ZOE Science & Nutrition - Recap: How to combat colon cancer | Dr. Andy Chan

Episode Date: May 27, 2025

Today, we’re diving into an important and growing health concern: colon cancer. Recent studies show that cases of colon cancer are becoming increasingly common in younger adults. In fact, the rate has doubled among people under 50 since the 1990s, prompting doctors to lower the recommended age for screening. So what can we do to protect ourselves and our loved ones? I’m joined by Harvard Medical School professor, Dr. Andy Chan, to talk about the importance of colon cancer screenings and how changes to our diet could help reduce the risk of this disease. 🥑 Make smarter food choices. Become a member a zoe.com - 10% off with code PODCAST 🌱 Try our new plant based wholefood supplement - Daily30+ *Naturally high in copper which contributes to normal energy yielding metabolism and the normal function of the immune system 📚 Books from our ZOE Scientists:The Food For Life Cookbook by Prof. Tim Spector Food For Life by Prof. Tim Spector Every Body Should Know This by Dr Federica Amati Free resources from ZOE: Live Healthier: Top 10 Tips From ZOE Science & Nutrition  Gut Guide - for a healthier microbiome in weeks Have feedback or a topic you'd like us to cover? Let us know here Listen to the full episode here

Hello and welcome to Zoë Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're diving into an important and growing health concern, colon cancer. Recent studies show that cases of colon cancer are becoming increasingly common in younger adults. In fact, the rate has doubled among people under 50 since the 1990s, prompting doctors to lower the recommended age for screening.

So what can we do to protect ourselves and our loved ones? I'm joined by Harvard Medical School professor Dr. Andy Chan to talk about the importance of colon cancer screenings and how changes to our diet could help reduce the risk of this disease. In the US, the American Cancer Society just came out with a very sobering report that statistics are such that now the leading cause of cancer death in people younger than 50

among men is colon cancer. The leading cause of cancer death for men under 50 is now colon cancer. And by 2030, they estimate that it will become the leading cause of cancer death for both men and women. So that's a real change from where we were, you know, 10, 20 years ago. And I feel like that is a long way from the common conception, you know, because you're actually saying that as a cause of death, for example, that would actually be higher than breast cancer for women under 50 in just a few years. Is that correct? Did I understand that? Exactly, yeah.

Which I feel is, and is obviously in no way reduces the seriousness of breast cancer or any other cancer, but it does suggest that there is not a popular understanding of just how common this is becoming as a cancer for younger people. Correct, yeah. I mean, I think that's another trend that we're seeing. We're also seeing that, for example,

breast cancer incidence is rising also in younger women, not quite the rate of increase as we're seeing with colon cancer. So cancers in general seem to be shifting downward in terms of the age at which they're starting to first present. But the increases are the most striking for cancer to the gastrointestinal tract. By far the most frequently asked question, interestingly, was about

screening. So could you maybe start with that? Who should be getting screenings? How often? And I know that what actually happens is different country by country. But just looking at this to start with as a researcher and expert, what would be your advice? So as you did mention, things vary from country to country. So I'll speak to this from the standpoint of being a physician in the US. So screening is something that we know saves lives. It's recommended by multiple expert bodies here in the US as well as internationally.

That colon cancer screening is important because most colon cancers in early stages are not symptomatic. So you can't wait for people to get symptoms to diagnose cancer in an early stage. And we also know that diagnosing on an early stage is the critical factor in terms of whether someone can be cured of their disease. So someone who, for example, is diagnosed with stage one or early stage colon cancer, or even if they have very large polyps, those people can be cured of cancer over 90, 95% of the time

through surgery and surgery alone. So 90 to 95% of the time you can actually cure this cancer. I just want to make sure I heard that right. Exactly. It's the most positive thing you've said all episode, Andy. So that's why we put such a strong emphasis on screening is because we can use screening as a way to detect cancer early before symptoms develop and when it's treatable. And ultimately, screening has been shown to reduce death from colon cancer in the long

term. Ten years ago, we only recommended screening for people over the age of 50. But in recognition of this trend toward younger people getting colon cancer, over the last couple years, the screening age has now shifted such that we recommend screening for anybody over the age of 45. That's for people in the general population. Now if you have a family history of colon cancer, then we recommend you start screening earlier, either at the age of 40 or 10 years

before your relative got colon cancer. And that's been something that I think has been the reason why we're seeing the declining incidence of colon cancer in older people. It's because of these screening programs that have been really pushed across the board in the US. And how does it work, Andy? What do you need to do to be screened for this disease?

So screening for colon cancer can take a number of approaches. I sort of divide it up into two categories of screening. One category of screening is what we call invasive screening, or what we do in the US, which is a colonoscopy. So by invasive, it means coming in for a medical test in which you have to drink a laxative to clear out your bowel. You come in the next day and you get some sedatives and you undergo what's called a colonoscopy, which is where a physician like myself passes a small flexible camera through your rectum into your colon

to look for polyps and cancer. It's something that allows us to both look for cancers and look for polyps but also remove them if we see them during the exam and take them out to try to prevent them from developing into cancers. The other form of screening is what we call non-invasive screening. These are tests which don't require you to come in to see a doctor, don't require you to get sedatives or undergo any procedure. And these are tests in which we basically take a small sample of your bowel movement and either look for blood or look for some you know mutations DNA mutations in your bowel

movements. Those screening tests are done in the comfort of your home and you and you send them into the doctor to read and if you see anything abnormal on those tests then you may be referred for that colonoscopy I mentioned with a doctor. And both are reasonable options for screening. Got it. So there is actually the second one where basically you're just getting a sort of sample of your poop and testing it actually is quite effective in terms of picking up these earlier

stage cancers. Yes. So the screening that you can do with just a bowel movement will pick up cancers at a very high rate. It's not as good at picking up polyps. Again, polyps, as I mentioned, is that sort of early tumor. It's not yet a cancer, but it can become a cancer. Those polyps are kind of even earlier in the process of colon tissue becoming cancer.

