Torwen:
Hello. And welcome to the Ideal Nutrition podcast. My name is Torwen Eerkins, and I’m here with my co-host Aidan Muir. Today, we’re discussing the role of polyphenols in gut health. To start off with a little background, what actually are polyphenols? Polyphenols are compounds that plants produce.
They’re not vitamins, minerals, or fibre. But, they’re what we call secondary plant metabolites. There are about 10,000 of these. And plants make them for their own reasons. That can include things like UV protection, keeping insects away, etc. They’re typically classified as flavonoids or non-flavonoids.
And flavonoids are the largest group, found in most colourful fruit and veg. They contain things like flavones, flavonols, isoflavones, and anthocyanins. Whereas non-flavonoids include things like phenolic acid, lignans, and stilbenes.
Aidan:
Talking about bioavailability now, bioavailability is often low. But it can be hugely variable. Some get absorbed less than 1%, while others can be 50% or higher. There are things we can do to adjust that absorption a little bit. For example, having it alongside dietary fat can increase it.
A common example is having olive oil with vegetables. But most absorption occurs in the large intestine. Gut bacteria often break these polyphenols down into smaller metabolites. And absorption can differ based on your own personal microbiome, partly due to that too.
Torwen:
They can play a fair few roles in the body. Mainly, this is because they act as powerful antioxidants and anti-inflammatory agents. They can protect cells against damage. They reduce chronic disease risk. And they may promote heart health, gut health, and brain health. But as we said, today we’re focusing on the gut health benefits specifically.
Aidan:
And they can affect gut health through a variety of means. The first one I’m going to start with is prebiotic benefits. Since many polyphenols reach the large intestine intact, they can act as food for the bacteria there. This can increase the growth of certain beneficial bacteria. The most common ones we’d be talking about are Lactobacillus and Bifidobacteria. And it’s similar to fibre in this way, just with a slightly different mechanism.
Torwen:
And that shift is often associated with improved microbial diversity. It is also associated with reduced markers of gut inflammation. One downstream effect of this microbial shift is often butyrate production.
Butyrate is a short-chain fatty acid. When gut bacteria ferment certain substrates, it acts as a primary fuel source. Bacterial strains, like Bifidobacterium or Lactobacillus, produce more butyrate. Butyrate does a lot in the body. It has those anti-inflammatory properties. It helps with colon cell integrity. And it can also help with regulating immune function and so on.
Aidan:
I was looking at research on this because I’m always curious. How much does this matter? It is one of those things that sounds really good in theory. But I’m like, how much does this matter?
So I did look at a systematic review, which I put in the show notes. It found there is heaps of animal research supporting this quite strongly. It clearly does do this, but there still isn’t that much human research. What we have in humans looks very promising. We have one huge confounding variable.
A lot of these polyphenols are found in plant-based foods. In many cases, they’re also high in fibre. So if you’re measuring someone with a high polyphenol intake, you’re probably measuring a high fibre intake. That could cause all of these prebiotic benefits. It could also cause an increase in butyrate in many cases.
Torwen:
Which makes a lot of sense. Another way polyphenols can help is anti-inflammatory signalling. They have direct anti-inflammatory effects. This mainly occurs through the inhibition of a pathway that we call NF-kB. It is essentially a master regulator of inflammatory gene expression in the body.
When this pathway is chronically activated, it may be associated with low-grade chronic inflammation. This can underpin a huge range of conditions. So lowering the inflammation in this pathway can be beneficial.
Aidan:
And we do have heaps of human randomised controlled trials on that one too. That is exciting. We see measurable increases in things like CRP, IL-6, and TNF-alpha. The effect sizes are often not huge, but they are relevant as well.
And the final thing we’re going to talk about with the benefits is gut barrier integrity. Polyphenols appear to upregulate proteins that reduce intestinal permeability. Other people call that leaky gut. So it helps with addressing that. This is relevant to conditions like IBS and IBD. Once again, it’s another area where there is a lot of indirect evidence.
However, there is not a lot of strong evidence. It’s not like we’re looking at research on whether polyphenols dramatically improve symptoms in IBS. We haven’t really seen anything on that. But indirectly, a lot of this stuff looks positive.
Torwen:
And again, when you’re looking at overall diet quality, you’re indirectly increasing polyphenol intake as well. Cool. Should we move on to chatting about some food sources then?
Aidan:
Sure thing.
