Why poor gut health could increase your cancer risk – and how to fix it

Cancer cases in the under-50s are rising, and experts believe it may be linked to their gut health. Here’s how to fix it

If your go-to dinner comes via a food delivery app or ready meal, it could be time for a rethink. 
An oncologist in North Carolina believes that the startling rise in cancer cases in the under 50s is down to an over-reliance on fast food among younger generations who tend to ‘grab and go’.
Dr Nicholas DeVito, an oncologist at Duke University, says that all his younger patients have such a diet, and it alters the gut microbiome, making us vulnerable to cancer. 
“While the rates of some types of cancer are declining, several gastrointestinal cancers are on the rise among people under age 50,” notes Dr DeVito. “Even more worrisome: particularly in bile duct and stomach cancer, the rate increases with each younger generation. Ultra-processed food, including prepared meals, packaged snacks, fizzy drinks, cereals, and a host of other items, has emerged as a potential cause for gastrointestinal cancers,” he wrote in Stat news. 
He’s far from the first cancer expert to raise the alarm. A number of studies have found that consuming high amounts of ultra-processed foods (UPFs) such as fast food, flavoured crisps and sugar-sweetened drinks is linked with an increased risk of many types of cancer, including colorectal, breast and pancreatic cancers. UPFs are associated with more than 30 health conditions, including obesity, which also substantially raises the risk of cancer. In fact, a recent study by researchers at the University of Milan found that obesity is contributing to rising UK death rates from bowel cancer among people aged 25-49 years.
There are two possible ways in which UPFs can directly affect the microbiome. “The first is that the actual chemicals in these foods may be damaging to the species of bacteria, viruses, fungi and other microbes that live in the microbiome, reducing the diversity, so that the flora can not thrive,” says Dr Frankie Jackson-Spence, a doctor and clinical research fellow in oncology, who says more robust evidence is needed in this area.
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But what’s more likely is that if you are eating a diet high in UPFs, your diet probably lacks the variety you need. “We know from studies that eating 30 different types of plants a week is optimal for supporting gut microbiome diversity and health. If you eat a ready-made lasagne from the supermarket, it probably doesn’t have the same plant and fibre content as home-made, so you’re missing some of the key nutrients,” adds Dr Jackson-Spence.
Although cancer is generally accepted as a disease caused by genetic characteristics and environmental factors, recent findings have shown that the gut microbiome and its metabolites could account for approximately 20 per cent of cancers.
And our diet has a large part to play in this, especially if we rely on UPFs – crisps, snacks and fast foods that are of virtually zero nutritional value. “If you look at some of the products in the supermarket, they’re filled with chemicals that make them last a year on the shelf – fine if it’s an occasional treat for taste or convenience, but not if we rely on them day in and day out,” says Dr Jackson-Spence. 
One of the theories that explains the role of the gut in cancer risk involves the connection with our immune system. “A large proportion of our immune cells live in the gut – about 70 per cent. So if the microbiome is not in its most optimal state and is not being fed with all of the different kinds of [good] chemicals from plants, then it’s likely our immune system is not functioning in its most optimal state which is a risk factor for cancer,” says Dr Jackson-Spence. 
Poor gut health can also lead to increased inflammation and an imbalance in the gut microbes, known as dysbiosis. “If you don’t have a healthy gut microbiome, the gut lining essentially isn’t functioning optimally and so it may be more susceptible to irritation from external pathogens – inflammation is just your immune system kicking in.” And that can make it vulnerable.
But cancer risk is also connected to lifestyle. If you look at a person who eats a diet high in UPFs – and the average person in the UK consumes over 50 per cent of their diet from them – they usually engage in other less healthy behaviours. “You’re more likely to be obese, which we also know is a risk factor for cancer,” says Dr Jackson-Spence.
Other lifestyle factors such as smoking and drinking alcohol, not getting enough exercise, leading a stressful life and not getting enough sleep have all been linked to a higher risk of cancer. “With cancer, it’s a multifactorial process, with the genetics and the lifestyle of someone who’s consuming a lot of UPFs, as well as the direct effect of the UPF food ingredients themselves,” Dr Jackson-Spence adds.
A lot of food is processed and that doesn’t automatically make it harmful. The foods that we should cut back on are UPFs, those that are of low nutritional value or contain ingredients that are harmful to our health when eaten in excess.
“In people who consume more processed red meat – bacon, salami, sausages – and ultra-processed food, there is an increased risk of colon cancer,” says Gabrielle Morse, a specialist dietitian from The Gut Health Doctor, who also says alcohol is also best avoided. 
Linked to 30 different types of cancer, alcohol is linked to the toxic metabolites that are created when your body breaks down alcohol, releasing those toxins into the bloodstream. Alcohol also causes a change in gut integrity, potentially causing increased inflammatory responses and spread of pathogens to intestinal tissues.
Another red flag ingredient, emulsifiers are found in multiple UPFs, used to prolong the shelf life of foods. Research suggests they can harm the delicate balance of the gut microbiome, leading to chronic inflammation and increasing cancer risk. Emulsifiers are found in all kinds of foods including condiments, cereal, biscuits and pre-packaged supermarket cake. 
“While research shows that having too many emulsifiers and additives in our diet is linked to increases in bowel cancer and inflammatory bowel disease, we still don’t really know which ones and in what quantity,” says Morse. “The most protective advice is to focus more on eating whole foods and cooking everything you can from scratch, where possible. Rather than opening a packet of biscuits or crisps for a snack, go for nuts and a banana”. 
Morse says there’s a grey area over how much UPF we can safely consume, but by increasing our intake of healthy whole foods, we’re protecting our gut. For better gut health she recommends having 30 plant-based foods a week rather than eating the same few foods on repeat. “If you only ever have, say, carrots, broccoli and apples, that’s not really enough. Vary it more so you’re having all the superfoods across the week, and pulses such as lentils and chickpeas every single day, because we know they are so protective for bowel cancer. And make sure you have a lot of omega-3s such as salmon, mackerel, sardines and nuts which are anti- inflammatory and reduce bowel cancer risk as well as irritable bowel disease.”
And finally, make sure you include plenty of fibre – wholegrains, nuts and crunchy vegetables – which your gut bacteria ferments. “This produces really beneficial short chain fatty acids which protect the lining of the colon, so it’s less vulnerable to cancer development, unlike UPFs which are not feeding the good bacteria and are pro-inflammatory, so they just make the area more vulnerable to cancer,” explains Morse.
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