr Emily Leeming is part of a £20m project investigating the cause of the growing trend
Boiling water for at least five minutes can also reduce microplastic content by up to 80 percent, as microplastics are trapped in the lime formed from calcium in the water. Invest in a reusable, non-plastic water bottle for yourself and your children, and avoid heating food in plastic containers, as this can also help microplastics migrate into your food. Instead, heat it in a ceramic bowl or plate.
Use processed meat only as a flavoring.
Most people already know that processed meats (e.g. bacon, salami and ham) that are preserved in some way, such as 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, although the evidence is less clear).
A 2022 study published in the International Journal of Epidemiology found that every 70g of red or processed meat per day (the equivalent of two to three rashers of bacon) was linked to a 32% higher risk of colorectal cancer.
One reason could be the way the gut microbiome breaks down iron and preservatives such as nitrates and nitrites present in red and processed meats, leading to the formation of N-nitroso compounds, potent carcinogens.
To reduce red meat consumption, replace it with vegetable proteins (for example, add lentils to bolognese sauce). As for processed meat, you don’t need to cut it out completely, but try to limit your intake.
Instead, use it occasionally to flavor vegetarian dishes, as vegetables contain many beneficial compounds that can neutralize some of the potential harm.
Add onions to (almost) everything
There is one dietary component that is essential for good intestinal health and that is fiber, the forage that comes from plant foods such as fruits, vegetables, whole grains, legumes, nuts and seeds.
Fiber keeps your gut lining healthy and removes built-up waste. Every 10g of fiber you eat a day is linked to a 10 percent lower risk of bowel cancer, according to a 2011 research review in the BMJ.
One key type of fiber you should aim to get enough of is prebiotic fiber. When fermented by gut bacteria, it produces short-chain fatty acids that support gut lining health, reduce inflammation, and may even protect against bowel cancer.
Onions, garlic, leeks, chickpeas, lentils, asparagus, Jerusalem artichokes, and chicory root are all foods rich in prebiotic fiber. Whether you’re making an omelet, soup, sauce, or stew, try using onions and garlic as a base to boost the prebiotic fiber content.
Eat more yogurt, even the sweet ones
A study published in the journal Cell, Host & Microbe in 2021 found that six servings of fermented foods a day increased gut microbiome diversity (a sign of a healthy gut) and reduced inflammation, a risk factor for bowel cancer.
Don’t think you only have to eat buckets of kimchi and sauerkraut, there are plenty of other fermented foods too, including yogurt, most cheeses, kefir, tempeh, sourdough, miso, and fermented pickles.
Animal studies suggest that beneficial bacteria, like those found in fermented foods, stick to the gut lining, preventing harmful pathogens from doing the same. Even eating yogurt just once a week is linked to a 16% lower risk of bowel cancer than not eating yogurt at all, according to a study published in The American Journal of Clinical Nutrition in 2021.
An unsweetened plain yogurt, such as Greek yogurt, is a great option, although even ultra-processed, sweetened fruit yogurt may have a similar benefit, according to a 2022 study published in the BMJ.
This may seem confusing, since we know that eating a lot of ultra-processed foods is not good for our health, but not all ultra-processed foods are created equal.
That said, it is best to choose plain, unsweetened yogurt.
Swap beer for (some) wine
Alcohol is harmful to the gut microbiome and could be a potential factor in the development of intestinal diseases.
Drinking more than 14 drinks of beer and spirits a week triples the risk of bowel cancer, according to a 2003 study published in the journal Gut.
Wine is a less harmful option, possibly because it contains antioxidant compounds, such as anthocyanins and resveratrol, which can positively influence the gut microbiome and have anti-inflammatory effects.
A better option is non-alcoholic wine, which still contains these beneficial compounds but not the gut-irritating alcohol. Non-alcoholic or low-alcohol beers are also a good alternative.
Even people in their twenties need to know the warning signs of bowel cancer.
For more information, visit nhs.uk/conditions/bowelcancer/symptoms.
- DR EMILY LEEMING is a dietitian and microbiome scientist at King’s College London and the author of Genius Gut: The Life-Changing Science Of Eating For Your Second Brain, out now.