Torwen:
When we’re talking about polyphenols, a lot of the time we’re talking about colourful fruit and veg. Like we said, this could include things like berries. It also includes dark chocolate, extra virgin olive oil, and green tea. It could be things like legumes, red onions, cloves, star anise, and turmeric.
Aidan:
Yeah, and in many cases, we can measure improvements even just from individual ones. If we’re looking at blueberries, we see anthocyanins potentially being responsible for improved cognitive function. If we look at dark chocolate and other things, we can see measurable improvements. In some cases, I think aiming for a variety of polyphenol-rich foods makes sense.
And in other cases, if you’re looking for one specific benefit, you can double down on one as well. When we go back to bioavailability, different approaches from cooking and storage can impact it. We can list examples. I’m assuming you’ve got examples. We’ll go back and forth. I’m going to start off with one. Cooking tomatoes can increase the bioavailability of phenolic compounds.
Torwen:
Yes. I’ve got something like fermentation, which is a bit of an interesting one. Kimchi, kefir, sourdough, and that sort of thing can also increase bioavailability. They do this by pre-converting polyphenols into a more absorbable form.
Aidan:
Frozen berries retain polyphenols well. But if you cook with them, that can cause losses of these polyphenols.
Torwen:
That’s the last one that I’ve got as well. There are some heat-sensitive things, like potentially flavonoids. When cooked, this can reduce the polyphenol content. It makes sense to consider things like fresh or frozen vegetables if you’re storing them long term.
Aidan:
Absolutely. The last one on my list was olive oil. So it’s heat-stable to a point. Extra virgin olive oil is way higher in polyphenols than regular olive oil. The polyphenols often do hold up well under heat to a certain extent. But there is a bit of a reduction. And the longer you go for, and the higher the heat exposure, the more reduction there is.
Torwen:
One thing Aidan mentioned earlier is how we can improve the absorption of polyphenols. One we most commonly talk about is the fact that fat can improve polyphenol absorption. Many polyphenols are fat-soluble. Eating them alongside a healthy fat, like extra virgin olive oil, helps with how much you can absorb.
This is potentially one reason why the Mediterranean diet works well as a dietary pattern. We’re looking at things like vegetables served with olive oil. Or often, pairing spices with things like fatty foods or fatty fish works well.
Aidan:
Another, and I’d say the most well-known example, is that curcumin technically is a polyphenol. We don’t often think of it in that category, but it is. Consuming it alongside black pepper massively improves absorption. It is not well absorbed at all without black pepper. It is noticeably better absorbed there too.
And the last one I had was vitamin C alongside polyphenols often improves absorption. But the practicality of this is pretty slim. Many polyphenol-rich foods already contain vitamin C. There are exceptions to that, of course. But in a lot of cases, this is going to take care of itself.
Torwen:
Practical recommendations for anyone that’s listening then. Should we go back and forth with these as well?
Aidan:
I only wrote one, so maybe you start.
Torwen:
Firstly, having that variety of polyphenols makes a difference. We often come back to that 30 plant foods a week. Of course, this isn’t perfect science. But I think having a variety makes sense. So if you want a bit of a number, 30 is often seen as quite large. But we do encapsulate things like spices and using that quite freely as well.
Aidan:
Yeah, that’s the main one that I had. It’s that diversity and also getting enough quantity. I think you can go out of your way to take certain steps to achieve these. For example, if you’re buying chocolate, and you’ve got dark chocolate. Go as far as you’re willing to go with the percentage of dark chocolate. Whether it’s 70% versus 80%, or 80% versus 85%. Most people draw a line somewhere.
Torwen:
I was going to say 70% is max.
Aidan:
But yeah, going with the higher percentage, if you can. Even little things like drinking green tea are such an easy win. One thing I like about nutrition is that, on one hand, I can just say, have a good diet. But I obviously read a lot of studies. There are so many times I’m reading a study, and I’m like, I should probably do that more.
Using green tea as an example, if you looked at green tea and cognitive function, there is an improvement. There are so many of these little things. If you do a little bit more of it, it probably improves outcomes in different areas of life.
Torwen:
For sure. Adding on to those little swaps, it might be something like normal olive oil. Or actually buying that extra virgin olive oil, if that’s a possibility for you. Adding more colourful fruit and veg throughout the day also makes sense. Especially on top of meals that you’re already having.
Aidan:
Absolutely. Well, we will wrap up there. That has been episode 257 of the Ideal Nutrition podcast. As always, if you have not left a rating and review, we would massively appreciate that