Harvard Doctor: Obesity, cancer, and the real cost of convenience food | Dr. Andy Chan

0:00Welcome to ZOE Science & Nutrition, where world leading scientists explain how their research can improve your health.

0:14Today, Harvard Medical School professor Dr. Andy Chan reveals new research showing that around half the calories that we eat at home are ultra-processed. Even the meals that we trust is homemade and healthy, stir-fries, salads, even grandma's famous soup could be hiding lab-engineered ingredients you'd never expect. Now, we serve this food to our families every day, but at what cost? Andy's research exposes how ultra-processed foods don't just lead to obesity. They rewire appetite and may even accelerate early-onset cancer. He challenges the myth that younger people can eat anything and still grow up healthy.

0:55But there is hope. Andy reveals the worst ultra-processed offenders, the easiest food swaps, and how small changes by parents, schools, even policymakers could rewrite the future of our health. Dr. Andy Chan is a professor at Harvard Medical School, a doctor at Massachusetts General Hospital, and leads a team tackling early-onset cancers. As a member of Zoe's Scientific Advisory Board, he's here to arm you with the latest research so you can make smarter food choices.

1:30Andy, thank you for joining me today. Happy to be here. Now, I think you know we'd like to kick off this show with a rapid fire Q &A with questions from our listeners. And just to remind you of the rules, say yes or no, or a one sentence answer if you have to. Okay. Are ultra processed foods making us sicker at a younger age? Yes, probably. Could there be ultra-processed foods in a home cooked meal? It depends on how you define home cooked. Is there a simple way to know if a food is ultra-processed? I think there are methods we can use to help people identify ultra-processed food. Are ultra-processed foods engineered to make us want to eat more?

2:14Many are, yes. Could a child's diet impact their likelihood of developing cancer later on? Yes. Finally, you can have a whole sentence. What's the most common misconception about ultra-processed foods? That it's a binary thing, that there's either ultra-processed or healthy. I think there's a gradation. Most of us have this idea that ultra-processed foods mostly come from like a fast food chain or like snacks that we buy from the corner store. But I was shocked when my producer told me, you know, as we were preparing for today's show, that apparently there's some new studies that say around 50 % of the food that we cook at home is now ultra processed.

2:56And so that says it's not just, you know, when we're out and about, we actually need to be worried about what we're buying in the supermarket and taking home. Can you help us understand like, what is ultra processed food and how is it possible that there can be so much of it at home? Yeah, I mean, I think that this is, evolving. I think ultra-processed food has been a moniker that's been thrown around to classify foods in a somewhat simplistic way. I think you're right. I think in most people's conception, ultra-processed food conjures up images of the bag of unhealthy chips or Doritos or the fast food meal that you have on the go.

3:33I think those are kind of the classic conceptions of what ultra-processed food is. But I think that we are understanding more and more that ultra-processing and that terminology can be a bit misleading because I think there are different ways to think about ultra-processed food and there are different ways to think about food processing more generally and also different ways to think about how those different components of food actually influence our health. It is a field that I think has been changing over time. So you're saying it's not just Doritos. What is it? All food, to some extent, that is purchased, you know, that is somewhat ready-made or has been prepared to easily consumed has a level of processing.

4:21And so there are sort of industrial processes by which, you know, the food industry has put food and made it more accessible for people to eat in sort of modern society. I think that the sort of classic conception of ultra-processed food is that it is food that has gone through some level of processing beyond its sort of original form to become more convenient to eat and also oftentimes made to be more palatable, meaning the ingredients have been put together to make them more tasty and more attractive for people to eat. And so it oftentimes does come with a level of processing that makes them more highly preserved, which means they're usually more nutrient dense.

5:02So there's more kind of calories in the food. And also they're made to be tastier so that people can eat them and enjoy them in a more sort of quick fashion. And Andy, I was growing up in the 80s and people are definitely talking about junk food in the 80s. So is this just like a new term for something that is the same that we've always had? You know, was I eating as much ultra-processed food in 1980 as, you know, my kids are likely to be eating today in 2025? It's gradually increased to some extent. I think that when we use the terminology ultra-processed food to incorporate kind of this conception of a level of industrial processing and hyper-palatability, I think that has gone up over the last several decades, even from the 1980s.

5:52So clearly junk food and things that we were eating even back then were ultra processed for sure. But I think because there's been more of an emphasis on providing food that is easier to consume, that is more convenient, that enters into food that we wouldn't classically consider to be junk food. So I think there is a level of ultra processed food that's kind of more hidden than it had been in the past. and that has gradually risen. So now we estimate that, for example, in the U.S. population, over 50 % of the food, maybe even up to 75 % of the food that we actually consume would be classically considered ultra-processed food.

