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#603: Should Dietary Fiber Be Considered Essential? – Andrew Reynolds, PhD
00:59:14
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- [00:00]
A
Hello and welcome to Sigma Nutrition Radio. This is episode 603 of the podcast. My name is Danny Lennon. You are very welcome to the show. Whether you are a longtime listener or maybe this is the first time you're listening in, you are very welcome. Today, of course, we have another discussion that gets deep into nutrition science and I'm going to be welcoming back a previous guest of the podcast who was on the show back in episode 498, where we discussed some of his excellent and important work in the area of carbohydrate quality and health. And that is Dr. Andrew Reynolds, who's an associate professor at the University of Otago in New Zealand. He has done some excellent and important work that relate to how diet interacts with chronic disease risk, such as in type 2 diabetes and cardiovascular disease. He's worked with both randomized control trials as well as with epidemiology, and more and more his work has been focused in the area of nutrition epidemiology. And indeed, in our previous discussion we discussed some of his very important work that has been used to inform evidence based dietary and clinical guidelines as well as policy from some of the biggest organizations in the world. And part of that was using the conjunction of both randomized controlled trials and prospective cohort studies in side by side analyses, something we will maybe discuss today as well. But recently Dr. Reynolds and his colleagues authored a comment piece in Nature Food titled Dietary Fiber as an Essential Nutrient, where they made a case as to why we should maybe start thinking of dietary fiber as an essential nutrient despite it not meeting the traditional criteria that's required for essentiality. And it gets into a range of really interesting concepts, not only how we might define essentiality, how fiber could meet those particular criteria, but whether those are the right criteria to judge it on anyway. And so we're going to get into much of what was discussed there, as well as the broader literature discussing dietary fiber, its impact on overall chronic disease risk and mortality, and anything along the way that we find interesting. So, as you will see, Dr. Reynolds is an absolute expert in this area, has an excellent way of articulating the research, and I really hope that you enjoy this discussion. If you are a Sigma Nutrition Premium subscriber, you will be getting a detailed set of study notes to accompany this episode, as well as a fully edited transcript. And you will also be getting our Key Idea segment that follows the interview over on the premium feed. If you're listening on the free public feed of the podcast and you're interested in getting more out of your podcast, Listening and want to use this as a resource for learning more about nutrition science. Then maybe check out our subscription, Sigma Nutrition Premium. With that, you get some of the benefits I've just mentioned, like our study notes for all the episodes, transcripts, key idea segments, as well as the ability to put questions to us, which we answer in Ask Me Anything episodes. And then each month you also get a premium exclusive episode that you can only listen to over on the premium feed of the podcast. So if that sounds like it might be interesting or you want to try that out, please check that out in the description box. It is the primary way that keeps this podcast running. So thank you so much for everyone who is a premium subscriber. It really makes a big difference and I very much appreciate it. So with all of that preamble out of the way, let's get into this discussion with Dr. Andrew Reynolds. Here we are. Dr. Andrew Reynolds, welcome back to the podcast. You are very welcome.
- [03:56]
B
Thanks, Danny. It's great to be back. It's been three years.
- [03:58]
A
Three years, indeed. I think, as we had been mentioning, time has flown by a bit too quick. We thought it was a lot more recent than that, but indeed, three years ago, for people listening, Dr. Reynolds was on the podcast. We talked all about the concept of carbohydrate quality and some of his excellent work in that area. That's episode 482. If anyone hasn't listened to that, I encourage maybe put that in your To Listen list and it'll be a really nice adjunct to what we're discussing today. Today, of course, we're going to get into another really interesting area that you've published some thoughts on recently that I want to dive into. But maybe very briefly, before we get to that, Andrew, can you maybe give people who are new to you a bit of an idea of your academic interests and your background?
- [04:43]
B
Yeah, absolutely. So I'm Andrew Reynolds. I'm an associate professor at the University of Otago, which is down at the bottom of New Zealand, which is down at the bottom of the world. And I kind of mainly call myself a nutrition epidemiologist in that I run randomized controlled trials looking at sort of dietary interventions relative to usual care, as well as doing meta analysis of the existing data from trials, data from prospective observational studies. And I do those meta analysis largely to inform dietary guidance. So that might be at a global level for the World Health Organization, but it's also at national levels for countries like Australia, and then to inform sort of clinical or position statements from groups like the Heart Foundation. Also the Diabetes Nutrition Study Group off the European association for the Study of Diabetes. Quite a long title, but a very cool group. So yeah, that's my work. Just an academic working hard trying to understand more about diet quality and how to improve that nutrition advice for individuals and for health professionals.
- [05:40]
A
Fantastic. And I won't wax lyrical about your work again because I've done that not only in our previous interview, but on other episodes as well. But I will leave some of those publications in the description box for people listening to go and check out. And recently off the back of publishing a comment in Nature Food titled Dietary Fiber as an Essential Nutrient, a title that will call attention to a lot of people, I'm sure. After you had let me know about that, I'd seen a number of researchers and academics in the field also post about this with a lot of intrigue and positivity. And so I want to work through some of your ideas in this and how it connects to dietary fiber in general. And they're for public health now, I suppose, as the kind of name of the piece alludes to, you make this case that dietary fiber should be considered an essential nutrient. So probably the best and obvious place to start is getting a correct definition for everyone of what we mean by essentiality in this case. And I suppose those classic criteria we talk about in terms of nutrients being essential or not.
