Bowel cancer is now the leading cancer killer of men under 50 in the UK. If you were born in the 1990s, you’re 4 to 5 times more likely to develop it than someone born in the 1960s. For decades, nobody could explain why. The usual suspects (obesity, alcohol, red meat) didn’t account for the scale of the rise, and they definitely didn’t explain why younger people with none of those risk factors were turning up with stage 3 disease.
Then the research started to catch up. A 2024 systematic review in a major oncology journal identified 4 bacterial species consistently associated with colorectal cancer tumours across dozens of studies. 3 of the 4 come from your mouth. That finding reframes the whole conversation.
The Oral Gut Axis
Your mouth and your gut aren’t separate systems. Everything you swallow, bacteria included, ends up in your gut. In a healthy mouth with healthy gums, that transit doesn’t matter, because the bacteria that live well in your mouth don’t thrive in the colon’s environment, and your immune system clears them.
In a mouth with chronic low grade inflammation (gum disease, poor hygiene, enamel damage), the oral microbiome shifts. Species like Fusobacterium nucleatum bloom. You swallow them continuously. If your gut microbiome is depleted, with low diversity, few short chain fatty acid producers and chronic inflammation of its own, those oral bacteria get a foothold in the colon. They don’t belong there. They drive the kind of chronic, low grade inflammation that over 10 to 20 years sets up the environment for malignancy.
That’s the mechanism. It works slowly, and you feel nothing while it’s happening.
Why It’s Getting Worse in Young People
3 things, in combination.
First, oral health has declined. Modern diets are more acidic, more sugar dense, and higher in ultra processed food than any previous generation’s. Enamel erosion is up. Gum disease rates in under 40s have risen significantly in the last 2 decades. The dental data is clear even where the oncological data is new.
Second, gut microbiome diversity has collapsed. The average British adult eats around 10 to 15 different plant foods per week. The research shows real benefit from eating 30 or more. Ultra processed foods, now 55% of the average UK diet, strip out the fibre and plant polyphenols that feed a diverse microbiome. Emulsifiers used as additives in processed food have been shown in animal models to directly damage the gut lining.
Third, antibiotic exposure. Medical prescriptions matter, and so do the antibiotics in the food chain, in meat and in milk, which add up over decades. A gut microbiome that’s been repeatedly knocked back doesn’t rebuild to the same diversity it had before.
Put those 3 together (a mouth full of inflammatory bacteria, a gut that’s lost its defensive diversity, and a lifetime of low grade antibiotic exposure) and you have the exact conditions the 2024 research describes.
What To Do About It
The oncological argument runs on a 20 to 30 year timeline, which means the prevention conversation has to run on the same timeline. Nobody protects themselves from colorectal cancer in 6 weeks. But you can start now.
On the oral side, the 5 changes that matter: brush twice a day with fluoride free toothpaste if you can tolerate it (hydroxyapatite works just as well); floss daily, not weekly; stop using antibacterial mouthwash, because it’s chemically identical to swallowing antibiotics every morning, and it strips the oral microbiome of beneficial species too; see a hygienist every 6 months, not once a year; and if your gums bleed when you floss, that’s chronic inflammation, not normal.
On the gut side, the 4 changes that matter: eat 30 or more different plant foods per week (herbs, spices, nuts, seeds, legumes all count); add a daily fermented food such as kefir, kimchi, sauerkraut, or a proper L. reuteri yogurt; stop eating ultra processed food in volume (I’m not asking for sainthood, I’m asking you to make it the exception rather than the rule); and only take antibiotics when they’re clinically necessary.
You don’t need to be a BTX client to run that protocol, but most people never hear it from their GP.
At BTX, alongside personal training in Hampstead, we work 1-to-1 with clients on personalised gut and metabolic protocols, with microbiome testing, blood work with Dr Matt Milner (A&E consultant), and nutrition built around your biology. Book at bodytransformationlondon.com, or DM “STRONG” on Instagram @jamescooperbtx.