Transcription
Holy cow, this paper, this incredible paper just changed the way I think about fiber. This paper just changed the way I see fiber again. And it made me realize I might have accidentally misled you. Oops, my bad.
Anyway, let me back up. I hate it when people say just eat more fiber or fiber is good for your gut health because it grossly oversimplifies what is a complex, nuanced, and really interesting group of molecules. Saying [music] fiber is healthy is like saying Nemo and megalodon are both just fish. It's grossly misleading.
>> Don't touch the >> Some fibers can reduce inflammation, change your hormones in positive ways, slash your apple and cholesterol. Others can increase liver damage, increase inflammation and cholesterol, and quietly undermine your health. Not to mention your old factory environment, if you know what I mean.
In this video, I'm going to prove that to you beyond a shadow of a doubt. And I promise you, listen up. I promise you, if you watch until the end, you won't just walk away with deeper [music] insights and practical tools. You'll walk away with shock and awe that the whole world still sees fiber as something that it's not. I know that's [music] a big promise, but I can deliver on it. Just watch me.
At one dose, inulin could protect the liver. At another dose, it could actively poison the liver. The reaction was severe enough that researchers actually halted inulin fiber supplementation. This isn't a battle of good and evil. Same labels, radically different outcomes. Fiber isn't a single thing. You'll know more about fiber [music] than any dietician I've ever met. Chicken, fish, eggs, and meat might amplify the cholesterol-lowering effects of the fiber. That's counterintuitive, right?
>> Ooh, I'm fired up. Aren't you? Well, a quick note before we begin. For extra nuances, details, and all the references, and even a commentary from the senior author of this paper, the one we're about to review, don't forget to check out the associated Stay Curious Metabolism newsletter. I've linked it below. Thanks to you, it remains a top three bestseller in science on Substack across the globe. That's really amazing. Okay, thank you for that.
Now, data time. This video is broken up into five chapters to make it easier to digest and maybe ferment as well. Chapter one covers the design of this study and the unique characteristics of the diverse fiber types that they analyzed. Chapter 2 dives in on how one specific fiber can cause liver damage and inflammation and what that actually means. Then chapter 3 delivers a plot twist. What initially looked like a contradiction, and this is where I misled you, is actually a deeper level of nuance. And if you understand this, if you truly understand what we cover in chapter 3, you'll know more about fiber than any dietician I've ever met, and I've met hundreds. Then in chapter four, we're going to reveal a surprising finding about cholesterol that may change how you think about fiber. Then five, we're going to answer the big question, what can you actually do for your gut health? related to fiber today. So with that, let's get on to it.
Chapter one, that's two. One, the study. The study in question was published by one of my favorite research groups at Stanford, the Snider Lab, back in 2022. It was a rigorously designed human control trial involving 18 men and women who were given two different types of fiber. Arabinoxin, abbreviated AX, versus inulin. The study used this randomized crossover design, meaning each person received each fiber for 3 weeks separated by a wash out period to allow their microbiomes and metabolisms to reset. Good crossover trials always have a wash out period. In each phase, participants consumed increasing doses of fiber on week 1 10 g, week 2 g, week 3 g. Then after the wash out, each person had the other fiber. There was also a third mixed fiber arm. You see that here in blue. But as the results were largely intermediate, I'm not going to be spending too much time discussing this. You can see the actual paper if you want more details.
Now, I know what you might be thinking. 18 participants is kind of a small study size, isn't it? Well, here's the thing. This study was incredibly high resolution. If you think about your average study is like a sketch of Mickey Mouse. This is like avatar in 4K. They included thousands of data points, literally genetics, proteomics, metabolomics, lipidomics, serum, cytoines, clinical labs, you name it. They collected it. They collected blood, stool, dietary journals, even track poop mass and fart frequency. Yes, really. So, I'd take a deep granular study like this over a 10 million person observational cohort study with surface level data any day. This study was remarkable.