- [06:43]
B
Yeah, absolutely. We've been so my me and my team have been talking about this for probably three plus years. Way before we did that initial podcast. When I went looking, I didn't find a soul body that had the concrete definition of an essential nutrient or a soul body or organization that had a list of these are the essential ones and these are not the essential ones. So that in itself was interesting. All of the main sort of caveats boiled down to that the body needed the nutrient to survive, so it had to have a physiological function that was recognized. The body couldn't produce enough of that product of itself to service its own needs, so it did have to come from things like diet. And then probably the more trickier one is that there had to be a certified or obvious deficiency state that could be reversed. So if you removed the nutrient, an illness occurred. So vitamin C and scurvy. And then when you returned the nutrient, the deficiency state went away. And that sort of framing makes a lot of sense for when most of the essential nutrients were discovered more than 50 years ago, where things like ethical concerns and trials weren't a problem. You could deprive people of nutrients and see what happened or there was natural situations such as the long sea voyages where people were without fruit and vegetables for months and months, where you'd naturally sort of observe deficiency states popping in for micronutrients. Those were the three sort of main criteria that we wanted to address. There's also a sub commentary in the article, I guess, on the fact that the definition of essentiality is a bit old. We don't really look at nutrition in terms of deficiency states anymore so much as we look at how to optimize our health. What are those sort of suggested dietary targets that give additional benefits beyond survival and increase our lifespan. But we did want to stick to those initial criteria, those three that I just mentioned, and address fiber in that context, but also recognize that destination is quite old.
- [08:31]
A
Yeah, I suppose that leads us to understand there's maybe two aspects that we need to work through here. One is that based on some of those criteria that have been previously put out, we would often get to that conclusion that while maybe fiber is important, the typical line was, well, fiber is non essential technically for some of these reasons, based on this criteria. And so I suppose, given that you are making a case that maybe we maybe need to rethink that, there's probably two places to look. One is like you say, have we maybe got it wrong in terms of that in that fiber actually does meet those criteria that you've just laid out and based on new evidence, it could actually meet all those. Or then the second part might be, even if it doesn't meet some of those older criteria, maybe we need to reconfigure how we think about those. Can you maybe just talk a bit more about your thinking of those two different kind of buckets, if that makes any sense.
- [09:24]
B
Yeah, absolutely. Makes perfect sense. So thinking about that, the sort of older established definition, the thing that fiber couldn't really show was the deficiency state. We had proof that the body does need it. We have proof that body can't produce it itself. But we didn't really have this affirmed. You know, a disease, a clinical condition where someone was diagnosed you with having inadequate fiber intake. And so that's where we went looking and where we were sort of thinking and looking for the last couple of years really was one of the more interesting parts of nutrition sites at the moment, which is a greater understanding of how the gut microbiome interacts with its host, us as humans. What we know is that the microbiome pretty much feeds off fiber as well as some of the secretions in their gastrointestinal tract. So that's their soul food. So it sort of has a very sense sense check. If you eat fiber, you have greater microbiome density, diversity and functionality. And people who have sort of low intakes of fiber don't tend to have those things. In fact, some of them slip into something called gut dysbiosis, which is a dysregulated environment where the beneficial bacteria aren't really present and producing what they should. And there's more likely a chance of sort of opportunistic pathogens and things in your gut causing you issues. So we sort of pitched it there, thinking, well, that is a deficiency state. If you could measure the gut microbiome and have a standard that said, you know, this is a bad one, a dysregulated one, you would have a deficiency state. And certainly the evidence of giving people fibers in that situation does show a reversal of effect. Probably not for all gut dysbiosis. There might be other causes of gut dysbiosis. Of course, it's a catch all sort of term for an unhappy microbiome. So there's going to be multiple causes there, but certainly for a lot of them, fibre restores it. So that's where we sort of pitched out deficiency state as a inadequate or dysregulated gut microbiome. With fibre being able to reverse that once it's restored in the diet.
- [11:17]
A
There's a few things that comes up there because obviously this is a incredibly complicated area of research, as I'm sure you are well aware. And first of all, if we think about that concept of can we define what that deficiency state looks like? And then second, is there a way to reverse that with this known nutrient? So if we take that first position, first of what that deficiency state looks like, you mentioned this kind of dysfunctional gut microbiome, and if we can get a definition of what that is or have some type of phenotype, then we have a result that we can show this is the outcome of that deficiency. And then we would need a second part then on reintroducing more dietary fiber, we can get a reversal of that state. Now, with this, there's a few challenges and I'd love to know your thoughts on how you kind of work through the literature or your current thinking on it. One that commonly comes up is this dynamic nature of the gut microbiome. So those changes can happen very quickly in response to increasing or decreasing certain nutrients, in this case fiber or the overall general diet. And then the second challenge seems to be defining which of those changes are True dysfunction or dysbiosis as you termed it, versus maybe some transient changes that we're not exactly sure. Can you maybe walk us through your thinking about how to overcome those challenges and what went into your kind of defining of those phenotypes?
- [12:44]
B
Yeah, for sure. I mean, my concerns in this area. Absolutely your concerns. We can easily elicit a transient change in gut microbiome with a lot of different things, dietary and other. But is it meaningful? Doesn't mean anything to people's health. So we didn't draw a line in the sand and say, you know, you must have X amount of bifidobacteria or Y amount, if anything else. We didn't think that was really our field. What we've done is put the idea out in the hope that it generates more sort of interest from our colleagues in microbiology, people who understand the dynamics and building blocks of what's going on down there better. At a clinical perspective, you might want a diagnostic test that would look at things like that. But at my level, I sort of discuss it in terms of microbiome density, so sufficient quantities, microbiome diversity. So all the types of micro gut microbiome that you would expect or hope to have in a fully functional gut as well as gut functionality or microbiome functionality. So that's. Are they producing the things that we expect them and want them to produce, like the short chain fatty acids. So at a very top level, that's all I deal with in the knowledge that people might come along and say, well, key aspects of the gut microbiome that, that relate to long term health are X. And therefore measuring that and understanding particular levels of activity would give us our hard line of what is gut dysbiosis at the moment. That knowledge doesn't exist. It's a whole lot more research, a lot more samples and understanding those long term effects, as you said, to get to that firm line. But we were still able to hypothesize and say, well, this is probably it. This is the issue that is restored with fiber and that is our deficiency state.
