ZOE Science & Nutrition - Recap: How ultra-processed food impacts your brain | Prof. Felice Jacka

Episode Date: May 20, 2025

Today we’re exploring the impact that ultra-processed foods have on our brain. We often think of nutrition in terms of physical health - things like obesity, heart disease, or diabetes. However, what we eat also plays a crucial role in our mental health, influencing mood, cognition, and even our risk for conditions like depression. So, what can we learn from the studies that have looked into the connection between food and thought? I’m joined by world-leading Professor of Nutritional Psychiatry Felice Jacka to explore this fascinating link and discuss how we can make smarter food choices to keep our minds sharp and healthy. 🥑 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 Zoey Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're exploring the impact that ultra-processed foods have on our brain. We often think of nutrition in terms of physical health, things like obesity, heart disease or diabetes. However, what we eat also plays a crucial role in our mental health, influencing mood, cognition, even our risk for conditions like depression. So what can we learn from the studies that have looked into the connection between food

and thought? I'm joined by world-leading professor of nutritional psychiatry, Felice Jacar, to explore this fascinating link and discuss how we can make smarter food choices to keep our minds sharp and healthy. Neuroscientists discovered probably the end of the 1990s is that we have this region of the brain called the hippocampus. Now it's only tiny, they're two little bits that sit together in the middle of the brain. And Felice is holding over, for those of you just on audio, she's holding her hands like very small. So you're saying it is like- Yeah, probably a lot smaller than that.

Like really small. But this hippocampal area of the brain seems to be very important in learning and memory. Okay. It also seems to be really important in mental health. So there are particular proteins that grow new neurons in the hippocampus. So the hippocampus can actually grow and shrink over the life course.

And is that unusual? Is that? It's the only bit of the brain that we know of that does this, where you can actually grow new neurons and it can get larger. So the rest of my brain, I am right, basically, it's not growing anymore. All that's happening is sort of I'm losing capacity. It does look like that. And people, as they get older, the hippocampus shrinks and that's when you start losing your car keys and forgetting your kids.

So this is linked to dementia. Very strongly linked to dementia. But of course it's linked to learning and memory right across the life course. So it's relevant for children as well, their ability to learn and remember. It's relevant to, you know, people in middle age in their jobs and their, you know, ability to function in the world. Now, what we see over and over again is that the quality of people's diets is linked to the size of their hippocampus. Now, we've seen for many years.

I just want to stop you for a minute because you just said something really radical and I just want to make sure that, because you just said the hippocampus is sort of central in our learning and memory. It's the only part of our brain that keeps growing, that can grow as we get older. And then I think you just said very casually, but I just want to pick up, oh, and by the way, the size of it is like directly related to the diet that we have. That's exactly right. So when the hippocampus was identified as this region of the brain that grows and shrinks,

part of that was because they could see that people with major depression, for example, had a smaller hippocampus. And when they were successfully treated, their hippocampus got larger. But there was actually a whole lot of really cool research in animals in the early 2000s. And it's one of the reasons I got really interested in this idea of nutritional psychiatry, where they could manipulate the size of the hippocampus and also the animal's sort of learning and memory by manipulating exercise, which affects the hippocampus, and diet and showed really quite profound effects. So in 2000, I think it was about 2013, I did the first study in humans to look at this.

So we'd been working with this large epidemiological study. So that's when you're just observing people, you're not intervening, you're not doing an experiment and it was a large cohort of people in Australia and we'd already seen that the quality of their diets was linked to the risk of them developing depression for the first time as they got older, independent of a really wide range of really important socioeconomic factors, income, education, these sorts of things. And then recognizing that there were brain scans done on a small cohort of the older people, about 250, I thought, oh, this is a great opportunity. So we actually looked at the hippocampal size of people as a function of their diet quality.

And of course we took into account depression, we took into account all of those other factors. And what we saw was a very clear link between the size of people's hippocampi and their diet quality. And it wasn't just a tincy little effect size. It was equivalent to about 60% of the shrinkage that you see in the hippocampus as people get older. That's amazing. So you're saying 60% of the amount that somebody's, this part of this critical part of your brain shrinks is down to whether or not you were having like a good diet or a bad diet. Well, this is observational.

So we can't say definitely it's causal, but it was a very clear dose response. Since then, there's been two other studies, one done in the UK with the Whitehall 2 cohort that showed the same thing, diet quality, very clearly linked to people's hippocampal volume, particularly alcohol. So if you drink, it looks like you'll have a small hippocampus, even a small amount, which is a bit depressing. That'll depress Tim, who's always looking for a reason to say you can have one glass of red wine a day.

And then in the Netherlands, they did an even larger study, more than 4,000 people, and showed that the quality of people's diets was linked to not only the hippocampus, but other regions of the brain and total size, gray and white matter volume, taking into account all these other factors. So it looks like diet is really clearly linked to your hippocampus. Now this is incredibly important when you're thinking about your brain power. Now it's not just learning and memory. The hippocampus seems to be a key part of our emotional regulation systems.

