Can a traditional African diet help protect against inflammation? With Quirijn de Mast and Tim Spector

In this groundbreaking episode, Jonathan, Tim, and guest researcher Prof. Quirijn de Mast explore a landmark clinical trial conducted in partnership with Tanzanian scientists and community members at the Kilimanjaro Christian Medical Centre (KCMC).

Published in Nature Medicine, the study investigates what happens when people switch between Western-style eating and a traditional diet from the Kilimanjaro region of Northern Tanzania — rich in fermented foods, legumes, ancient grains, and green vegetables.

The results? Rapid, measurable changes to immune function, inflammation, and gut health — with powerful implications for global disease risk.

This episode explores scientific research on traditional East African diets and inflammation, led by Quirijn in close collaboration with Tanzanian scientists and participants.

As Western scientists and hosts, we are aware of the need for humility when discussing cultural traditions not our own, and we approach this conversation with deep respect and curiosity

Transcript

Jonathan Wolf: Quirijn, thank you for joining me today. 

Prof. Quirijn de Mast: Thank you. Lovely to be here. 

Jonathan Wolf: And Tim, thank you for joining me as well. 

Prof. Tim Spector: Likewise. 

Jonathan Wolf: Quirijn, we always start the show here with a rapid-fire q and a, with questions that come from our listeners, but we have some very strict rules, very hard for scientists. You're allowed to say yes or no, or a one-sentence answer, if you absolutely have to. Are you willing to give it a go? 

Prof. Quirijn de Mast: I'm ready. 

Jonathan Wolf: Can a traditional African diet really transform your health? 

Prof. Quirijn de Mast: Yes. 

Jonathan Wolf: Do you need to wait months before getting the benefits of an African diet? 

Prof. Quirijn de Mast: No, certainly not. 

Jonathan Wolf: Tim, is the Western diet harming people?

Prof. Tim Spector: Sadly, yes.

Jonathan Wolf: Is a traditional African diet healthier than the Mediterranean diet? 

Prof. Tim Spector: Not necessarily. 

Jonathan Wolf: Alright. Quirijn, for a Western listener, what's the most exciting thing about an African diet? 

Prof. Quirijn de Mast: I think what excited us the most as researchers was the clear effects, the immune effects of a traditional fermented beverage that we used in the study.

Jonathan Wolf: Everyone has their Achilles heel when it comes to tempting treats. And Quirijn was telling me that he was raiding the breakfast buffet of the hotel he was in last night. 

It's funny because for me it's fresh bread, it's chocolate, and actually it's that ultimate combination where they put the fresh bread and the chocolate together and they make a pain au chocolat or chocolate croissant depending on where you are.

And all of those are sort of key foods in the Western diet, and that diet in general features a lot of processed meat, high sugar drinks, and refined grains. 

I'm very excited to be talking about a completely different diet today, and to be speaking with a scientist behind the very first significant clinical trial of the Sub-Saharan African Diet, published in the world-leading journal Nature just a few weeks ago.

But just before we dive into it, actually, I thought maybe Tim, you could just summarize what's the problem with the Western diet? 

Prof. Tim Spector: The Western diet, also known as the SAD diet or the Standard American Diet, is basically responsible for millions of deaths a year through the chronic diseases that it's causing.

So, obesity, diabetes, heart disease, cancers, autoimmune disease, mental health problems, you name it, this has been linked to our poor diets. So, anything we can learn from other populations about how to manipulate or change our diets, looking at other examples, is really important for our health.

It's becoming increasingly true that it's not just about the fats. It's not just about the calories. It's about something else in the food that is upsetting our immune systems, our bodies, and our gut microbes in ways that in the past we haven't really thought about. 

So thinking about new mechanisms about how other diets might be beneficial is really absolutely vital for us moving forward to really redesign the way we eat and think about food.

Jonathan Wolf: I already asked about this Mediterranean diet versus African diet because I think we hear about the Mediterranean diet often as the answer. Tim, why is that? 

Prof. Tim Spector: That's probably because most data worldwide comes from our study of the Mediterranean diets. Since the 1950s, we've been really looking at that as the model of why there was this big difference between North and South Europe in terms of heart disease. That's how it all started. 

American researchers like Ancel Keys did these big epidemiology studies following populations that were eating lots of dairy and fatty foods, but with large amounts of legumes and vegetables, fresh fish, et cetera, and plenty of olive oil. He found they had a third of the rate of heart disease of the average American.

So it was this idea that we should be somehow mimicking what they were eating in Southern Europe, in Greece, Italy, and southern Spain. And if we could recreate that in Northern Europe and North America, then we would actually dramatically help improve our health. 

So that idea has been with us for over 50 years now, although it's been very difficult to define the Mediterranean diet. And if you go to the Mediterranean now, you'll see pizzas, and pasta, and that isn't what they originally thought of as the Mediterranean diet. 

So this is the problem, and that's been exported. There are pizza places everywhere in the world now. It doesn't mean that's now the healthy diet. Places like Italy are getting increasingly obese and having problems as well.

So it's trying to define what are the key elements in these diets that are helpful, rather than just saying, Oh, well, just eat like the Italians or the Spanish and you'll be fine. 

Jonathan Wolf: So, Quirijn, it's really exciting to have you here because I think we've tended to speak a lot about the Mediterranean diet across many different scientists on this podcast.

This is the first time, actually, that we're talking about a traditional African diet. Could you start by just telling us what is a traditional African diet?  