Now, before we dive into the results, let's briefly talk about the fibers themselves so you have a handle on what we're actually talking about. The arabinoxulin ax fiber it's built of a xyos backbone and arabinos branches and importantly it carries polyphenols like furillic acid which are bound to it and these might have anti-inflammatory effects through antioxidant action for example furillic acid is known for its ability to fight free radicals and boost the effects of other antioxidants like vitamin C and E. It's found in many foods including bran brown rice and bamboo. And because my ADHD is acting up a little bit and I had to find out, AI informed me that adult pandas consume 10 to 90 gram of furulic acid daily by virtue of being bamboo shredders. Anyway, ADHD spill over. In this way, this is key. AX is not just a simple fiber, but a Trojan horse for various polyphenolic compounds to get into the body. And we're going to comment on the biological relevance of these later in chapter 4. But first, for other fiber, inulin, which we've discussed before on this channel, comes from foods like chory, Jerusalem artichoke, onions, and leaks. It's a common fiber in many supplements. And what it is, inulin is a fructose polymer, a chain of fructose with a glucose cap, typically at least 25 or more fructose units. And unlike AX fiber, the other fiber, it lacks antioxidant polyphenols bound to it. So there's no Trojan horsing, so to speak. For what it's worth, this benapiber is really high in inulin. This Metamucil is high in rabinoxulin. Now you know. And AX and inulin, they're both classified as soluble fibers, but as you're going to see, their effects could not be more different.
That brings us to chapter 2 on inulin, liver damage, and inflammation. A subset of participants in the study reacted negatively to highdose inulin. They saw increases in liver damage markers, especially one called ALT. What ALT is is it's an enzyme that lives or should live in liver cells. It should stay in those cells. But if liver cells get stressed, inflamed, and damaged, they can leak out ALT into the bloodstream. That's what happens when your ALT is high on a blood test. So high ALT on a blood test, it's kind of like a smoke alarm for the liver. Or if you want another analogy and you're a Harry Potter fan like me, it's like Neville's Remembral of Liver damage. It flags that there's damage, but doesn't tell you what the damage is. And I'll give you a bonus point if you can tell me what Neville forgot in the sorcerer stone. And there is a correct answer. You can actually see it here.
[snorts] >> I can't remember what I've forgotten. >> Anyway, the reaction, the increase in ALT was severe enough that researchers actually halted inulin fiber supplementation for those individuals out of concern for potential medical complications. This isn't a trivial signal. In fact, the authors also cited pre-clinical evidence that long-term highdose inulin supplementation in mice has led to liver damage and even liver cancer. So, these are real biological signals. They're meaningful. This isn't just noise.
And this is what's curious. This is the plot twist. As it turns out, inulin might actually help support liver health in some people, but at moderate doses. But inulin can become harmful in sensitive individuals at high doses, which brings us to chapter three.
Next level fiber nuance. This is also what I was referencing when earlier I said I might have misled you or I guess I did mislead you in a way. For those who remember a prior popular fiber video, which you can still go watch, the data still stand on inulin. I made the case in that video that inulin can be beneficial. It can improve liver health, protect against fructose, sugar induced liver stress. How a specific fiber through a precise mechanism can immunize the body against sugar and what that sugar becomes will blow your mind. Those data still stand, but at low moderate doses. What inulin does is it adapts the microbiome, bestows the ability to convert fructose, a sugar into protein and antioxidants that can protect the liver, reduce liver fat, improved fatty liver substantially and enhance metabolic health.
So what is the story here at the high level? It's not that inulin is bad or good, but rather the dose in the host, that interaction matters immensely. And I want you to pause and consider how remarkable that is. At one dose, inulin could protect the liver. At another dose, it could actively poison the liver, causing liver damage in a human randomized control trial with potential severe consequences over the long term. That's scary, but it's also fascinating. This isn't a battle of good and evil, but of complex characters.
And quickly, what about inflammation markers more broadly? Interestingly, highdose inulin triggered a separate dose dependent rise in inflammatory markers like IL6, which in the author's own words suggest a systemic whole body inflammatory response. So in short here, there are multiple mechanisms by which high dose inulin fiber can harm although low to moderate dose can heal. And if you want this simple takeaway, I know I've thrown a lot at you. If you tolerate lowd dose inulin, say 10 grams per day, it could offer really tremendous metabolic health benefits. See the other video for more, but at higher doses in the wrong patients, long-term inulin fiber can backfire, harming your liver. Kind of cool. If you want to go back and listen to chapter 3 to let that sink in, it is really deep. But let's get on to chapter 4, which is actually my favorite.