If you see a polyp and find a polyp, you take it out because you want to interrupt that progression to a cancer. The stool tests are not very good at picking up polyps. The colonoscopies are definitely better at picking up polyps, which is why some people feel more comfortable having the more invasive test, the colonoscopy, whereas other people are more comfortable having the non-invasive stool-based test. And again, depending on the country, you know, you may be restricted in terms of what you have access to. So, for example, in the UK, stool-based testing is what's recommended.

Colonoscopies are reserved really for people who have positive stool-based screening tests. In other words, a screening test that's abnormal or have other symptoms or risk factors that require them to have the colonoscopy. So I would say that a lot of people, particularly young people, should not be afraid to get screened. I think if you're thinking screenings that are very involved kind of invasive tests, it doesn't have to be. The stool-based tests are really quite good and really what we feel in the

field is that the best screening test and the best way to prevent cancer is the one that you can do, the one that gets done. And so if you can submit a little sample of poop and that's all you need to do, I think that that goes a long way toward prevention. Can I talk about how you could change your diet in order to reduce your risk of colon cancer? Yes. So we'll start with what we know and then we'll start with where we hope to go. So what we know is that red meat intake and processed meat is a risk factor for colon cancer. So the International Agency for Cancer Research did a very comprehensive review of dietary risk factor for colon cancer. So the International Agency for Cancer Research did a very comprehensive review of dietary risk factors

for colon cancer, and they felt the most compelling evidence was for red and processed meat as being a risk factor. So reducing your intake of red and processed meat as much as possible is one key way that you can reduce your cancer risk. The other factor I think also that's becoming increasingly important is alcohol. I think trying to reduce alcohol intake is probably important to do. It's not clear whether there is a threshold effect. I think that it's becoming maybe more clear that it's probably a linear risk factor. So the less you drink, the better in terms of your risk for developing colon cancer.

I wanted to ask you about that because I know that on an overall basis, it isn't just like the more you drink, the worse. I've understood from a lot of scientists here and talking about the Vita Zoe that's sort of like one glass of red wine probably isn't making things any worse at all, but then it gets much worse as you increase. But in this case, you're saying it's not like that. Even just any amount of alcohol is increasing the risk and it just sort of goes up and up as you drink more. Yeah, I think it's not clear. I think that how steep that curve is. So, you know, it could very well be that, you know, there's a little bit of an increase in risk with that one glass

of red wine, but as you start to get up to two, three drinks, you start to really get steep increase in risk. That sort of dose response, if you will, I think is still something that we're grappling with. Got it. Okay, so not clear. So it might be that it's not completely the same, but it's certainly not the all clear that some people might want it to be who would like to be able to have a glass of wine. Right, right. So those are the established risk factors.

And I think going to where we want to be, I think there is increasing data now that diets that are higher in sort of whole grains and fibers may be protective against colon cancer and that may be mediated by potentially its effect on the gut microbiome. So one of the questions that we hope to answer in our Grand Challenge Award to investigate not only causes of early onset cancer but also agents to reversal early onset cancer is, are there specific diets that we can start to understand could be tailored in a way to promote a gut microbiome that is associated with lower cancer risk?

So by combining kind of the information we're developing and learning about what sort of gut microbiome is associated with colon cancer, it stands to reason that we can start to maybe develop a diet that may actually modify the microbiome in a way that's healthier and that's associated with low risk of cancer. And that may in part be related to fiber but also may be related to

other dietary components as well. And Ante, we had a lot of questions sort of about two particular aspects of food. So I just want to make sure I ask them really clearly. One question was should we be concerned about nitrites found commonly in deli meals? I think you just mentioned something about processed meats. I'd love to understand that. And another one was back to the question I asked at the beginning about the temperature at which you cook meats and is it important, you know, whether you're eating sort of raw red meat or cooked.

Do you have any views on either of these? Yeah. So the association between red meat and also processed meat and colon cancer, I think, is quite compelling based on the epidemiological studies. The mechanism by which those factors can lead to cancer are less clear. From experimental data, there is a suspicion that maybe nitrates could be a factor. But there's also strong data that supports that. It's not necessarily the meats themselves, but how they're prepared.

So nitrates being a preservative is one factor. And this is all stuff like sort of sausages and salamis and bacons and these sorts of things, Andy. Is that what we're talking about when we talk about processed meats? Correct. Luncheon meats, you know, bacon for sure, are particularly linked to cancer risk. The other dimension is how we cook the meat, as you mentioned. So I think one of the strong hypotheses linking meat to cancer risk has been through the production of certain carcinogens that are generated when you cook meat at high temperatures, in particular the generation of what we call heterocyclic amines.

And that occurs when you char meat. So when you grill it or when you cook at a really high temperature, you tend to form these heterocyclic amines. And those amines, when ingested, causes cancer in animals. So that is a potential mechanism also. So there's, I think, a lot of work to be done to further characterize other potential mechanisms. There's also, I think, quite compelling data that meat alters the gut microbiome in a way that is detrimental and may lead to some, you know, what we call dysbiosis or microbes that are less healthy for you.

In particular, some of the amino acids in meat and the proteins in meat can help to facilitate the growth of certain bacteria that generate sulfur and sulfur reducing, sulfur reduction in the colon, and sulfur reduction in the colon can be carcinogenic as well to normal colon cells. Thank you for listening to today's recap episode. I want to take 30 seconds to talk about something that's not talked about enough. Menopause. Over half the people on the planet experience perimenopause and menopause. Yet symptoms are often misunderstood or dismissed.

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