Bowel cancer endangers many Kiwis - how can people reduce their risk?

Bowel cancer is New Zealand's second most deadly cancer, with one in 10 people now diagnosed under the age of 50.

As the waitlist for colonoscopies grows, people can manage their risk of developing bowel cancer by upping their fibre intake with more plant-based foods, says colorectal surgeon and scientist Dr James Kinross.

"Minimising the amount of ultra-processed foods that you consume and the amount of alcohol that you drink - that's a really important factor in determining your risk of bowel cancer," he tells Saturday Morning.

Investing in and preparing your own meals gives you the control to choose foods that will nurture your gut microbiome, Kinross says.

Reducing the amount of red meat that you eat, if you do eat a lot of it, has well-evidenced benefits, he says, but perhaps a bigger problem is not eating enough vegetables.

The average New Zealander eats around 15 grams of fibre a day, but for the sake of our gut, we really need to eat around 30 grams a day, Kinross says.

"Microbes just love to eat fibre. When they consume fibre, they produce lots of anti-carcinogenic, anti-inflammatory molecules that protect you. So, trying to get enough fibre into the diet is super, super important for gut health."

"It means minimising the amount of ultra-processed foods that you consume and the amount of alcohol that you drink - that's also a really important factor in determining your risk of bowel cancer."

Globally, billions of doses of antibiotics are prescribed every day. Many of those antibiotics are lifesaving and important, Dr Kinross says, but from an evolutionary perspective, their presence has transformed all microbial life systems on the planet.

It's not just a single dose of antibiotics that's the problem, he says, it's the frequency with which people are given antibiotics, delivering "hit after hit after hit" to their gut microbiomes.

"If you're vaccinated, you're much, much less likely to need antibiotics or to need other medicines in the future."

Hygiene is necessary, but we've become a little bit too obsessed with avoiding germs, Dr Kinross says.

Washing your hands after going to the bathroom and before cooking food is wise, he says, but many of us would benefit from getting our hands dirty a bit more by spending time outside and having real-world, physical interactions within our community.

People born in the '90s or the early 2000s have a risk of bowel cancer four times higher than someone born in the 1950s or 1960s, he says. Part of the reason seems to be that younger people have smaller social networks, which leads to them having a less diverse gut microbiome.

"When you kiss someone, you know, you share microbes. A snog is worth about 80 million microbes. But you don't have to kiss, you could just shake hands.

"That real-world interaction that we have with people is really, really important in many aspects of our mental health and many aspects of our health, full stop."

Dr James Kinross will be a guest speaker at next month's 2025 New Zealand Society for Oncology Conference in Dunedin.

Is garlic good for gut health and high blood pressure?

"It's got lots of very well-established health benefits. It's quite good for breaking down biofilms, which are sort of thick gels that microbes form in the gut. Quite good for the gut, good for naturally controlling microbes within the gut."

Can you please talk to us about sugar and its relationship to bowel health?

"We've got really good epidemiological and biological data that when you have too much refined sugar in your diet, it's bad for lots of different forms of health outcomes.

"The problem with sugar is that it's really hard at a societal level, or population level, to try and get people to reduce the amount of sugar, not because people are lazy. It's just that it's so aggressively marketed, and it's enormous. It's in a lot of the ultra-processed foods. Refined sugars are definitely something to try to minimise your intake of."

Well-meaning medical professionals prescribe strong oral antibiotics. Should you try to get through your fever without the antibiotics?

"We need to be careful here. If you've got a fever, and your doctor says, Look, you need to have an antibiotic. You need to take antibiotics as a life-saving medicine.

There are really good reasons to take antibiotics. If you've got a bacterial infection, you need it, but I think sometimes we give out antibiotics unnecessarily. Just because you've got a temperature doesn't necessarily mean that it's a bacteria causing that at that temperature.

"Instead of saying, No, I don't want to take the antibiotic, it means you could say that your doctor, 'Could we make sure we take some culture so that I'm on the right antibiotic to kill that bug, and take the precisely the right course for it?' That's just a simple thing that you can have a conversation with your doctor about."

If you're on antibiotics, and someone suggests taking probiotics is going to help, what do you think?

"Good idea. If you are taking antibiotics, taking a probiotic is a good thing. The few things you need to know if you're taking a probiotic are that if you're going to take one, you need to take one which is high dose. Certainly, more than five to the power of nine colony-forming units. It'll say that on the side of your bottle.

"You need to take [probiotics] for some time. You can't just take a probiotic once or twice and hope it has an effect. That's not how it works, because these are living organisms, and they've got to grow, and "engraft" in the gut. You need to take one, really, from a minimum of six to eight weeks for it to engraft.

"When you're giving a probiotic, they still need to feed and survive in the gut. So, if you're going to the trouble of taking a probiotic because you're taking an antibiotic, also think about your diet. That's a really good time to minimise alcohol, minimise refined sugars, and have a plant-based diet."

Can you turn it all around? Can you change the direction that you're heading in terms of your gut health if you've had a lot of antibiotics as a young person? Can you get better?

"That's such a good question. The answer is yes, but it's not always easy, and we're only just beginning to understand this. There are some studies that show even just one course of very broad effects of antibiotics can have a very long-lasting impact on the gut. You can also make changes by thinking about nutrition, diet and lifestyle.

"Some patients who are really sick, who have significant side effects of antibiotics, have a particular infection called Clostridium difficile. What we have to do is give them a wholesale new community of bugs through something called faecal transplantation. We'll take a faecal sample from a healthy person, and we'll put that into someone who's not very well, and it can be extremely effective at creating a completely new community [of microbes].