Prof. Quirijn de Mast: It's not easy to define because there is not a typical, traditional African diet. I mean, Africa is a huge continent, and there's so much diversity in dietary patterns across the different regions.

That said, there are some unifying themes. If you talk about African diet, so many of the traditional African diets, they're mainly plant-based. That's one. 

So people consume a lot of legumes, traditional grains like millet, sorghum, and teff in Ethiopia. And these are very, I would say, interesting small grain cereals with many health benefits. 

But also, they have a rich tradition in Africa in using fermented foods. 

Prof. Tim Spector: They also have a lot of porridge, don't they? The thing we don't do is that they put all different grains into a sort of gruel and porridge. 

That seems to be what I've noticed in Africa. The grain might be different, but they still have a similar base of many meals. Like we would have potatoes. They have a sort of grain porridge. 

Prof. Quirijn de Mast: Yeah, that's correct. So in Tanzania, where we did our studies, people consume two, sometimes three times daily, indeed, a porridge.

It's made of mace or millet. But you see, in many areas that they have their local porridge. It can be made from, mace, can be made from, from sorghum, for example. So that's true. Yep. 

Jonathan Wolf: And you've mentioned quite a few grains that I'm not familiar with. Sorghum, I wouldn't know if it dropped on my head. 

Could you describe for listeners who maybe are not familiar with a millet or a sorghum? What are they similar to, that we might be used to finding in a Western supermarket?

Prof. Quirijn de Mast: To be honest, I can't really compare it to what we are used to in Europe or in Western supermarkets. 

But they are extremely interesting, these grained cereals, because they're so nutritious. They contain lots of fiber, more than, for example, wheat. They are rich in polyphenols. They also have a low glycemic index, so you don't see this spike in glucose or insulin when you eat them. 

Yeah, they're kind of neglected, I would say, but they have very interesting health benefits. 

Prof. Tim Spector: So there are many grains that our ancestors used to eat, and we've all become very focused on these monocultures of just having maize and wheat as our principal ones, and they're the ones we export.

But if you go to other countries, you'll see all these varieties of these cereals, and it turns out they're much healthier than the ones that we've evolved in that we're just more efficient for storing long-term and big commerce, sort of global commerce. 

So this is why when you go to Africa, you'll see a lot of these regional grains that we don't see anymore in the rest of the world.

Jonathan Wolf: So I should think about these as being like the seeds of these plants, a bit like I might have with wheat. And these are traditional plants that, as human beings, we've presumably cultivated for very long periods of time in Africa. 

Prof. Quirijn de Mast: Yes, correct. Yeah. 

Jonathan Wolf: But we haven't traditionally eaten them. If you're listening to this in the States or Northern Europe, or probably Australia, or Canada, or wherever, they somehow never really made the transfer with people as we came out of Africa. 

Prof. Quirijn de Mast: No, not that I'm aware of. So we don't have a tradition of eating millet or sorghum. Indeed. 

Jonathan Wolf: And what made you want to study this African diet, Quirijn? 

Prof. Quirijn de Mast: Well, it's one of the reasons, it's my own observation. So I've been collaborating with the University Hospital in Northern Tanzania, KCMC, so it's the foot of Mount Kilimanjaro.

I've been collaborating with them for almost 20 years. So, 20 years ago was my first visit. I was doing a PhD on malaria, and since then I've been a regular visitor.

I do see clear changes in disease patterns over these past 20 years. So 20 years ago, if you would look in the hospital, there were mainly people with infectious diseases.

But nowadays, you see this very rapid rise in people with non-communicable diseases or lifestyle diseases. So there's a lot of obesity, a lot of type 2 diabetes, people with cardiovascular disease, and kidney failure. 

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So we are interested in what does cause these changes in disease patterns. My department, our research, just focuses on factors that reregulate your immune system.

We've been doing different studies in the Netherlands, in cohorts of healthy people and people with underlying conditions. But we thought it would be of particular interest to also perform these studies in Africa, in Tanzania, to look at what are the factors that regulate your immune system.

Because if you talk about cardiovascular disease, for example, we know that there's an essential role for inflammation. And so we conducted, some years ago, a larger study, over 300 healthy people. 

Some of them were living in a city, some of them were living in a rural area. And we looked at all these factors that might associate with the function of your immune system.

And what stood out was what people eat. These studies, we call them cross-sectional studies. So you look at one time point. So we had a clear hint that the change in diet between people living in the city and people living in a rural area was one of the main factors driving inflammation and the function of the immune system.

But we wanted to confirm that it's indeed diet, so that's why we did this intervention study. 

Jonathan Wolf: Can you maybe draw a picture for the many listeners who have never been to Tanzania? What was it like when you first visited 20 years ago, and what is it like now?

Because you're painting a picture, I think of a lot of modernization, and a rise in diseases, that I think will probably be surprising to most listeners, 

Prof. Quirijn de Mast: Yeah, it's totally different. So Tanzania is a country in East Africa. It has a steady economic growth, so it's now a middle-income country. More and more people living in cities.

And in the city, life is like what we know from the Western world, people are surrounded with processed foods. There is fast food on each street corner. There is snacks everywhere. 

Jonathan Wolf: So they're now eating hamburgers, and French fries, and lots of processed food in packets produced by big companies.

Prof. Tim Spector: Yes. Every street corner has brightly colored stalls with soft, fizzy sodas of every single bright color of the rainbow. Really fluorescent colors. The thing you notice most when you go to these countries.