- [14:18]
A
And so I think one of the interesting things here is that it probably would end up coming down to that dysfunctional state or that dysbiosis being an umbrella for a whole host of things, which is maybe different to what we see with the deficiencies of other nutrients where clear deficiency, we have these symptoms or we have diagnosed scurvy. And it's a very kind of nice neat thing. Here we're getting into an area where a bit more complicated but nevertheless doesn't mean that it's impossible or that actually it can't be done. And so again, that's, I suppose, work to be done, but that's the case being put forth.
- [14:55]
B
Yeah. At the moment it does look complicated. And I did, yeah, draw to the fact that the gut dysbiosis is probably an umbrella term for multiple conditions. However, if you think about those long term sea voyages, they wouldn't have just been getting served scurvy after months and months. I see. They would have had multiple deficiencies, probably, and they would have presented in different cases. So same thing back then for the surgeon on the ship. They would be thinking, what am I dealing with if this looks so complex? Some of these people have teeth falling out and some of them have other things going on with them. At the moment it's sort of bare at that stage of history where we're thinking about, okay, we have a lot of things going on with a dysregulated gut microbiome, but the next steps of knowledge and science will draw out, well, which are the ones that relate to fiber and which are the ones that relate to other things.
- [15:38]
A
Really interesting. So maybe as we start working our way, we can take it a step back for people when we think of this whole fiber story and think of the typical guidance we see around dietary fiber. And depending on where people are, there'll be slightly different figures. But on average, those typical daily recommendations come in relatively similar from country guidelines to country guidelines. One of the interesting things I think we touched on in our last discussion was that we have this kind of quite strong evidence or incredibly strong evidence around those, let's say, high versus low comparisons in epidemiology that get us those kind of figures. However, there are still some interesting questions about dose response even beyond that that we can talk about. Can you maybe for the moment right now, give people an idea of when it comes to general dietary fiber recommendations? What are most of those guidelines typically based on what type of evidence and a sense of the strength of that evidence based, let's say, supporting our current recommendations.
- [16:43]
B
That's a really good question. Definitely my area of interest. So the, let's start with what are the recommendations for the who? Their global recommendation is that adults have at least 25 grams per day. Most nations echoed at least 25 grams or at least 30 grams. And then people with diabetes have a recommendation for at least 35 grams. So that's sort of where all the recommended amounts sit. Actual intakes probably range between 12 and 20 to 22 grams. As a country average. So some places like the United States of America and parts of Asia have quite low 1412 grams a day, not quite, or just at half the recommended amount. And then other countries have around 20 to 22. So these are some of the Northern European, Australia, New Zealand sort of countries where they do have more fiber, fiber, but they're still not quite there as a population average. So it's quite a good target because it is in line. If people had a, an effort to increase fiber intakes by say 5 grams a day, which is achievable, they would be hitting that at least the 25 gram sort of target to get there. So that's good to know. What is that number built on though is a really good question. So the evidence, and I will talk about the one from the World Health Organization, it looked at both prospective observational studies where people's lives had been tracked for decades and they looked at initial fibre intakes and then what happened to those people over those decades? Did they get heart disease, did they get type 2 diabetes and then did they die prematurely? Those observational studies were taken from all over the world and then meta analysed to look at combined effects. And then from the trials they also looked at trials where some people had been given fibre and other people hadn't been given fiber to look at the cardio metabolic risk factors. So the important markers in clinical care, such as cholesterol concentrations, measures of blood glucose or glycemia, body weight, blood pressure, and then they meta analyzed that data as well too to say what is the effects of increasing fiber intake? So looking at them side by side is really quite exciting because we didn't used to do that 10 plus years ago in evidence based recommendation building. But now there's more of a recognition that in nutrition we want trials because they have those cardiometabolic risk factors and not many trials go long enough to capture hard outcomes like heart disease or death. And then we want the observational data, those prospective studies where we follow people for decades to see what they get. So you look at those together or side by side, and then you look at them in terms of higher versus lower, as you said, but also looking for dose response across different cohorts. So you might have a cohort where intakes are 12 grams to 18 grams and then you might have a cohort that has 16 grams to 22 grams and then you might have a cohort that looks at 18 grams to 38 grams and you stitch the sort of evidence of what's happening to that disease across the whole spectrum of fiber intakes. And you look for either say an increase in risk reduction or an increase in risk for other nutrients to see if there's that consistent picture across the spectrum of intakes. So dose responses are really important consideration. That pattern in the data of a dose response can exist separate to any sort of influence or bias. If one of those studies was heavily biased by something, say they didn't adjust for other important factors, it would sort of get washed out in the overall effect. So when we see a dose response association, we're quite happy and excited because it's a really much stronger level of data than just looking at higher versus lower intakes, which only looks at the two extremes of intake. And you might think that people who have very low intakes of anything could be a little bit strange in other ways. And people who have very high intakes, if anything, could be a little bit strange in other ways. So higher versus lower associations not as strong. But when you see a dose response next to it increases our confidence. And then when you look at the trials of increasing intake and you see why the risk in say type 2 diabetes is there, or the risk reduction in type 2 diabetes is there, because it's improving measures of blood glucose control, you sort of build a picture from multiple data sets to increase confidence that this nutrient is really important for those outcomes. So that's what the World Health Organization evidence is based off. Countries do a national country, national level bodies do similar evidence synthesis for their own countries in their own dietary guidelines. And then you've got the sort of regional ones, such as those diabetes guidelines for the clinical management, dietary management of diabetes. In Europe they did their own separate processes to inform their recommendations. So ideally those guidelines come from the evidence base. Ideally it looks at both trials and observational studies and ideally they consider some of those advanced meta analytic techniques such as dose response.