What we see in animal studies is if the animals are manipulated so that they can't produce the protein that makes the new neurons in the hippocampus, antidepressants don't work. that makes the new neurons in the hippocampus, antidepressants don't work. So there's some thinking that actually the hippocampus is a key way in which antidepressants can improve mental health. But the other thing the hippocampus does is it helps to regulate your appetite. It sounds like it does everything. Well, it's a really, you know, your brain is amazing, right? And it does all sorts of things. And a lot of what we know is coming from animal studies, because, you know, it's very difficult to chop humans' heads off

and have a good look at their brains. Which is good to hear. Yes. We do have two very cool studies, though, that have actually manipulated diet, just for the short term, in young, healthy people. So tell us about them. So these two studies were done in young, healthy, lean people, right?

So they're not overweight, they're obese. In the first study, they gave them just over four days, a breakfast of toasty's and a chocolate milkshake. And toasty's is? Oh, just like, you know, a toasted sandwich, probably with cheese or something in it. But in one group, their version of that was very high fat, high sugar, and the other version of that wasn't, and they were randomly assigned to both.

And what they saw was that within four days, they could see an impact on this hippocampal-related learning and memory tasks in these young people. Wow. So they changed the breakfast and in four days. In four days. And then the second study, and this is in over a hundred young healthy people, they gave one group, you know, the same breakfast, and then they sent them off with some vouchers for well-known food chains, told them to have Belgian waffles or something similar for breakfast and to have the rest of their meals from these

food chains. The other group were given the healthier version of the same breakfast and then told to continue their diets. Now, it should be said these people all had reasonable diets to start with. They weren't eating a whole lot of junk food. Similarly, after a week, they saw the same impact on hippocampal dependent learning and memory tasks. And it seemed to be particularly pronounced in those who had a very strong glucose response to the diets. So like not good control of their blood sugar, is that what that means?

That's right. Yeah. So what also happened in those, in both of these studies is that people consuming these unhealthful foods also had lower appetite regulation. So we know that people, when they're eating ultra processed foods, they seem to eat more, even when they say, oh, the food is just as tasty or, you know, and we know this from randomized controlled trials in the states, very famous trial done by Kevin Hall. But we don't really know why. Well, in these studies, it looked like it affects the hippocampus and it seems to do so through glucose regulation. And that seemed to affect appetite. So people were more likely to want some more of these types of food. So it's saying that what you eat has a really important influence on your hippocampal volume

and your hippocampal function, which could affect your learning, your memory, your mental health, your appetite regulation. In the second study, they tested people again three weeks later when they'd reverted back to their normal healthy diet. All of those deficits were gone. So it suggested once they stopped eating those foods, they actually, their brain kind of went back. Maybe the hippocampus is very plastic, so it probably grew some more neurons. And so what would this mean over time, Felice? So imagine that, you know, I eat a diet of ultra processed food for the next decade and

you don't. Like, what does this mean in the long run? Because you talked about like these sort of short term effects on sort of maybe something you can measure in your hippocampus, but what would it actually mean to somebody in terms of their health and capabilities? Well, we know from, again, the epidemiological literature, so this is when you don't intervene, but you're just looking at people, large groups of people that you are assuming are representative of the population, and we see right across the world this clear link between the quality of their diet and their risk for these common mental disorders. So that's depression and

anxiety. These are very common. They're very, very burdensome. So at the population level, it looks like right across the life course, if people are eating a less healthy diet, and it has an influence on mental health. What practical, I'd love to switch maybe now to practical advice. Maybe let's start with children and let's think about maybe for our listeners and also maybe also thinking about people as we get really quite old. Any practical tips for us about what we should do? How do we identify this UPF? What should we be worried about? And what could we do about it?

Think of these sorts of foods like ultra ultra-processed foods, and these foods that have got a lot of added sugar and salts and fats, they're all designed to interact with the reward system of the brain. Well, they're probably not explicitly designed for that, but they do, they interact with the reward systems of the brain. And for children and adolescents,

those reward systems are particularly sensitive, if you like, and there is some evidence, I believe, that suggests that it is programming the immune system and inflammation and the reward systems of the brain when they're young, if they're exposed to it, so that they will want to keep eating those sorts of foods. They'll make those choices. And is this all or nothing? Or can anyone listen to this say, you know, either from myself or from my family, maybe I can't cut out all of these ultra processed foods. You know, is there a certain amount, is it better if you reduce it?

Definitely. And so what we've seen in our latest study, so this big sample of Australians, is that it's only those in the very top quartile, like that top 25 percent of consumers of ultra-processed foods that had the increased risk for depression. Now, you want to normalize healthful foods, but we recognize that so many people have challenges with access, maybe storage,

maybe food preparation, education. It's going to take time to overhaul our whole global food system. There's huge pushes on to do this. There's big players and things happening at the level of both the industry, but also government that I'm hopeful will start to feed into changes in the way we produce foods, changes in the way we market them, all the rest of it. But governments have to get real about food policy because we're talking about the whole health of the population.

But in the meantime, if people are consuming these foods, even just small reductions are going to help. I hope you found the information in this week's episode useful. If you're interested in improving your gut health, you might want to download our free Gut Guide. It's packed with recipes and science-backed information to help you on your journey towards better health. Go to zoe.com slash gut guide to download it for free. Or if you're looking for another podcast to listen to, we have a lot more in our back catalogue. Would you like to know how to reduce your risk of dementia?

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