And these snacks that last for years, that never go off. Big food companies have got their first, they've made sure that these foods are everywhere, and they're cheap and available.

Prof. Quirijn de Mast: And another thing that I notice is that, so 20 years ago, people would walk a lot, but nowadays, there are motorcycles everywhere. You know, these motorcycles are imported from China, and tuk-tuks. People have a much more sedentary lifestyle. 

So these are two major changes. What's interesting in the Kilimanjaro region, where we did our study, we have a town, it's called Moshi.

Moshi lies at the foothill of Mount Kilimanjaro, but very nearby on these foothills of Mount Kilimanjaro, people still live a traditional life where they still exercise a lot, they walk a lot, but also they preserve their traditional diet.

So that makes this a very interesting area to look at the effects of lifestyle changes and dietary changes on health. 

Jonathan Wolf: It's almost like a time machine where you can look back into a diet of people living in pre-modern, western lifestyle and then literally next door, you've got people who are now living the sort of diet that you would be living if eating, if you were in New York or London, or Amsterdam.

Prof. Quirijn de Mast: Exactly. Yeah.  

Jonathan Wolf: I had no idea how fast that change was happening. And I think I'm also rather shocked to hear how much these sort of Western diseases, we tend to think about them as Western diseases, right? The diabetes and the obesity. 

And you are saying that now in Tanzania, which only 20 years ago, you're saying that almost nobody was eating these foods, and you really see the impact already today on things like obesity.

Prof. Quirijn de Mast: Oh, absolutely. So in an urban population, so people living in cities, 30 to 50% of the adults are overweight or frank obese.

 It is immense. So it's a huge challenge for healthcare nowadays.  

Prof. Tim Spector: And generally, when I've been to Kenya and Tanzania, they believe that western food is more likely to be healthy for them because it's seen to be associated with being rich and wealthy, and therefore more advanced.

Even if it comes in a bright green packet, it's seen generally as something that you should aspire to. So there's a big gap in education about what is good and bad. 

Jonathan Wolf: Well, I think you've painted a really powerful picture for why you'd be really interested to understand whether the diet change is what's behind this change in health that you're describing.

And I think we've got a bit of a picture also of what this African diet is, and it's clearly very, very different from the Western diet. 

Your team was the first ever, as far as I know, to comprehensively try and examine the effect of a traditional African diet with a very strong study structure where you could really actually do an intervention and see what happened.

Could you describe in simple terms what the study was and then we'll go on and talk about what you found out. 

Prof. Quirijn de Mast: Yeah, so we selected a group of healthy young men. Half of the men were living in the city, and they were consuming a Western-type diet while the other half of the young men were living in a rural area. So up Mount Kilimanjaro, somewhere, almost 2000 meters. 

So what we did was set up a study site up on Mount Kilimanjaro. So kind of a pop-up restaurant on almost 2000 meter altitude. With a cook. 

The rural living man, we would switch the diet to a Western-type diet. So they would come three times daily to our study site, to our pop-up restaurant. They get breakfast, they get lunch, they get dinner. 

And then we measured the function of the immune system. We did that with blood tests, and we sampled a microbiome. We did that at the end of the two-week intervention, and then they would switch back to their habitual diet.

But we resampled them four weeks later, because we were also interested in the longer-term effects of this, such a short intervention. 

In the cities, we did the opposite. So the man, they had a western type diet, and so we switched them to this traditional Kilimanjaro style diet. So we gave them lots of beans, traditional grains, the millet, sorghum porridge, for example, again, with the same, resampling four weeks after the end of the intervention.

We did exactly the opposite. So we switched basically their diet, so Western to traditional and traditional to Western. 

Prof. Tim Spector: Do you remember roughly the difference in fiber consumed per day? 

Prof. Quirijn de Mast: Yeah. So on the heritage diet, people would consume roughly 90 grams of fiber a day, while in the Western diet was roughly 30 grams a day.

Prof. Tim Spector: Wow, that's a big difference. And just so people know, the average American in the west has about 15 grams of fiber per day. 

So 30 is actually a recommended level. So it's, it's not bad, but you get three times that in the African diet. That's amazing.  

Jonathan Wolf: So I'm just doing my little mental math. You're saying that the traditional African diet goes from 15 grams, you see in America, on average, all the way up to 90. 

So it's six times more fiber they're eating every day. So, you know, we talk a lot about a deficiency, but that relative level is extraordinary, isn't it?

Prof. Quirijn de Mast: Absolutely, yes. We also had a third group in our study, and then we made use of a traditional fermented beverage that's commonly consumed in this Kilimanjaro region.

This drink is called Mbege, that's the local language, also commonly referred to as banana beer. And it's a beverage made of bananas. So they kind of mash bananas to make banana juice, and then they add some millet. And then this is fermented by some local producers. And then people typically drink sometimes half a liter, or a liter a day.

So in our third group, we had men with a Western-type diet, and we gave them this fermented banana beverage for one week. 

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Prof. Tim Spector: Did you try it yourself?

Prof. Quirijn de Mast: I tried. 

Prof. Tim Spector: It's quite sour, isn't it? 

Prof. Quirijn de Mast: It's very sour. Yeah. Yeah. So you really have to get used to the taste. 

Jonathan Wolf: And is it as alcoholic as a beer? 

Prof. Quirijn de Mast: Yes, it is. It has low alcohol content, so it depends on the time of the day that you drink it, because it gets stronger during the day, because the fermentation is ongoing. 