- [21:24]
A
And I think this is an area where that triangulation of different study designs, different fields and different data sets is really crucial. Because when we have a question that nominally is about chronic intake over time and these risks of diseases, this is where a lot of those prospective cohort studies from epidemiology can really shine and maybe help us answer questions that we might not get necessarily in a trial. But then one of the real issues here, particularly with dietary fiber, relates to these intakes that you've already mentioned, that when you look at the populations, on average, most of them, virtually all of them, don't meet those typical recommendations that we already have. So in general, intakes are relatively low. So even doing those high versus low comparisons, we've often found that the quote unquote high group isn't necessarily super high. And so thinking of some of the cardiovascular disease work in the area where we were getting some of those recommendations for, let's say, 25 to 30 grams per day, coming from those high cohorts who are in around that figure, we can't really say if more would have been better from those particular studies because there wasn't a higher group to necessarily compare. And so this is where this, some of your work in particular has been really interesting of seeing. What do we get from those that perspective, cohort data, what do we see in actual trials looking at some of these other markers as opposed to actual disease outcomes per se, marrying that up and trying to come to some of these conclusions. And I think also here we have very. Another interesting thing about dietary fiber is we're concerned with multiple different outcomes, such as a cardiovascular disease. We know there's this really strong association, but we also know colorectal cancer has had this historic association reducing risk of type 2 diabetes. Can you maybe talk about how you go about trying to think about when we are coming to recommendations and we have all these different outcomes, we have all these kind of limitations depending on which type of evidence we're looking at. And bringing that together in the synthesis that you just measured, how do you even go about that in the first place?
- [23:34]
B
How do you draw a line to say 25 grams is the target? Yeah, it's a really good question. I would say that the most people want a quantitative target. They want a number. They want to understand where they are and where they need to get to. That's quite helpful advice to provide people when you have the data to support it. For fiber, when we had that signal where trials of increasing fiber showed benefit and the observational studies showed dose response response with all those health outcomes, as you mentioned, and it is weird that fiber affects all those health outcomes. We did wonder, well, where do you draw the line? Where do you say this is the amount? And essentially for the World Health Organization, we went back to the dose response curves because those curves could have been linear, with the more fiber, the greater the benefit, or there could have been some plateauing. So initially, from really low intakes to moderate intakes, you'd see this strong risk reduction. But then as they crept up into above 30 grams, you might see a plateauing effect. So the line sort of stilled, it became a bit flatter. So additional benefits beyond that for some of the disease outcomes weren't evident and a lot of the plateauing seemed to occur around the 25 gram point. I did do fancy statistics to sort of crunch that number for them. But at a basic level, you could look at the dose response curves across all the disease outcomes. And while some were linear and they did show improvements, some of them also plateaued. And so that's why the phrasing is at least 25 grams. If the population could move to 25 grams, you would see consistent benefits across all those outcomes with additional benefits of some outcomes beyond it.
- [25:05]
A
And I suppose that's a distinction that we will make, and I'm sure we'll revisit to a bit later, that there are two different things we can talk about. One is population guidelines or recommendations and advice we want to move people towards. And the second is for any one individual, what they necessarily want to do with their diet, for quote, unquote, maximal risk reduction across these different outcomes. One interesting debate that I've seen within this field of research between different people involved is when it comes to some of those dose response curves and that plateauing, that plateauing that we're seeing at some of those numbers that you've mentioned, how much confidence we have that is in those cases a true plateauing, or in other words, is it a plateauing that we're seeing from a lack of clear evidence or stronger evidence we would like to see that would help us inform this question of those dose response because it's very challenging to do for multiple reasons and we always would like more high quality research. And so there has been some of this debate, depending on the outcome we're talking about where this plateau truly actually lies, depending on the outcome. What's your kind of thoughts at this point on some of the dose response data we have available to us to try and answer that question?
- [26:20]
B
Yeah, really good. I can also throw in another potential issue with those plateaus in that it's just a statistical artifact. A lot of the dose response curves are drawn or generated with quite complicated things. I use restricted cubic spline models and they actually force the line through certain points along its journey. So it could actually just be that there's a knot or a force there at 25 where the line alters its shape. That's another consideration that people might consider when looking at is it a real dose response or is there a statistical artifact that's showing up there? I guess in fibers cases we had all those different disease outcomes, so we could look at the heart disease one relative to the diabetes One relative to the colorectal cancer, one relative to the all cause mortality one, the cancer mortality one and the cardiovascular disease mortality one. So we were looking across eight dose response curves to see if there was a similar pitch or change in a plateauing of effect. Not many other nutrients that consider one or two outcomes can do that. So that was certainly a strength of that process. I would also say that the Dietary Guidelines really should just has to be done on the best case evidence. You said yourself we always want more, we always want more higher quality. But in the meantime we still have to have dietary advice and so we have to pitch it and put it somewhere where we think is useful, achievable, aspirational, as well as intended to deliver meaningful health improvement. So if we were always waiting for the best quality evidence, we would have no guidance anywhere and we'd always just be funding more studies to try and get that perfect amount. Now, if in the future dietary guidelines shift to say that fibre should be had at 28 grams instead of 25 grams, that's fine. We're still getting people to move towards the higher intakes. And certainly with fibre we see the greatest benefits for very low consumers moving up to moderate intakes. So if we didn't get 25 grams exactly right, if it should be 26 or 28, we still did it on the best available evidence and it's still a helpful and meaningful target. Especially when you think about where most of the population health gain occurs, which is moving through very low to moderate. Yeah, critical answer to that question rather than a technical one.
- [28:29]
A
Yeah, and again, that is probably my tendency to look at some of these more academic interest, this question. But as you note, from a public health point of view to this point, we know the vast majority of people are nowhere even close to those current guidelines. So really, if that number would see a benefit at even higher intakes is a moot point for a lot of people. And the guidelines already allow for much higher intakes if an individual wishes. These are kind of get to this point and if you want more, that is fine. And so we'll come back to the public health implications a bit later on. One of the things that I know you touched on in your, in your comment, which I think is a really excellent point that maybe we can overlook when we start talking about general recommendations in terms of grams per day, because we're always talking about total fiber. And again, we've noted the complexity here of having all these multiple outcomes we're looking at. But even our exposure here is not Necessarily one exposure in terms of dietary fiber being one thing, there are many different subtypes of dietary fiber that all vary in terms of their properties and therefore functionality. Can you maybe just talk about this of the. That complexity of all these different subtypes of fiber, what that might mean for their intakes and then what you have noted from the evidence that maybe tries to parse between different fiber types themselves?