6:27So that's clearly a lot more than just the bag of Doritos and the candy that I'm sort of thinking about. Why is it so prevalent in our diets today? What has been changing over the last 40 years? Well, I think there has been a greater emphasis on convenience. I think because we have obviously seen our, you know, societies become more complicated in terms of the things that people are doing. I think in general, people are busier and multitasking during the day in terms of work, doing things at home. I think all those kinds of things have compounded to kind of put a greater priority on having foods and meals that are easier to prepare and reduces the burden on us in terms of time for food preparation, food shopping, and putting meals on the table.

7:14So I think that sort of level of convenience and the need for that has sort of been driving some of this increase. And then I think there has been, I think, this idea that over time, as people have become more accustomed to kind of the taste, if you will, of ultra processed food, our palates have maybe adjusted such that people are now seeking out those kinds of foods more and more as kind of, you know, foods that they enjoy and sort of trigger some of the reward mechanisms in our brain to make us sort of seek out these foods. So I think there's probably a combination of societal shifts in terms of what we prioritize in our meals and also just changing taste in terms of what we enjoy eating.

7:57And that, I think, has adjusted over time. And we've seen that clearly in, you know, the sort of classic Western countries or countries that are sort of high income. But I think that's gradually becoming more prevalent in, you know, other parts of the world. And that's reflected, I think, in sort of a global trend toward increasing consumption of ultra processed food. And also with that has come maybe some global trends that we've seen in disease incidents. I like to do a little drum roll when announcing something exciting at Zoe. And that really exciting thing is that our plant-based gut supplement, Daily 30, is now available in the U.S.

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10:07That's Zoe.com with the code FEEDYOURGUT at checkout. You could be one of the first in the US to try the gut supplement that's changed my day, and I know it'll change yours too. And Andy, when I hear you talk about sort of convenience and changing tastes, it feels like this is all driven by like active choices by us as consumers when we go to the supermarket. But I've definitely heard other guests talk about the role of the food corporations themselves in terms of maybe like engineering these foods to make us want to eat them more or just figuring out that they can save money or make the food in a particular way where they're not really worrying very much about any of the health impacts that might come from UPF.

10:56Is that all scaremongering or is this true? I think the truth is in between. I think it's a combination of people's choices and the choices they're making about food in combination with what they have access to and also in combination with sort of what is being provided to them commercially. And obviously those things work hand in hand. And so as people's tastes change over time and the kinds of foods they seek out change over time, it obviously changes the calculus for people who manufacture foods and for people in the food industry to provide foods that meet customer wants and needs. And then to some extent, that also feeds into itself where I think some of these companies and some of the people who are responsible for our diets are gradually making changes to also try to encourage people's food taste to go in a certain direction.

11:46I actually had a conversation with a food scientist who worked for a company that I won't name who described just year after year, you know, testing different variants. And the test is really straightforward. It's like whichever variant, you know, when you go and do a taste test, people just eat more of, that's the one you ship. So like each year, they're very cleverly using all this food science to try and figure out how you can eat a few more cookies or a bit more of this thing. Now, he was just one person, but is that a part of what's driving this? Yeah, I mean, I think there's very clear evidence that that's happening.

12:20I think we're also seeing kind of in the opposite direction. I think we're seeing obviously some evidence that an increasing proportion of the population being on some of these new anti-obesity drugs like GLP agonists, those drugs are probably also changing consumer preferences in terms of the food they're eating. And so I think there's evidence that the food industry is looking at that carefully and trying to decide whether they need to also adjust some of the offerings they make available to the population so they're meeting those changing preferences. And if you start going on those drugs which make you less hungry, does that mean that you're actually sort of craving these ultra-processed foods less?

12:59Is that what you're saying? I think it looks like that may be the case. I think it seems like, you know, the early evidence is that these drugs are, you know, also affecting our preferences in terms of the kinds of foods we're choosing to eat. And that may have to do with kind of the shift in sort of our brain-gut axis and trying to sort of shift our preferences as to the kinds of foods that make us feel full and the kinds of foods that we enjoy. There's something slightly crazy here, isn't there? So we eat all of this food that, you know, we were never evolved to really eat steadily over years.

13:31It makes us sick. We end up in this horrible sort of hunger cycle that can end up with us living with obesity. Then we take these marvelous new drugs to sort of switch that off so that we no longer want to eat the food that if they weren't selling on the supermarket stores would probably never get us there in the first place. That's sort of how I understand it. There's a bit of a swing. You know, I think it's an interesting way to look at it. But I think, you know, it's the population shifts that I think are what drive maybe what we're seeing being offered more and more by the food industry. It's really interesting.