Jonathan Wolf: So, how alcoholic in the morning and how… 

Prof. Quirijn de Mast: So it varies, but usually in the morning it's about 1%, but it can increase to up to 3%.

Jonathan Wolf: So in the morning, that doesn't sound very alcoholic, you're not going to have a lot of hit. At 3% in your drink, a liter, you're going to feel that.

Prof. Tim Spector: It might make you sleepy in the afternoon or evening. 

Jonathan Wolf: And it sounds like you're not really selling it, that it's going to take over my local wine bar from the taste.

Prof. Quirijn de Mast: People say, well, it depends on the local producer. Some are well known to make it also more sweet. So it depends on your producer. But yeah, for me, when I've tasted it several times, it's pretty sour. 

Jonathan Wolf: Well, I want to find out what it does for me, and then we'll be figuring out how to source a tasty version. 

So Quirijn, I think you set up, sort of described this study with these three arms; the people halfway up Kilimanjaro switching to a Western diet. The people in the city who've been eating a Western diet for a long time, now switching back to that traditional diet, and then a third version where you're saying they're on a Western diet, but you reintroduce this fermented beverage.

I guess you're basically giving away free beer each day.

Prof. Quirijn de Mast: Yes. 

Jonathan Wolf: What did you discover? 

Prof. Quirijn de Mast: So, in the people with a traditional diet who we switched to a Western type diet, we basically saw that they developed more inflammation. That's the main finding. Within two weeks. 

So we looked at several aspects of the immune system. So, if we looked at the circulating immune cells in the blood, we saw that they became more activated. Also, they started to produce more inflammatory proteins in the blood. And third, we isolated the immune cells from the blood, and we stimulated these immune cells, so in the lab with microbes.

And what we noticed is that these immune cells performed less well. So on the one hand, they developed inflammation, but on the other hand, if you stimulate the immune cells with microbes, you see a poor response. 

Jonathan Wolf: And Quirijn, these are bad microbes you're talking about.  

Prof. Quirijn de Mast: Bad microorganisms.

Prof. Tim Spector: Salmonella …

Prof. Quirijn de Mast: Yeah. Salmonella, for example, and the tuberculosis bacteria, 

Jonathan Wolf: Two weeks on the Western diet. You gave them tuberculosis, and they didn't deal with it as well. 

Prof. Quirijn de Mast: Yeah. This shows that there is kind of an immune disbalance. On the one hand, the immune system produces too much inflammation.

Prof. Tim Spector: So it's ramped up really. So it's getting excited in a general way. But it's not very effective when you actually give it a real villain to attack. 

Prof. Quirijn de Mast: Precisely. So the switch to a Western diet had quite some negative effects on the immune system, basically.

While in the people that we switched from a Western diet to a traditional diet, we saw the opposite. So we saw a clear reduction in inflammation, which is good. 

In the third group, the people with a fermented banana beverage, it also had mainly an anti-inflammatory, so an inflammation-inhibiting effect. And we saw that the immune system was much more in balance. 

So these were the main findings. 

Prof. Tim Spector: And could you separate out whether this is a bad effect of the Western diet or the lack of good effect of the African diet? How do you separate those in your mind? 

Prof. Quirijn de Mast: It's hard to separate, but I think it's certainly both.

Prof. Tim Spector: Right. So if people had carried on eating their African diet, they might have been able to tolerate a little bit of Western diet, and sort of vice versa.

Prof. Quirijn de Mast: Yes. 

Jonathan Wolf: And with the banana beverage alone, is that enough to solve everything, or was that not as good as the people who moved on to the full African diet?

Prof. Quirijn de Mast: Well, you do see some different effects. The banana beverage could correct some, but I think there were additional effects of the switch to the traditional diet. So the combination would be perfect. 

Prof. Tim Spector: And in fact, it's interesting, our colleague, Christopher Gardner, did a study at Stanford where they compared, in Americans, high fiber diets against high fermented food diets, and they found different immune profiles of the two.

So there are different processes involved. Both are beneficial, but certainly the fermented food has a big impact of its own, and that's certainly something. 

We've done some studies in ZOE as well with our citizen science. People having extra fermented foods do get benefits that look as if they're different to the ones just by increasing your fiber intake or your plants.

So lots of different mechanisms are being brought into play. 

Jonathan Wolf: What are your thoughts on this study and the rather amazing results after just two weeks? 

Prof. Tim Spector: I don't like to ever read too much into one study, but it is actually backing up a few older studies that weren't as sophisticated, that did something similar.

So, where they've swapped some African for some American diets, and just looked very crudely, their microbiome. And that improved when they went onto the African diet and got worse on the American diet. 

And of course, this Stanford study, where they compared fermented foods and fiber. 

So it is very consistent and I think it is really exciting that we're seeing that we're now getting a new idea of the mechanisms of why foods are good for you. 

It's not about the calories, it's not about the fats, it's not about the vitamins, it's about their interaction with the gut microbes in our immune system and how that is so crucial to nearly everything in our health. 

If we can get that balance right, then you know, we can actually start to control these diseases that we've let go rampant.

And I think this is the really important message from these kinds of studies about learning these new mechanisms. And as you said, it's not just about ramping the immune system up, it's getting the right balance so that on the standard American diet, our immune systems are just going crazy, attacking everything, but they're not very effective.