- [29:48]
B
Yeah, this is very eloquently said. And this is the main comment I get back from most people at the moment. Well, which fiber? Which is the fiber that does all the benefits? I'm going to take a tiny step back and just say that, yes, there are many types of fiber. The definition is a chemical one and it allows for lots of non starch polysaccharides to be included in that capsule. That's not hugely unique in the world of essential nutrients, though, because most vitamins have multiple forms, albeit none of them have as many forms as fiber. But it's not that. In the past, every essential nutrient has had just one singular form. And all of a sudden I'm introducing this idea of this range of fibers. So really happy with that. I thought that was going to be a stumbling block, but not too many people have pointed that out or thought that way, which is cool. So when people ask me what is the best type of fiber, I don't give them a clear answer because I don't have a clear answer. You can look at fiber in many different ways. One way to look at it is inherent in the food. So a fruit that has fibres in it, extracted and added to food, or synthetic, made in a lab and added to food. At the moment, we don't say there's a health difference between those three classes. We don't see a clear difference where inherent fibers are better for you for a chosen disease than an extracted or a synthetic. So that that really clears the way for food formulation in our food supply to have more fiber put into it. I don't think that's a bad thing at all. With inherent fiber. Obviously there's a nutrient bundling concept where if you have fruit, you're not just having fibre, you're also having the vitamins and minerals and that wouldn't necessarily be fortified in the food. So there's always a small vote for inherent fiber that's found in food above the extracted or synthetic. But when you only look at the benefits of that fiber, we don't see a difference between those three classes. A lot of people want a specific answer of which fiber I'M working in the area myself of, well, what are the fibers or things considered fiber at the moment that aren't doing function as opposed to which are the ones that are definitely doing function? You already said that fibers range in different classifications or types, so their viscosity, their solubility and their action in the body is different. That's fine, I think we should have a range of those. But I'm also really interested in looking at some of the smaller, smaller fiber structures to see if they actually meet and do physiological effect. So the definition of fiber typically says that they must have at least a DP, a degree of polymerization of 10 or more. However, most countries in the world also allow carbohydrates with a DP of 3 to 9 oligosaccharides into their definition of fiber. So you can add an oligosaccharide to a food, it'll bump up the fiber count that you can put on the label and you can promote it as a high fiber product. I'm really interested to know if those actually have an effect. Likewise for things like inulins, slightly more complicated with a DP of 10 or 12 on average. So just meeting that definition of dietary fiber more looking at carving out where are the functional fibres by excluding the ones that aren't functional. So less interested in actually nailing one fibre in the idea that it might do everything. More interested in cleaning up to have a cleaner definition of the functional ones. Because I think there's probably multiple ones, as you said, they differ in characteristics. We see a wide range of benefits with different health outcomes. So it could be that viscos ones are doing some things where non viscous ones are doing other things, but both actions are beneficial to the human. A bit of a workaround answer to your question?
- [33:12]
A
Sorry, no, no, absolutely not. I think that's a excellent, most technically correct answer that we can give. And I think this again, one of the interesting things I think suppose for this particular conversation is that while we may have evidence on specific type of those subtypes for certain outcomes, for example, people talk about those viscous fibers having a particular utility for LDL cholesterol lowering and that's why we have all this data around beta glucans and lowering ldl, but in this particular case where you are building for fiber to be classed as an essential nutrient and in and therefore having this kind of definition that we've talked about a bit earlier, or this kind of clarification around what a deficiency state would look like and therefore repletion we might have a case where maybe other fibres might speak to that a bit more directly. By that, I'm thinking, well, if we know there's certain fermentable fibers that maybe are more directly going to have roles within the gut microbiome, maybe those would fit into the definition a bit more. Knowing that we have these different fiber types that while they do probably multiple things, again another bit of complexity. There are some that are associated with more functions or some functions rather than others. And I don't know how that comes into our thinking about the essentiality question we discussed earlier.
- [34:31]
B
Yeah, the WHO recommendation is just based on fiber. They haven't drawn a line and said, these fibers, there's just this understanding and benefit that multiple sort of gains will be made in health should we increase fibre intake. So that was done. Despite the sort of caveat of all which fibers are most functional or which derive which functions, it's still there, that recommendation just to have more. It also should be probably recognized that if you're thinking about the inherent fibers in food, they tend not to be the same thing within a food. So food, a whole grain or a vegetable actually have a range of different fibres in it. So it sort of makes that complicated. That question of all, which is the pharmacological one that drives the benefit that we can extract a little bit moot point, because if you're having a food, you're having multiple types of fibrol at once.
- [35:15]
A
One of the things that, for a variety of reasons, some people who maybe don't want to accept the benefits of, let's say, dietary fiber, one of the claims I often see is something along the lines of, well, these benefits that we're pointing to towards to higher fiber intakes are actually just a function of the types of diets that tend to be rich in fiber. And maybe it's other things that are actually, let's say, causal in some of the outcomes that we're claiming. Can you maybe speak to, from the point of view of how we go through evidence, how we actually can determine the, let's say, the role that fiber itself, per se, is having in these outcomes that we care about, as opposed to some of these claims that it might be just serving as a proxy for healthy dietary patterns that we tend to recommend? And again, those things, it's hard to pull those two apart because one of the things about making them healthy is high fiber. But this is the type of claim that I've heard some people try to make.
