Fiber: Independent Benefits or Just a Proxy for Healthy Foods?

0:00Before we get into today's episode, this is just a quick note to let you know that what you're about to hear is a segment that we've taken from one of our larger question and answer style premium exclusive episodes that we do now and again for our premium members. So you are going to hear a segment of that covering the topic of today, which covers the very interesting topic of whether the health impacts we see associated with fiber come from its independent effects, or is it simply acting as a proxy for other healthy food groups? And how do we disentangle that from research. But like I mentioned, this is from a larger Q &A episode for our premium subscribers, in which we got into many other really interesting topics, including for a match dose of red meat, does the exposure frequency matter?

0:46For MTHFR gene mutations, which type of supplementation might be useful? How do we compare typical over-the-counter fish oil supplements versus the pharmaceutical-grade products we see in the main studies? And then what are the health impacts of plant-based saturated fats like coconut products? Do we need to consume whole grains within the context of an otherwise healthy diet? And then could AI pose a threat to doing rigorous nutrition science? All of these were covered in our full-length Q &A episode. If you're interested in listening to that episode in its entirety with all of those seven questions covered, then please check out information in the description box about how to become a premium subscriber that will also support our work.

1:31It'll give you access to the full back catalog of all our premium exclusive episodes that we publish every month. And of now, there are currently more than 50 of those that you can go and listen to. And you also get study notes to all our regular podcast episodes as well. So check that out if that could be interesting to you. But in the meantime, please enjoy this particular segment from our most recent Q &A episode. I hope you find it interesting.

2:11Hello and welcome to another episode of Sigma Nutrition Radio. My name is Danny Lennon and with me is Dr. Alan Flanagan. Alan, how are things? I'm very well, thanks. I'm having a nice, slow summer, so everything's good. good well deserved after probably many months of chaos and work that we'll probably hopefully see soon once some of your publications see the light of day that are in the works but yeah at the moment it's a bit of a waiting game for some of them they're at various different stages exactly i always find that the first 98 of the process of like writing up and vetting it on your own end before you submit is okay.

2:49And the last 2 % is so painful that it makes you question whether the previous 98 % is, or any of it is in fact worth it. Yeah. There's really something about that last yard of getting it over the line that is never really enjoyable. I can't see how anyone enjoys it. But the good thing is, I guess, from your experience, you'll probably end up forgetting about all that pain pretty quickly and then think, oh, great, let's do that process all over again. Let's just repeat this. Yeah, there's a real case of Stockholm syndrome, I think, in research. You just can't get away from. No, you're very much committed to helping the endeavor that is science.

3:28Exactly. I salute you for that. Today, we've collected a whole range of questions from listeners that we're going to work our way through. We've picked out what we think are going to be the most interesting that tie into some concepts that we've discussed on some previous episodes, as well as kind of build off some of them as well. and we'll work through these and hopefully give some answers that might be of a utility and we'll also add some notes related to these afterwards if you want to go back and check over anything that we end up do discussing but to get going we may as well just jump in and start working our way through the first question that we're going to tackle here alan relates to potential independent effects of fiber.

4:13And of course, we've discussed fiber on a range of different episodes, as well as looking at overall healthy dietary patterns that tend to be high in fiber. And so this question touches on something that I think we see claims in a variety of places that speak to this. So Sam asks, it seems to me that a perfectly reasonable way to interpret the strong relationship between fiber intake and its various beneficial health outcomes is that fiber is fundamentally a composite of or surrogate for total fruit, vegetable, legumes, and whole grains. I'm not sure why we would necessarily assume that fiber itself in isolation from those foods would have nearly the same effects.

4:56Before maybe get you to chime in this, Alan, I think there's probably two distinct things going on here. One, the kind of final thing that I presume we'd be very much in agreement with is that fiber in isolation isn't going to have the exact same effect as an exposure of all these different food groups that were mentioned because they contain other things than fiber but i think what the question is really getting at is and this is something that some people tend to hypothesize as well and say maybe the benefits per se of fiber are overblown or they're just simply a proxy for these other things that are causing that benefit and the fiber itself maybe isn't the thing that is as important for that health outcome and so So we probably need to focus in on that of while there are other things those foods are useful for, of course, it can be difficult to disentangle fiber intake from some of these things like whole grains or total fruit and veg, et cetera, that there are probably some specific cases where we could look at fiber as the exposure itself that per se is having some type of an effect.

6:00So given that, maybe let's start working through this for you. what way would you start parsing through this kind of complex interaction of these different exposures and how we should actually think about potential independent effects of fiber per se yeah it is a tricky one because the difficulty in disentangling as the question posits the independent isolated effects of fiber from other beneficial compounds that we know would be plentiful in a diet of legumes, whole grains, fruits and vegetables. In epidemiology, of course, we have independent effects, independent associations, sorry, for each of those, which kind of further complicates things, right?