So we're getting more infections, and the body's being confused by all these immune signals and not repairing damage, leading to all kinds of metabolic problems.

We need to learn from these studies and learn what the best foods are to eat so we can help ourselves. 

Jonathan Wolf: Can the two of you help me to understand the link between this immune system response that you were measuring and the impact on people's long-term health?

You were talking about obesity and diabetes and heart disease, and all these things that we know we are likely to die of in the West. You know, we're not very likely to die of an infectious disease anymore. 

How is that linked to sort of this immune system that you were measuring, because it's not immediately clear to me. 

Prof. Quirijn de Mast: So we know that inflammation is key to many diseases indeed, like cardiovascular disease, cancer, dementia, you name it. 

On the other hand, what we are more and more starting to understand is that if you have a chronic inflammation…

Jonathan Wolf: When you say chronic inflammation, what does that mean?

Prof. Quirijn de Mast: Chronic inflammation is that your immune system is chronically activated. So, yeah, that's basically chronically…

Prof. Tim Spector: …long term. It's quite normal to have an immune system that every now and again, pops up because it sees a threat, but it goes back to its normal levels. 

What we're seeing now in western populations on these bad diets are levels where it's continually being triggered.

It's like your fire alarms going off all the time, not just the weekly test; it's on all the time. So the body can't focus, it can't concentrate because it's just got all these alarm signals. It doesn't know where to go and repair things. It doesn't know how to efficiently attack some microbe, and we think this then disrupts metabolism, our mitochondria, and affects all kinds of diseases. 

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Because the body's just running really inefficiently. I think that's the way to think about it. It's like you're just putting the wrong petrol in your car, and so it can never really function properly when the whole system is just ramped up.

It's just like you're revving the car too much. 

Jonathan Wolf: I love that analogy of the wrong petrol in the car. I suddenly think I'm getting it. 

On the one hand, that sounds very depressing if you've been on the Western diet your entire life, like me. On the other hand, I think you're saying that in just two weeks, switching to this African diet, you could really see a measurable improvement.

Was that meaningful? 

Prof. Quirijn de Mast: I think it's meaningful. So it shows that, even after a few days, you can already see changes in your immune system. And that's what we also know from earlier studies, to be honest. 

So we know that it doesn't take very long to see effects if you change your diet. 

Jonathan Wolf: I think it's amazing. 

Before we switch on to what can this mean for listeners? Are you able to understand what the components of the diet are that are affecting the body? 

So you switch this whole diet for one group, another group are just given this banana beer. 

Do we understand at all, you know, what's going on, what parts of the what? What are the characteristics, I guess, of this African diet that are being so much healthier? 

Prof. Quirijn de Mast: Yeah, I think it's the combination. So it's not just one type of food that did the magic trick. So it must be the combination. 

So I think the foods that were. Important in the traditional diet, it's the traditional grains which contain lots of fibers, but also the legumes, which are fiber-rich, and traditional vegetables that we're eating. 

Lots of fruits contain anti-inflammatory products called polyphenols. Also, the fermented products they used, so they contain some live microbes who could have beneficial effects on the gut microbiome.

So I think it's the combination. 

Prof. Tim Spector: I remember when I was, spent some time with the Hadza tribe, which is just about six hours from where your experiment was. They had a lot of these berries, and that was a big part of their diet, these tiny little berries, which are the precursors of many of our cultivated berries.

And they had something like a thousand times the levels of polyphenols that ours do. And the other thing they were eating, the Hadza were digging up tubers. Which we'd now know ais things like yams, a bit like these root vegetables, potatoes, but actually they're much more nutritious than potatoes.

Was that part of their diet in this group of Tanzanians? 

Prof. Quirijn de Mast: So we didn't give them berries, but we gave them indeed roots and tubers, cassava, taro. So, absolutely, there's some variants, which is an important part of the regular, traditional diet.

Prof. Tim Spector: And Baobab was that…?.

Prof. Quirijn de Mast: No, in this region there are not too many Baobabs, so Baobab fruits were not part of this. 

Prof. Tim Spector: They cut down the trees, unfortunately. So they don't have them. But yeah, that was their porridge that the Hadza had as their daily porridge was the Baobab, which is interesting. 

But yeah, this porridge seems to be the binding thing across Africa, that it's a very, really easy way to get the fiber into your body quickly.

Jonathan Wolf: I think of a porridge as something, or an oatmeal as something that I get in a packet that I rip the top open, I pour into a bowl. I put in some milk, and I put it in the microwave for a minute and a half. 

I have a feeling you're describing a slightly different porridge. How do you make this porridge?

Prof. Quirijn de Mast: So the porridge most commonly consumed is Ugali. It's traditionally made from unrefined maize, and they add some water and they boil it. And then you get this kind of stiff porridge. 

But you do have variants. So in our study we also, as breakfast, we served participants a porridge made of millet, for example.

So you just use millet, you add water, and you boil it, and you make it into a porridge. 

Jonathan Wolf: So it's almost like making rice or a sort of sticky rice, and you just keeping the liquid in it. I'm imagining as soon as you say porridge, oatmeal that I'm adding sort of dairy milk. 

But actually it's just really sort of boiled to break it down.

Prof. Tim Spector: Yes, it's the grain plus water, and a bit of heat, or a lot of stirring. The Hadza didn't have a lot of boiled water, so you know, they would just add normal water to crush bits of the baobab into these little cubes. And basically, with 10 minutes of just beating it up, it would just become this creamy, thick liquid.