- [36:17]
B
Yeah, for sure. Going a little bit further you can also think, is it actually a marker for healthy lifestyle? So if people are more focused on their fiber intakes, they might also be physically active, they might be more likely to go to their GP when they need to. So that conversation is had a lot because we want it to be linked to the evidence. Very simply, if you go back to the trials and you look at the ones where they've given them a powder, half the people had a powder that was fiber, half the people had a powder that had a placebo, we see an effect, we see an effect on blood pressure, on lipid levels or cholesterol, sorry, on body weight and on glycemia. So if it was only a marker for healthy diet, how is that powder delivered in a randomized controlled trial with a placebo, how is that doing a benefit if it was just a mark? Clearly we can attribute these benefits to fiber, but then recognize obviously that, yes, when you have a high fiber food, there's so many other nutrients in that. I don't think that's a detractor to say that we shouldn't recommend fiber. That just clearly more is. Well, yes, if you're recommending fiber and people get it from foods, they're getting additional benefits, not just the fiber. The benefits we know comes from fiber.
- [37:22]
A
I did want to come back to the microbiome because again, this is at the core of what we discussed earlier and that if we are seeing changes there as a result of a deficiency and then something that can be repleted, there's obviously something going on. And we do have quite a few lines of mechanistic work that discusses on that kind of plausibility of what's happening actually at the level of the microbiome and where dietary fiber comes in and how that relates to things like fermentation or short chain fatty acids. Can you maybe outline some of those from an overview level for people, what they need to know, what are we talking about with fermentable fibers and how that connects to some of these markers that we measure in terms of short chain of fatty acids or any other measure that might be relevant here for some of the microbiome changes that we could care about.
- [38:13]
B
So very simplistically, we eat the fiber, we put it into our mouths and we swallow it. The fiber is the carbohydrate that can't be absorbed by the human body itself. So it passes through the small intestine with very minimal sort of change, and it gets into the large intestine or the colon or the bowel, whichever way you want to call it, that's where most of the gut microbiome to live. And then they can actually digest the fiber. So they have the right enzymic sort of properties to break down fiber that we couldn't do. And when they break it down, they produce byproducts. The most recognized, talked about and studied are the short chain fatty acids, as you said, and the main three are acetate, butyrate and propionate. In the Nature Food article we do sort of spell out some of the very simplistic the benefits of each of those. What does acetate do in the body, what does butyrate do in the body? And what does propionate do in the body? As sort of the best studied evidence of what the gut microbiome is doing, we know that those short chain fatty acids pass into the human. But what we, what we also are beginning to understand more, and this is why it's one of the more exciting areas of science, is that there's so many other things that are also passing into the human. So there's a lot of excitement and claims about the gut microbiome's effect on, on really big disease states a gut brain axis. So the microbiome talking to your brain, communicating in things of things like Alzheimer's disease reduction, that is suggestive at the moment, that is not established pathways at all. But we do have ongoing research to understand more about what are those other things beyond the short chain fatty acids that the gut microbiome is providing to the human and how does the human response to them. So a lot of interest there. Again, we come back to your point of we can see transient changes, but are they important to health? Are they important to long term health? We don't know. So a lot of it is experimental. But all those experiments need to happen to build the evidence like we have for the more direct effects, the effects on cholesterol, blood sugars, colic, cancer, blood pressure and body weight.
- [40:10]
A
And I guess this is another area where as with many areas of research, there could be this double edged sword, right where you have this most interesting or really intriguing things coming out and various avenues to explore when it comes to the microbiome and particularly how diet influences that almost for many people. I'm sure it's a kind of pet peeve to say a new study comes out and it showed some type of change in the microbiome or this bacteria changed or whatever. And the presentation of in the conclusions and understandably maybe so is that this is a big deal and this is alluding to something that is incredibly important. And I think as you've noted, there's this kind of chain that we don't really have clear yet of doing X, seeing a certain change in the microbiome, being able to know that that's actually an important change and then finally that that change actually connects to a health outcome we care about. That kind of pathway is actually really difficult and needs a lot of work right now. I think that's probably one of the criticisms of some of the work that comes out on the microbiome. So from an over level, what is the kind of next number of years the types of work we would need to see to start building out the evidence base with a chain like that, to actually understand what outcomes or biomarkers we should look at, how we should define what is a successful change or not it does actually impact the health. There's all these different questions and I don't know, I'm not asking you to be the solution to everyone's problem of how to fix it, but what would things you would like to see that would help us trying to resolve some of those unknowns.
- [41:52]
B
And I go on a tangent from what you said though first and then come back to it. Really good point. I guess. I see those headlines in media that talk about the amazing connection between the gutter and nothing and I know the context of where it's coming from. I know it's experimental science. I know that it's not really an established disease pathway and I can distinguish between that and say, you know, fiber having a good effect on your blood glucose for when you have diabetes. So I know that inherently, but that must be super confusing if you don't already have that level of knowledge. You're seeing a hundred of those messages a day and you don't really know which ones are more superior, which ones are or which ones are linked to health. So that's. I, yeah, I always criticize nutrition, I guess as being so flashy. There's so many headlines and people have all these big claims. But still, even then I'm able to understand which ones are more serious and established versus which ones are just a headline for headline sakes. That must be incredibly confusing. Nutrition communication does have a very bad rap for that sort of stuff as well as not having objective markers of dietary intake in place. So there's definitely things that we need to work on as a field and how we deal with media. The work that I'd like to get done, I guess in the next 10 to 15 is largely by microbiologists and gastroenterologists. I would say that large groups like the Nurses Health Study run through Harvard, they do have microbiome samples. So if you think about a cohort that's been running for 35 plus years and having gut microbiome samples along the timeline, maybe not from the beginning, but certainly along the timeline, think of how much powerful research and understanding you can get from that. If they took a sample every two years, what is the change between an individual? Because if it's crazy, if the microbiome profile looks ridiculously different every two years for an individual, it really sort of says, well, we don't really know. A one time measure of microbiome doesn't relate to health and we don't know that yet. So they have the tools and the resources and the samples in place to sort of consider that if we saw a bit more stability across time in people's microbiome profile, if it didn't change that much and they have that sort of data set to then link it to health outcomes. So big studies that are already established, like the Nurses Health Study run through Harvard Health Professional Follow Up Study, are prospective observational studies. They do have samples, so they're probably where I would hope the research is going. Much bigger numbers, much more thorough sort of collection. They have the obvious inherent issues with any prospective observational study, but they also have existing samples. So if they were able to analyze them, which would cost a lot, and then link that to their existing data sets, you'd get a lot more information on the transience of the microbiome, but then also maybe linking it, if appropriate to health outcomes. So I guess I'm waiting for that as my main one. The more mechanistic work is being run by a lot of other people, people who understand a lot better the bench science behind detecting microbiome stuff and being able to comment on say, differences between what we shed, the gut microbiome that's in our poo versus the gut microbiome that actually exists and functions in our bodies. So we use a lot of the mediators of microbiome activity, the short chain fatty acids or other metabolites in the body, in the blood or in the breath, to comment on what the microbiome is doing. But I guess a greater understanding is really reading their density, diversity and function as they happen, as they're actually acting in the body would be another huge advancement.