6:50So you can see analyses that don't necessarily include adjustment for dietary fiber, where you would have an association with lower risk of cardiovascular disease with high fruit and vegetable intake. You can see associations, quite strong associations and consistent associations with lower risk of really pretty much any outcome cardiovascular disease, cancer or metabolic disease with dietary fiber intake from whole grains. And you can see independent associations for whole grains adjusted for fiber intake. So I think that this is a tricky one. I think that we can also then be helped by looking at analyses that have considered specific forms of fiber from foods.

7:43There was a nice paper in 2013 or 14 from Threepleton and colleagues, which was in the BMJ, which actually looked at food sources of fiber. So they looked at total dietary fiber, and this was specifically looking at the association with cardiovascular disease. They looked at fiber subtypes and then fiber from food sources. And so as we might predict, total fiber intake was associated with a 10 % lower risk of overall cardiovascular disease and coronary heart disease. Insoluble fiber and fiber from cereal grains and vegetables also inversely associated and fruit fiber. But in that particular analysis, there wasn't an association for legume fiber.

8:29So we could say that potentially the source of fiber matters. Of course, there are then also independent associations with legumes and lower risk of cardiovascular disease. So I think isolating independent effects of fiber in epidemiology from the constituent components of foods, even with statistical adjustment, which doesn't wipe away the, it's obviously a statistical model. It's not necessarily saying that the remaining aspects or characteristics in fruits, for example, are suddenly irrelevant and don't exist. So it's never a full, true isolation in the sense that we would achieve in controlled trials.

9:09It's difficult to disentangle. We have independent associations for specific foods and food groups in this context that are sources of fiber in the diet. And we also have very consistent associations with total dietary fiber intake. You can then, I think, be helped by looking at evidence that we do have from controlled feeding studies. And there are obviously a fairly large body of evidence that we can have to look at that has looked specifically at effects of certain intakes of dietary fiber compared to lower fiber intake with the same composition of foods or distinguishing specifically between, for example, whole grains versus refined grains.

9:51And that can add to the picture a little bit by suggesting that there are probably characteristics of a whole grain that may be associated with some of the beneficial effects we see with whole grain intake in epidemiology, but that's specific to the grain, the structure of the grain, or sorry, the integrity of the grain structure, not necessarily the isolated fiber intake. So if I was to parse this evidence overall, my perspective has always been, I don't think it is necessarily just fiber intake in isolation that explains effects of whole grains. In particular, I think that's demonstrable from other beneficial aspects of the total grain compound.

10:35I also then think that within the grain conversation in this, I'm also not particularly convinced. We have this dichotomy that we typically think of in terms of whole grains versus refined grains, but even the epidemiology of refined grains per se is not particularly suggestive of an overall just detrimental effect it very much depends some of glengosser's research has been very interesting in this respect the source of the of what we consider a refined grain matters and where they might be what are termed staple grains like populations consuming white rice for example you don't necessarily always see adverse associations compared to what we would also often consider refined grains which are more in the kind of realm of junk grains for want of a better term.

11:25So is there an independent effect of fiber? I would say that there probably is, given when we parse both epidemiology with populations and often assisted in this context with populations consuming much higher levels of dietary fiber and specific sources of fiber. And some of the comparative studies with populations eating relatively subsistent diets in Africa compared to Western populations have been quite instructive in this regard. 65 grams of fiber a day and almost half of which is like resistant starch and otherwise. And we have a body of controlled feeding studies that would allow us to say that there probably are specific effects to those fiber types that would explain the associations we see with fiber and epidemiology.

12:13Do I think it's the only explanation for the effects or the associations that we would see for whole grains or for fruit and vegetable intake or for legumes? Absolutely not. I think there are multiple components of those, particularly for fruits and vegetables as well, where you have other components in terms of micronutrient and phytochemical or what we put polyphenols as an overall class within that. And that would obviously be particular to fruits and vegetables for whole grains, obviously other characteristics of the grain kernel and the structural integrity of that grain. And for legumes, a similar kind of concept arises in terms of like resistant starch and other characteristics that could fall within the umbrella of fiber, but are having other effects, other beneficial cardiometabolic effects.

13:04So I think it's likely an interaction. And I don't think at least with epidemiological methods, we'll ever fully be able to disentangle associations. We will still see associations with fiber, but obviously the specific kind of independent effects of foods will never be specifically isolated in that context. Essentially, we can certainly have confidence that the type of high fiber dietary patterns that we see associated with positive health outcomes or lower risk of various chronic diseases are indeed imparting that lower risk, but that is not all necessarily down to the fiber content per se. That type of dietary pattern, as you've outlined, has multiple other things that we know are likely influencing that.