And I think this is the general way that, for millennia, we've been consuming these foods, which we've sort of forgotten.

Your type of porridge, Jonathan, is highly refined. They've stripped off anything on the outside that would stop it becoming instantly absorbed into your body. All those good bits have been thrown away.

You're just left with a very sugary center bit that dissolves instantly in the water or microwaves away, and then goes straight to produce sugar in your system. Whereas these old ones have got all that coating there. That is part of all these, what we're now discovering are the crucial bits.

Jonathan Wolf: That's really interesting. We did a podcast on oatmeal where we actually got to do a live experiment looking at what was happening to our blood sugar as we were eating these different sorts of oatmeals. 

I feel here you're describing something which is a whole level, both more nutritious but also less processed than any sort of oatmeal.

Forget about the stone-ground version. This is sort of more fibrous to start with. It sounds like a grain, which in itself is probably closer to its original form in nature, I guess, than the sort of oats and grains that we typically eat in the West. 

Prof. Quirijn de Mast: If I may add. Jonathan, what's worrisome is that more and more people are making these porridges from imported, refined maize, for example.

So Africa is important. Lots of staples nowadays, refined maize, wheat, rice, it's cheaper. So their local agriculture, indeed, it's transitioning more and more to mono crops, and also cash crops for exports. So, tea, coffee production.

Lots of this maze nowadays is being imported. 

Prof. Tim Spector: Because countries like the U.S. have an excess of maize, and they get subsidies from the government to produce it really cheaply. They end up dumping it in third-world countries where it overtakes the traditional types of grain. 

The local farmers, you know, who are growing it, can't compete. And so they're sort of being forced to transition into these less healthy grains that they're not traditionally used to cooking with anyway, and have all these health disadvantages. 

So yeah, it's a real sort of geopolitical problem at the moment. And when there are famines, it happens even more. 

Prof. Quirijn de Mast: Yeah. So there was a very, yeah, rich tradition of small-scale subsistence farming, but it's really declining nowadays.

Jonathan Wolf: So you're seeing this big transformation, it sounds like just literally over the 20 years that you've been visiting from this very traditional diet to a diet that looks rather similar to the one that I might be eating from my local supermarket. 

Prof. Quirijn de Mast: Correct, yes. 

Jonathan Wolf: So I think the results of the study are amazing. I think the fact that you can see an impact just in two weeks is fascinating. And I know that Tim is incredibly excited by your fermented test as well. 

Prof. Tim Spector: Yeah, definitely want to try that one. 

Jonathan Wolf: He's the world's biggest promoter of more fermented food. 

I would love to now sort of try and transition into actionable advice for our listeners. They're not living in Africa, this is not probably their traditional diet for the vast majority of people are listening. 

So I'm really interested, maybe just start by. Just describing a little bit more like what you might eat in a day on a traditional African diet. 

Then I'd like to start to talk about what could that mean for someone listening and how could they try and get the benefits from this, given the reality of what you might get from your local supermarket?

Prof. Quirijn de Mast: So what could we learn from their diets? I think point 1 is the biodiversity? 

I think Africa, they have thousands and thousands of very interesting edible plants. Many of them are still underutilized. We don't know their health effects yet. I mean, there's so much we can still learn, diet wise from all the indigenous knowledge from Africa.

So I already mentioned these traditional grains. I think they're very interesting. One of these traditional grains teff, it's more and more being used here and also claim to be one of the so-called superfoods. 

Jonathan Wolf: And how do you spell teff? 

Prof. Quirijn de Mast: Teff, T-E-F-F. 

Prof. Tim Spector: So it's an ancient grain coming from Ethiopia, which is supposed to be one of the precursors to wheat and what we're currently having as our main grains.

And you can get teff flour here now. You can make breads with it, and with einkorn as another ancient grain that I think you also see in Africa, don't you as well? 

Prof. Quirijn de Mast: Yes. 

Prof. Tim Spector: So, going back to these ancient grains, rather than this highly evolved wheat that we currently have in its current form.

Going back many generations could actually help us. You know, even just making bread in better ways. 

Prof. Quirijn de Mast: Yeah. So in Ethiopia, they ferment actually, the teff and make it into a kind of a bread. It's called injera. And that's the main staple.

It's also, it's gluten-free and as I said, contains a lot of fiber, a lot of polyphenols.

So that's one thing, the traditional grains. But also, I think there are some green leafy vegetables, which are interesting. An example that's commonly being consumed in Tanzania, it looks like a spinach, it's called amaranth. It's also sometimes called or referred to as African spinach.

And last, it's the fermented products. Although there are of course, important challenges. I mean, if you would like to consume a banana beverage that we used in our study, it's difficult with all the regulations that we have. 

Because here it should be pasteurized, and then you kill a lot of the microbes that are in these fermented beverages. 

Prof. Tim Spector: But the example might be kombuchas, other things that we do have in the West that could have similar advantages. If they have many yeast and microbes in.

Did you do any microbiome testing of the beer?

Prof. Quirijn de Mast: Yeah, we know from earlier studies, from literature. So indeed, it contains a lot of lactobacillus and saccharomyces cerevisiae, which is kind of a good yeast, a healthy yeast. So it's important for your gut microbiome. 

That said, I think if we look, we have some earlier data from the microbiome of people in this region. And what was very interesting is, in people consuming this traditional diet, we found some yeast in their microbiome. 