- [45:11]
A
I think if we pull it to a more again general overview and this call that you make for thinking of dietary fiber as an essential nutrient. And let's say we can maybe work towards getting there. At the current moment, as we've already noted, virtually all guidelines recommend that the general population should be increasing fiber intake to some of these higher ranges that we see in comparison to population averages. If we did get to a point where fiber did get noted as an essential nutrient, as opposed to this current state now, where it doesn't have that status, what would be the benefit of that? What do you see as the potential utility of even trying to get this as defined as an essential nutrient?
- [45:56]
B
Yes, excellent question. And it goes back to one of the first things I said in this chat in. In that there's no one body that recognizes essentiality. I actually think it comes down to public and scientific acceptance. So one of the powerful things of putting this out is that people are now talking about it at the level and when we shared it with a lot of our colleagues around the world, the message we got back was, oh, I never even thought of that. But it does make sense. So public and scientific acceptance, I think, is sort of the way to get something confirmed as essential. Now, if it did start getting called essential and framed that way, there's a lot of political gain in that essential nutrients are sort of prioritized more at a government level and so the surveillance and monitoring of their intakes becomes a bit more important. So people get very concerned when they have low iron intakes, iron being essential, of course. We already know that we've had insufficient fiber intake for decades and there hasn't been a red flag raised at that level. So we think that the political prioritization will raise. If a government recognizes it as essential and they monitor it and it's low, they should then act to restore it because of the health gains. The cost of, say, changing the food environment, reformulating foods or reducing cost of foods that are high in fiber, such as fresh vegetables and fruits, would all be actions that cost something to a government, that then they could recapture that cost through the health gains should a population increase in fibre intake. So it's a political action, it's a way to prioritize fiber as well for health professionals and their communication to individuals and for individuals to maybe prioritize fiber as a carbohydrate metric or as a diet quality metric above others, because we do think it is that important. We do think the signal from dietary fibre and health is much stronger or more reliable or robust than other measures of diet or carbohydrate quality, I guess. So we think they're reprioritizing for governments, but also for individuals and for health professionals in the advice they provide their patients.
- [47:52]
A
It makes so much sense because I think weaves as you've I think alluded to when we're trying to change population intakes, we have these really useful avenues that could be explored in terms of fortification of certain food products that are very common. It's relatively easy to do depending on some of the things we're looking at. And so again if we have this essentiality there is a role for government that can be taken there. You'd probably also see more uptake by industry generally that they could use that within some marketing and want to do that. And even just around the understanding from a population level because only recently I saw something where I think it was based in the UK and on a survey most people were under the presumption that a higher fiber bread was more expensive than their typical white bread. And you look at all the chain of supermarkets and the prices were the exact same.
- [48:44]
B
Oh wow.
- [48:45]
A
Whether it was the whole grain or white across those main supermarkets for the in store brand. But again because it was thought of I suppose by people as this more of a, a luxury item or this kind of health food as opposed to it's just another type of bread potentially. And so there's maybe some acceptance that could go on there. One of the other areas, I suppose it would take away a common narrative I see in people who try to promote diets that are very low in dietary fiber or exclude plant foods which doesn't happen at recommendation levels across governments thankfully but is common that people will come across on the Internet. And one of those excuses or narratives is look, we have this nutrient fiber that is people are telling you you need this is non essential, you don't need this. And so therefore you can be perfectly healthy without it. And so I think it's maybe worth spelling out to people that actually we can answer that question with the data we have now. And for people that are consuming close to little to no fiber, we can be pretty confident in some of the things we say about that as a kind of a general thing to leave people with. What would your summary of the evidence be for those lowest intakes of fibers we typically see? How could we summarize the likely health effects of those?
- [50:04]
B
Yeah, well I didn't actually know there was group people saying have as little fiber as possible in the diet. There's some relevant to clinical management. Ibd, ibs, you should avoid fiber in flare ups but outside of flare ups you should be having as much fiber as possible. And that's been indicated in observational studies to be protective of future flare ups. So that advice can often get misconstrued. Avoid fiber full stop versus avoid during flare ups. But I actually didn't know that there was a general body of people going around talking about low fiber intake. So that's really interesting to me. I guess what I hear more is that low carbohydrate intakes is still a thing that people discuss, but fiber is a carbohydrate. So if you're reducing all overall carbohydrate, you might also be reducing your fiber, most likely, I guess, the overall takeover message for people who have incredibly low intakes. Let's look at some practical reasons of why people with celiac disease probably shouldn't have whole grains other than the ones that don't have things like buckwheat, the ones that don't have gluten in them. And so a lot of data on celiac suggests that they do have lower fiber intakes. But remember that fiber also comes from vegetables, legumes, fruit and nuts and seeds. So there's other avenues for people who have to avoid a certain food group that has fibre, such as celiac, where they can get their fibre through other means. That's an important message, I think, in it doesn't mean they are naturally going to have less fiber intakes than other individuals. For people who purposely choose to have low fiber intakes, I mean, I guess that's where we have the greatest benefit, the greatest evidence of benefit as well too. We really do see in our dose response curves for things like mortality, type 2 diabetes, heart disease, cardiovascular disease and colorectal cancer, we see the greatest benefits moving from the lowest intakes to moderate intakes consistently. There's always a big uptake from the low consumers to get the greatest health benefits. So I think if you're purposely going low fiber, which is still this new concept I'm trying to think about in my head as we talk, you're missing out on such an easy gain in risk reduction for your future self. So all those diseases, I wouldn't want to get any of those. I don't want colorectal cancer, I don't want type 2 diabetes. So purposely depriving myself of something that would protect me from them is still a bit of a strange concept for me.