14:03I know your studies a lot look at those sort of overall population shifts. So I'd actually love to go down to this individual study that you published very recently on ultra processed food that you ran at Harvard. Because I think it helps us to understand one of our most common listener questions, which is like, are these ultra processed foods making us sicker at a younger age? And I understand that you chose a very particular group of people to study, namely kids. Why did you choose to study kids? Because I think children are really active, so surely they can get away with eating a lot of this sort of junky food without bad effects.

14:42Well, I think that this really came out of our desire to understand a little bit more about why we're seeing this trend in obesity rates. We've clearly seen in the U.S. and other countries that obesity has risen dramatically in the population. And it's not just adults, it's also younger people. So we're also seeing rates of childhood obesity really rise dramatically as well. But, you know, the reasons for why we're seeing that increase in obesity haven't been so clear. I think there's been an assumption that we're just eating more. But to the point, I think in the last several decades, we've actually seen that probably caloric intake in general may actually be, you know, not shifting dramatically, that it's not just we're eating more calories, but that there might be some differences in the types of calories we're eating.

15:31So we really wanted to kind of understand why are we seeing these dramatic shifts in obesity rates, particularly in younger people. In addition, we're also seeing that there are dramatic differences now in rates of chronic disease in younger adults that we haven't been seeing before. So we're seeing more and more rates of cancer in younger people. I think that that's an area that I've particularly focused on is trying to understand what are the reasons for why younger people are getting cancer. So because of that, I think that there is maybe this shift in risk factors that are happening at younger ages.

16:04That may be some of these things that we're thinking about as being risk factors for disease later in life are actually shifting into younger ages. So I think we need to really focus and have more attention on what younger people and children are being exposed to and not just adults. And Andy, is it only cancer that is increasing in younger people? That's been the most dramatic change. You know, we're seeing dramatically increased rates of different types of cancer in younger people. I think that's been a very noticeable trend. But I think we're also seeing, you know, changes in other types of conditions as well.

16:36As a gastroenterologist, for example, we're seeing rises in, you know, inflammatory diseases of the bowel. We're seeing rises in inflammatory bowel disease, for example. we're seeing obviously changes in overweight obesity over time. We're seeing also consequences of that rising over time, like diabetes, et cetera. So I think we're seeing a lot of these sort of metabolic diseases and inflammatory diseases happen at earlier ages. And that probably reflects what we're seeing in cancer as well. And when you say younger people, the older I get, the more I want that to include me. What do younger people mean is you're talking about that as a doctor and a scientist?

17:11Yeah. I mean, I think for cancer in particular, we generally define early onset cancer in younger adults as being less than 50. Because in the past, I think we've kind of considered cancer to be a disease primarily affecting people over the age of 50. And that's really why most of the common cancers that we screen for, we start that screening at the age of 50. And so I think in the sort of common definition of early onset cancer for our studies, we've really been focused on people younger than 50. Could you maybe summarize the study, what you did and the findings? Yeah, so we really were wanting to focus on, as you said, younger people to kind of understand what are younger people being exposed to in terms of risk factors and how does that affect not only their health as young people, but in later life.

17:54So we wanted to develop this study within a cohort of younger people that we've been following longitudinally since they were very young over time. So it's called the Growing Up Today study. And these are a group of children that have been followed because they were offspring of mothers who were already in a study. which is called the Nurses' Health Study II. And these were a group of female nurses in the U.S. that have been tracked with questionnaire data since the early 1990s. So this is like a 35-year study at this point. Right. So we have a unique opportunity to look at this group because we have data on the mothers and we also have data on their children tracked over the last 30 years.

18:34And so having sort of that combination of data is really unique and being able to then really pinpoint risk factors, not only in the kids when they're growing up, but also look at risk factors in the moms at the same time. And also even some of the things they're exposed to when they were pregnant with those kids. So we have kind of data on both the moms and the kids. So we really wanted to look at what the diets of these kids were like and what the diets of the moms were like and assess whether diet and the things they were consuming affected their risk of developing overweight obesity later in young adulthood.

19:10So we carefully looked at information tracked on what they were eating and then assessed whether, you know, a substantial component of their diet was related to consumption of what we would consider ultra processed food and then assessed whether that consumption of ultra processed food associated with their likelihood or risk of developing overweight obesity in the future. So what did you find out? It was very interesting. I think we did find there was an association between child consumption of ultra-processed food and future risk of obesity. Perhaps that wasn't so surprising. But what was very interesting in particular was that it also was associated with the likelihood of their moms eating ultra-processed food during that period of time where they were raising their kids.