Yeast, their role is really underestimated in the role in gut health. Only a very small percentage of the microbes in our gut microbiome are yeast.

But yeast have such a strong immune-modulating effects. With our current industrialized diets, the loss of yeast in our microbiome could have strong health effects. 

Prof. Tim Spector: In many countries, doctors are trying to eliminate yeast from people's guts, because it's got a bad name. So the candida. Many specialists say, Oh, it's all down to having too much yeast in your gut. 

And what we're hearing, the latest research is saying the opposite is true. You need more yeast in your guts to give you really good immune benefits. 

Jonathan Wolf: Having yeast in my gut could be a good thing?

Prof. Tim Spector: Absolutely, yes. All the evidence is pointing in that direction.

There are a few rare exceptions where you get yeast overgrowth, but for the vast majority of time, we want to have more yeast. We want to stop killing them, and we want to be eating foods that introduce them into our guts. 

We don't know enough about them, but we think they have a crucial role for our immune health and dampening down inflammation.

Jonathan Wolf: So this fascinating thing we come back to on this podcast a lot where maybe originally with good intentions, we've ended up eating something completely different from the diet that we sort of evolved with. And then we're having these terrible side effects is how I understand this. 

But you can see within sort of two weeks from switching back to a more traditional diet or away from the traditional diet towards our new sort of industrialized, big food-driven. 

Prof. Tim Spector: Yeah. And you’ve got to realize that we've also lost a lot of our microbes. Because we all originated from Tanzania or Kenya, that bit of East Africa. 

When you look at those indigenous populations, they have twice as many species as we do in the West. That includes the yeast, and other parasites, as well as the regular microbes. 

So we've lost a lot. We need to learn again, to relearn how to regain them and how to keep them happy. 

Jonathan Wolf: So, maybe Tim, you can share what a listener might be able to do, if they're saying, I would like to eat more in line with the African diet.

To maybe take me through some easy swaps, listening to this, that you might be able to make, starting with where somebody may be today. 

Prof. Tim Spector: Yeah. Well, I think the first lesson is you've got to increase your fiber intake.

In this study, we compared 30 grams a day, which is the recommended level, you know, up to 90 grams. So we need to go beyond the recommended levels of fiber in the West. 

Jonathan Wolf: And can you give some examples of what that might mean for somebody, maybe eating the traditional, very meat-heavy, processed food diet? 

Prof. Tim Spector: The more meat you've got on your plate, the harder it is to increase your fiber because there's no fiber in meat dishes. So if you're just having dairy and meat, you're getting no fiber at all. 

So, reducing that and upping your level of high fiber vegetables is what you need to be doing. And in Africa, they have a lot of legumes, and that's the easiest way to get both protein and fiber. 

So legumes are beans, they're lentils. There's hundreds of varieties of these plants that we don't eat nearly as much of as we should be.

They're all pretty much good for you. Getting a mixture of them is great. 

Jonathan Wolf: We've been talking about some grains that are quite exotic to most of us in terms of what we buy from the supermarket. 

If I was instead eating different sorts of beans or chickpeas or lentils or things that are more familiar, in terms of being able to get them in tins from the supermarket, are they likely to have similar effects. Or are they likely to be much less effective than this African diet that we're talking about. 

Prof. Tim Spector: No, I think they should be pretty much as effective. 

What we also need to realize is that Africans have their own gut microbiome. Each population has their own specific microbiome. Remember, we only share less than 20% of our microbes with each other, in every country. We're going to share it less with someone in another country.

So, we mustn't assume that what works perfectly in one population will work for everyone else, but we can take some general principles.

I think that's really important, and realize that it's also personalized. But aside, I think we can take some broad principles here, see which ones do cross country-wide borders and use those examples.

So fiber seems to work everywhere. How you get it, may depend on what's good in your country and how your microbes get on with them. 

Prof. Quirijn de Mast: There is a clear seasonal effect on what people eat. So it really depends on harvest time, availability of fresh products. For example, fresh crops. So people change their diet throughout a year. 

Jonathan Wolf: Which is so different from my experience, which is even through my life, I remember as a kid feeling that the fruits and vegetables in the supermarket changed through the year. 

Now, actually, whatever you want, strawberries, asparagus, it's there all year round. It's just flown from some different part of the world. 

Prof. Tim Spector: That's true in the U.K. and it's true in the U.S. and other similar countries, but if you go to the Southern Mediterranean, it is very seasonal. 

They have certain fruits that they only have in winter, your apples, and your pears. They will have, you know, the peaches and other things, but you wouldn't get them out of season. And they don't eat them out of season. 

Jonathan Wolf: That might support more diversity of microbes because I'm having these different things that my different bugs might like.  

Prof. Tim Spector: Exactly. You're not having the same fruit every single week of the year. 

Prof. Quirijn de Mast: So what's interesting, Jonathan, in an earlier study in Tanzania, we found this very clear seasonal effect also of the function of the immune system, and of inflammation.

We could relay that to the products that people would eat after the wet season and after the dry season. So when you have the fresh products, then we would see that the immune system, the inflammation would go down. So you wouldn't expect that in an area so close to the equator.

Jonathan Wolf: As they're changing their diet, and particularly when they're eating more fresh produce, you actually see that their inflammation decreases and their immune system is sort of working better. 

Prof. Quirijn de Mast: Yeah. So after harvest, when they have all these fresh products and fresh vegetables, we saw a reduction in inflammation.

