Colon cancer is rising in people under 50. James Kinross, a gastrointestinal surgeon who researches how the gut microbiome affects our risk of the disease, told Business Insider that poor gut health could be partly to blame.

Research suggests the gut microbiome, the trillions of microbes that live in the digestive tract, has a wide-ranging effect on our health. But sterile, urbanized lifestyles appear to have made them less diverse overall and, therefore, weaker, said Kinross, who's based at Imperial College London.

"You're seeing a generational loss in our internal ecology, which is being hammered with a series of environmental hits that it simply cannot adapt to," he said, referring to factors including microplastics, ultra-processed foods, and minimal access to nature. Many studies have linked these changes in the gut microbiome to an increase in colon cancer risk.

But, the gut microbiome is changeable, meaning there are things we can do to increase its diversity, which in turn could help lower colon cancer risk. "It is an ecosystem which you can adapt, and you can modify," Kinross said.

Kinross previously shared with BI how he eats to boost his gut microbiome. He also shared the three things he does aside from healthy eating to lower his colon cancer risk.

Don't take antibiotics if you don't need to

Kinross limits his antibiotic use where possible because the medication disrupts the gut microbiome. Trevor Williams/Getty Images

As a surgeon, Kinross is acutely aware that antibiotics are often necessary and save millions of lives each year, but he believes we use them too liberally — particularly to treat viral infections they can't tackle.

"In my house, to qualify for antibiotics, you've really got to have a pathogen that you need treated," Kinross said.

Kinross and his family limit their use of antibiotics as much as possible because taking them can disrupt the ecosystem of the gut microbiome, killing off good bacteria along with pathogens and reducing diversity.

He likened it to pouring weed killer all over your garden. "Your garden won't really grow into a lovely garden full of wild meadows and flowers and color. It will just be brown and lifeless," he said.

Take vitamin D

Kinross takes a vitamin D supplement because evidence suggests that having enough of the nutrient is important for gut health.

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Vitamin D is crucial for several biological processes, including calcium absorption and cellular repair, but it also keeps the lining of the small intestine strong. If the lining becomes weak, microbes can pass through it into the bloodstream and cause inflammation. Chronic inflammation is linked to a higher risk of chronic diseases, including cancer.

Vitamin D is found in foods including oily fish, egg yolks, and red meat, as well as from sunlight. In countries with climates like the UK's, where Kinross lives, it can be difficult to get enough vitamin D in the colder months, and residents are advised to supplement from October to March.

Socialize

Social connections are a pillar of health. pixdeluxe/Getty Images

Kinross goes cycling with friends regularly and makes sure to sit down to eat dinner with his family in the evenings. As well as being a pillar of overall health, research suggests that socializing positively impacts the composition of our gut microbiomes, Kinross said.

We exchange microbes through physical touch, and studies have found that friends, family members, and spouses have similar gut microbes to one another.

A 2024 study published in the journal Nature, based on 1,787 adults from 18 isolated villages in Honduras, found that people in the same social network shared more similarities in their gut microbiomes compared with those outside it. This was regardless of diet, water sources, and medications. Spouses and people living together had the highest amount of microbial sharing, but the phenomenon still occurred among friends and even friends of friends.

"Our social interactions, our real-world social interactions, define so much of our health," Kinross said. "It's good for all aspects of our health. It's good for our mental health, it's good for our cardiovascular health. It's good for everything. But if you're not having real-world social interaction, you are not really optimizing your gut health, I believe."