13:46At the same time, it doesn't mean that the fiber is just simply happening at the same time and doing nothing. And we have good evidence that we can triangulate to say that there are things or that the fiber part per se is contributing part of that health benefit we're seeing with those associations. And I suppose then even we could get into specific fiber types, as you mentioned, if we look at a subtype of fiber and a specific outcome, we can see mechanistically why that would be having a certain effect. I don't know, the one we talked about with some of the LDL lowering episodes are around like use of viscous fibers, and it's particularly that type of fiber or beta-glucan that's having a certain effect on blood lipids, as opposed to it simply just being in fruits and vegetables or grains.

14:30But like you say, it's very difficult to disentangle how much of these effects from a dietary pattern perspective are down to each of these components and again not to bring us in an area that we could probably another rabbit hole we could go down but you mentioned earlier around the adjustment for that and there's many situations where adjustment wouldn't be what you'd want to do because the potential benefit there is through that potential pathway and so you can't just adjust out for some of these factors or adjust for fiber when some of these food groups are having their effect, some of which is due to the fiber itself.

15:06And so it complicates the picture of how to disentangle some of the epidemiology. Yeah, I think so. The potential for over-adjustment when fiber is a kind of component of your exposure, if it's whole grains or vegetables. Yeah. I think what would we have better evidence for in a kind of controlled trial, controlled feeding study context that would allow us to say that the fiber is, because you brought up that point, I think it's really useful. So one, I think cardiovascular disease, I think we can say that those associations, when we see for soluble fiber and we see certain food sources of fiber, I think we can probably say that there is potentially an isolated, independent effect of fiber because we know from controlled feeding studies what effect soluble fiber in particular has on cholesterol recycling, on bile acid metabolism, on all of these mechanisms that lead to a reduction in circulating levels of cholesterol.

16:04So I think that we could probably say with slightly more confidence could be an independent effect of fiber or would be. And I think in relation to colorectal cancer, I think we have pretty good evidence from some of which, but I guess we focused more recently on red meat specifically, but again, from a kind of body of well-controlled studies relative to some of the comparative studies that we've seen, cross-population comparative studies that have been quite interesting. The mechanisms that we know influence colorectal cancer risk and progression, and the risk factors for that are almost uniformly turned in the other direction by dietary fibers, specifically on the fermentation of those fibers in particular and the production of short-chain fatty acids and protective effects on the epithelial bilayer and all of that.

16:55So they're the two that I think I would be more confident describing or attributing the reduction in risk that we see in epidemiology to a particular effect of dietary fiber. And, but yeah, I think for a lot of the other associations, we see it will always be difficult to disentangle specific isolated independent effects of fiber from other component parts of what are food groups that we typically are quite convinced that they are the kind of the sum of their nutritional and phytochemical parts in many respects. perfect so that does us i think for that question hopefully that was of utility to sam we'll move on to the next one that talks a bit about exposure and particularly exposure frequency as opposed to the actual total dose that was sparked off by something we discussed on our recent red meat episode so roy asks regarding testing exposures like your recent episode regarding red meat where most times exposures were measured in grams per day, what do we know about the differences between eating red meat every day and the same exposure in one to two meals, that's coming from steak or burgers, for example, every week, but with no red meat on most days.

18:10So simply here, we're looking at those exposures that we maybe mentioned where we would likely see risk. Is there any way or any evidence that helps us determine does how that's distributed across time actually make a difference or is it simply that total absolute exposure over, let's say, a period like a week? Is there any evidence that you've come across that might give us an answer that could be useful here or how should we understand some of these exposure or those numbers we get from some of these epidemiology? So I typically think of it in terms of the total exposure. And I think most of the research points us in that direction.

18:50And I think that's quite an important part to parsing some of the findings. I mean, there's a study that immediately comes to mind with this question, which I know we've probably discussed before and still gets passed around on social media a lot, which is the Alberta Tomorrow Men's study, which was a very nice analysis published, I think 2019 or 20, which basically looked at different levels of red meat and then calculated risk estimates for those different levels of red meat at different levels of corresponding fruit and vegetable intake. The study, I think it's misinterpreted a lot, but what I found interesting about that study, which I think speaks to this question, is the highest category in that particular our study was consuming.

19:44Thanks for listening into today's episode, which was a segment taken from one of our Q &A episodes. If you want to listen to that episode in its entirety, where we not only covered this question, but six others, then you can check all of that out in the description box where you're currently listening, and you will be able to get the full episode in its entirety as a Sigma Nutrition premium subscriber. Not only do you get those premium exclusive episodes every month, but you also get detailed study notes to all our regular podcast episodes as well, in addition to it being the primary way that you can support our work and what keeps the podcast functioning.

20:23So thank you for considering being a premium subscriber if you do so, and hopefully it allows you to get much more out of your learning from these podcasts by going a bit deeper, understanding that content a bit more, retaining more of that, and being able to revise it quite efficiently. So all of the information about that is linked in the description box. Please give it a consideration and give it a go if you think it might be something useful for you. And for those of you who do, I'll see you inside on the membership. And for everyone else, I hope to see you back for the next episode of the podcast.

20:56Until then, have a great week, stay safe, and take care.