Prof. Tim Spector: And that could be due to things like the polyphenols being at their highest level in the really fresh produce, when they're really bright and they've got all the defense chemicals in there. 

The longer you leave them, the more you lose those defense chemicals. So we don't yet know the answer. This is speculation, but it is really fascinating, these observations. 

Jonathan Wolf: You've mentioned polyphenols quite a lot, but can you remind our listeners what they are, and why they might be declining after I take this plant from the field? 

Prof. Tim Spector: Well, polyphenols used to be called antioxidants, but they're chemicals within the plant that are there to keep it safe from damage, from sun, from wind, and also predators.

And it turns out that when we eat these plants, we ingest them and they act as fuel for our gut microbes. They can process them and then convert them into energy, and they use it to then replicate.

It turns out that the effects on the body are really via the gut microbes. There's very few effects that direct, so the gut microbes are there to break them down. So they're keenly sensitive to the levels in them. 

And we know we did a podcast, if you remember, Jonathan on olive oil and know that as soon as that olive oil is made, the polyphenol count is at its highest. So really quite bitter, makes you cough, really strong flavors. But if you leave it. A year or two, it's only down to half the levels.

So we know there's a general dropping off in the chemicals. They just like to be there on the living plant, and then they decrease. Same with wine. 

So you really want to be having… the fresher the vegetables, the higher the polyphenol count. And that's generally true. 

So these stored ones are made in factories, so that's why most commercially produced foods have very little polyphenols in them unless they've added them back in. 

Jonathan Wolf: Imagine somebody's listening to this and said, I'm going to try this tomorrow. I'm going to try and make my own version of your study, switching towards this traditional African diet, adding in all of these different foods that are going to give them much more fiber, and polyphenol, and all the rest of it.

You were able to measure a change in two weeks. Could they expect to see or feel any results at home if they did this? 

Prof. Quirijn de Mast: Yeah, I think so. So I think they can feel a difference in, for example, the bowel habits, with increased fiber intake. But maybe people will also start feeling more fit after a short time. 

Jonathan Wolf: And how have you changed your diet? 

Prof. Quirijn de Mast: I get that question quite often. Well, unfortunately, I haven't started yet, brewing my own banana beer at home. 

But how I changed my diet is, I clearly increased my intake of vegetables, tried to eat more legumes, have more lentils, reduced meat intake, limit processed foods. 

I was quite surprised. I expected these effects that we observed in these studies. So I mean, I work as an internist. I knew of course, the importance of what you eat, but that the effects are so pronounced. I hadn't expected, to be honest. 

Jonathan Wolf: Final question, Quirijn. Let's imagine that our listener finishes this episode and they immediately call their friend to share just one thing, which is the most impactful thing from your research that could help them improve their health. 

What would you want that one thing to be?

Prof. Quirijn de Mast: I think what we've seen in Africa, and what it learns us is the importance of switching your Western type diet to a whole food, plant-based diet. 

It has such a clear health benefit. So that will be my take and my message from this study.

You see, across Africa, meat intake has really increased in recent times, but traditionally, I mean, they didn't eat that much meat.

Jonathan Wolf: I would like to try and do a quick summary. 

The first thing that pops up to mind is that for your research, what you did is you built a pop-up restaurant halfway up Kilimanjaro, which is the most entertaining study I think we've ever had on the podcast, in order to understand how the traditional African diet works.

What you found is that switching to it in just two weeks can transform the way that your immune system works, such that it's much better if you move away from a traditional Western diet.

On the other hand, rather depressingly, you could be on this traditional African diet for 20 years, and just two weeks on this highly processed Western diet, suddenly, you test what happens if you come into contact with something like tuberculosis, and your immune system is working much less well.

So that's really extraordinary. And the other thing I took away is that the sorts of diets that people are eating in Africa has transformed in the 20 years that you've been visiting.

Actually, many people are now eating exactly the same sort of highly processed food that we're all eating in America or Britain. And with that, you've seen this explosion of diabetes, obesity, and heart disease. 

There isn't just this one good diet like the Mediterranean diet. There's probably a set of these traditional diets, but they have a lot of things in common. 

The key things, I guess, that I took away from this, is that they have a very big variety.

And Tim, you said your microbes are fussy, so you need to have a wide variety of different fibers to feed all of these different microbes. Your African diet has all of those different plants, many of which we just have sort of lost in the diets that we have today.

But also interestingly, you did a specific test around fermented drink, this Mbege, the banana beer, and you found that even if you were still on the Western diet and you just added that, it had a really beneficial impact. 

So again, something that's come up quite a few times on the podcast with completely different sorts of fermented foods is that it has this really beneficial impact.

You talked about polyphenols. So it's not just the fiber in the food or the diversity, it's also these polyphenols. These defense chemicals.

What you saw was that when the diet is fresher, so these have been harvested more recently, actually that lowers your inflammation, and improves your immune system.

In terms of what you could do, one takeaway is I want to go and try and see if I can source teff. This ancient grain that apparently, I could find quite possibly in my supermarket as an alternative to wheat, that I could try for baking.

But also in a simpler way, I don't need to eat these very specific millets and things that might be unfamiliar. Actually, beans, chickpeas, lentils, all of these things that I can find in a tin in my supermarket, if I were to use a lot more of those, I can get much closer to this African diet, but with food that's familiar. 

I think what I heard is you think I could have the same benefits that you saw in this study, halfway up Kilimanjaro.

Prof. Quirijn de Mast: Correct, yes. Fully agree.