- [52:13]
A
Sorry. And trust me, it is as insane as it sounds to you right now. But I promise you, there are people on the Internet that tell people to do that, to avoid even all vegetables for example. But it is as insane as it is sounding.
- [52:26]
B
Do they have a health reason for why that would be a good thing?
- [52:29]
A
Well, generally it's born out of more of an ideology and I don't think there's much evidence cited, but it is on the basis of people promoting all meat diet, for example. And they might start with some of the symptom resolution they get for X, Y and Z. But then from there it kind of builds a case of well, we don't actually need fiber. You don't need fruits and vegetables to get certain micronutrients, they can be gotten from animal produce, et cetera. And the case becomes quite intricate, but as it goes on gets more and more divorced from evidence and reality.
- [53:02]
B
Can I just say one more thing we haven't touched upon yet? It's about you just mentioned symptoms. The main issue of increasing fiber intakes is when you do that too quickly. So someone who's not used to a high fiber diet suddenly has half a can of beans which can have up to 14 grams of fiber. They could double their intake with a bean salad. They will experience, most people will experience some distress in terms of bloating and gas farting and stuff. That is really just because you've gone from a low intake to a much higher intake really quickly. And beans are the classic one. If you talk to beans about most people legumes, they're so high in fiber that people will say, oh no, I always get gas and bloat. It's really just that change in fiber intake. So if you make a decision for yourself to consciously increase fiber intakes, if you start to choose those whole grain products over refined grains and eat actively, eat more vegetables with their skin when appropriate, and have more legumes, nuts and seeds, just do so at a slower rate initially. Don't go all in, don't suddenly triple your fiber intent because you will experience some distress as that microbiome has to settle out and start to flourish and control itself with that sudden increase in food that it can consume. So that's my really only advice. That's the only symptom I know or negative about higher fiber intakes. It's if you do it too quickly.
- [54:14]
A
Yeah. And actually just from kind of practical experience of working with people on their nutrition, that is by far and away the number one reason why most people stop trying to go for higher fiber intakes is that initially they jumped too much. And there's also some sometimes weird individuality of they can increase their intake from chickpeas and lentils fine. But then they're adding like kidney beans and for them they need to do it very slowly and that gives more of a response. So just as you say, giving them that bit more time, that's an excellent recommendation. So before we wrap up, Andrew, is there anything that we haven't discussed or have forgot to get to that you would like to let people in on that came from that work or any other thoughts that have came to mind that we haven't got around to for other work?
- [55:01]
B
I've actually dropped, I think, three or four hints in this podcast about the current work that I'm doing yet to come out. So I'll probably touch base with you to let you know about those if they, if they prove something interesting and advance the field. The first question you asked me was talking about the current definition of essentiality versus a maybe a newer or modern definition of essentiality, which we didn't touch on. And I guess that comes down to, I mean, you are an expert in this understanding causal implication, causal language. It could be that essential nutrients are the ones causally associated with outcomes. That could be our new sort of framing of definition if we thought there was still value of having this tier of nutrients, essential nutrients. I think, yeah, moving away from just deficiency states and more looking at causal associations, causal language, causal implications would probably, probably be where that definition type would go in the future.
- [55:51]
A
Definitely would love to have a further conversation in the future all around those topics. I'm sure there's a lot of people that are listening right now that are very interested in the work that you've done today that we've discussed, as well as some of the work that's coming down the line? Where are some places they can keep up to date with you or your work or anywhere else you might want to send their attention towards online?
- [56:12]
B
For my work, I have a limited social media profile. I don't actually tweet or do things like that to release my own work. You could see me on research gate and LinkedIn, as sad as it is to say, and Google Scholar. Those are the three that I sort of maintain. They're great portals for me to engage with people and for people to request publications if they want to read them. Those are probably the three practical ones for me in this area.
- [56:33]
A
I will leave links to those in the description box for everyone listening, as well as all of the publications from Dr. Reynolds that we've referenced here as well as previously. And also remember, you can check out our previous conversation, episode 482. I would highly recommend you go back and listen to that. That brings us to the final question that I always end the podcast on, which will be your second time to get this, but no doubt it will have changed over time. And it's simply if you could advise people to do one thing each day that would have a positive impact on any area of their health, what might that one thing be?
- [57:06]
B
Was my last one Be kind to yourself. I feel like it was something along those lines. I moved away from diet and I really thought how do you give people a break? And it's, it's normally we're self critical of ourselves. I'm probably still in that sort of zone. We do put a lot of pressure on ourselves and we have expectations of where we should be or can be that really just muck up with our everyday happiness and satisfaction. I'm certainly on the bandwagon at the moment of appreciating small things in life and sort of trying to be satisfied and happy with small gains. So walked my dog yesterday afternoon and it was vaguely warm. We're having an awful summer here, but it was warm enough to walk the dog and it felt amazing. So yeah, focusing on small gains in your life and getting satisfied with just the little things that I think we just gloss over is probably my message today.
- [57:49]
A
Wonderful. Dr. Andrew Reynolds, thank you so much for taking the time to do this. For all that you've shared here in this conversation. I've really, really enjoyed it. As I've said to you before, your work more broadly has been really informative and helpful to me personally and I'm sure to a lot of people who have read it. So thank you for that and thanks for taking the time to do this.
- [58:07]
B
Thanks Danny. Great to talk.
- [58:21]
A
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