19:54And it was sort of an independent risk factor. So what the kids were kind of exposed to in the household seemed to actually have a direct influence on whether they were subsequently at higher risk of developing obesity. We did some additional work looking at the association of, you know, moms' diets when they were pregnant with their kids. There seem to be some association there, not quite as strong, but it does look like early life factors and particularly maternal risk factors seem to be important in determining a child's health over time. I heard you mention that it's not just that you're eating more calories if you're eating this UPF, if I understood rightly, that sort of the quality of the food is something that you were saying actually really makes a difference.

20:41And could you help us to understand that? Yeah, I mean, I think what it implies is that a kid's diet has to do with what they're eating, but also has to do with what other foods are being consumed in the house and kind of what they're exposed to. So sort of, you know, everyone's diet is also in part, not just their individual food choices, but also what food they have access to. So the idea that a household's access or a household's propensity to be eating ultra-processed food influences their later health, I think, is an important message. In addition, I think that that sort of shows kind of a practical association.

21:16But also there's biological questions as well. Is there exposures that might be related to differences in exposure to ultra-processed food, for example, in utero? So a mom's diet, does that influence their kid's health? Yes, certainly in the short term. I think we know that a mom's diet obviously affects the newborn period, but does it also have potential effects downstream from that? And it does raise interesting questions about that because it is possible that some of the sort of short-term, you know, dietary exposures that someone is exposed to when they're, you know, in utero, what we call biologically imprinted such that it has an influence on their later health status.

21:57And that's, I think, a really interesting possibility and one that's being explored more and more. I think you're saying that the food that a mother is eating while she's pregnant could actually affect sort of the health of their child like 20 years later. And that if they're eating lots of these ultra processed foods, that could actually be harming their health 20 years later? It's very possible. I mean, I think that that's really the hypothesis that we're pursuing. Trying to disentangle how much of that is sort of what the kid's exposed to and what they're doing from what their mom's doing is part of it.

22:33But also, you know, understanding is there an independent effect of what the mom's doing that still has a lingering effect on the child when they get older? And I think that that's the thing that we're really trying to tease out. I mean, so the first thing that I always think whenever this comes up is it's really, really tough being a mother. Like there's so much guilt about trying to do a good job, you know, when you're pregnant and then, you know, when the baby's born and you're supposed to breastfeed. And every time we have this sort of conversation that is almost just like layering on more guilt.

23:03On the other hand, I think it's important to understand what the science is saying. I think we're used to the idea that you shouldn't smoke when you're pregnant. I don't quite understand how it works, but it seems sort of clear that smoking is really bad. And it's not bad just, you know, for the nine months that's going on. It's sort of obvious that it's like not setting your baby up well. I think lots of people will be really shocked to say that UPF foods would be bad. Because I think we mainly associate with, you're just going to eat sort of too much of this, right? It's sort of too yummy. And so you're going to like overeat.

23:34And so you're going to, you know, you might put on weight as a result. but saying that it's actually like long-term harmful sort of makes it sound like more in the category of smoking or alcohol rather than you know don't eat too many calories yeah i think it's it's a very complicated issue and i'm glad you raised that i think one of the things that we are trying to really avoid is this idea that you know there's a stigma around diet and and people's food choices. I think that's not our intention whatsoever. And we recognize that mothers and certainly people in general are doing the best they can in terms of making food choices.

24:14And sometimes, you know, those food choices are dictated by other factors that they don't have control over. The kinds of foods that are available to them, you know, in terms of food access, in terms of both economic issues around sort of food access and also, you know, economic issues and sort of where they're living and sort of their ability to access fresh foods. Those are all factors that I think are beyond the control of an individual. But I think it does also suggest the need for us to look at this more closely, because I think if we start to see evidence that maybe some of these factors are important to consider when someone is pregnant or when they're raising their kids, it does have implications for sort of recommendations we make both to individual people, but also what we recommend, you know, as a society and what we're willing to offer people as a society and what we should prioritize as a society in terms of access to food, etc.

25:11There is sufficient evidence to really consider that there is, you know, implications for people at every stage. So the learnings from this are just as relevant at the point that you're an adult. At every stage of life, whether you're male or female. I mean, I think these are the kinds of things that we're kind of understanding. So at this point, you said you got this study and you're eating all of this ultra processed food is not good. Do we have any understanding why that is the case? Because I guess that would then help us to understand better what needs to be changed. Yeah. So I think that's the key question.

25:44That's the key next step. So I think we alluded to this at the beginning is that we're understanding that ultra processed food, I think is a useful framework, but I don't think it's sufficient for us to really get at what's cause and effect and also really get at what are the underlying reasons or mechanisms by which some of these foods may be causing health problems like obesity or cancer. It's a useful starting point and a useful framework for us to think about it. But I think we have to do more to understand why it's potentially triggering disease risk and also what components of ultra processed food are of, you know, specific concern for two reasons.