Ax fiber and LDL cholesterol. For those of you who know me, you know I'm a lipidender. So maybe it's not surprising that the cholesterol response was of greatest fascination to me. The AX fiber caused a dose dependent reduction in LDL cholesterol with drops over 20 milligs per deciliter at the highest dose. You see that here in red. But by contrast, obviously inulin fiber had no effect on cholesterol. In fact, some people even saw increases in cholesterol with inulin supplementation. And while individual responses varied as they always do, the group level differences are striking. This finding highlights just how incomplete and misleading general fiber is good for cholesterol claims really are. These are both soluble fibers, but they have drastically different effects on cholesterol across groups, but also within individuals. At a population, AX is far more powerful at reducing cholesterol, and inulin isn't.
But that alone isn't all that interesting to me. I don't really care about LDL going up or down. I care about asking how. Because this is not a simple fiber blocks cholesterol absorption story. There are at least three additional biologically plausible ways by which AX fiber can lower cholesterol. I'm going to go over these three. Try to hang on.
First, bile acid binding and excretion. So, pooping out. AX can bind bile acids which are synthesized from cholesterol. And when these AX bile acid complexes are excreted, the liver needs to manufacture new bile acids. So it draws from circulating cholesterol to do so, which can lower your LDL cholesterol.
And two, shifting bile acids also is a signaling mechanism. AX appears to alter the composition of the microbiome and bile acid pools not only within the gut, but also systemically in the bloodstream. Bile acids circulate throughout the blood and bind to receptors in the liver like LXR or TGR5 pathways. They can directly reprogram your metabolism including cholesterol and lipid metabolism.
So if mechanism one is like a siphon, mechanism 2 is signaling and mechanism 3 builds on that signaling. The polyphenol delivered. Remember how I said Trojan horse earlier? Let's talk about that. AX fiber can act like a Trojan horse. It fies polyphenols into the gut and once these are released by microbial enzymes or R enzymes, these polyphenols can function as signaling molecules circulating throughout the body and modulating lipid metabolism and whole body metabolism. So you see that all here in this beautiful complex interesting picture and taken together what I'm really saying is AX fiber may lower cholesterol through a combination of extratory loss so in your poop endocrine like signaling like a hormone and microbiome mediated bioactive compound delivery these polyphenols this isn't just reducing cholesterol absorption.
And adding another fun layer to this AX fiber cholesterol story when the researchers looked at what predicted strong cholesterol response. They found something that really surprised me. Participants who responded to the AX fiber with the largest decreases in LDL cholesterol also tended to have high protein intake in absolute terms and in terms of ratio of protein to fiber. The author is actually right. Participants with higher dietary protein consumption are likely to have a better cholesterol response to AX fiber. Now, the next question we should ask the other is, is this a true causal relationship or just a spurious one? That's not yet clear. But if it is a causal relationship, it raises a fascinating and pretty ironic possibility that a high protein diet, think chicken, >> a big boy, >> fish, eggs, and meat combined with AX fiber might amplify the cholesterol-lowering effects of the fiber. That's counterintuitive, right? We usually think of high protein diets, especially animal-based high protein diets, as potentially increasing cholesterol, not reducing it. But if protein intake modifies the microbiome in a way to enhance AX fibers ability to say bind bile acids or alter signaling, it could have a synergistic effect on lowering cholesterol. So in a way, eggs and chicken and meat could help lower cholesterol. I'm not fully sold on the causality yet. It could have easily been a non-cositive correlation, but it's definitely worth exploring further because like any good research, this study answers some questions, but opens up many more.
Now, that brings us to chapter five. What can you do for your gut health today based on these data? I know you're asking that question, what can I do for my gut health? What does this actually tell me? Well, unfortunately, I don't have a perfect answer. If you want to go through the paper for yourself and wrestle with the dozens of italicized Latin names and bacteria and then figure out what probiotics to take, you can be my guest. It's kind of a shotgun approach, but at a high level, I don't think that's the functional way to go about treating your microbiome because the microbiome, it's a complex ecosystem where different microbes play different roles in different people. That means, in my opinion, the goal shouldn't be to target or chase specific bacteria, but rather focus on improving overall functionality of your gut, the ecosystem as composite that ecosystems performance. That said, I'll also be the first to admit this advice has its limitations, too, because clinical tools that assess microbiome function think the specific composition of your bioassm pool are still largely unavailable. So, for example, in this study, they found that this AX fiber that we were talking about, it could increase levels of UDCA or LCA, which are both secondary bile acids that might carry benefits both on lipid metabolism and even longevity. I have two separate videos on each of these.
All this amounts to me trying to put into words what a simple human gesture, a shrug, might express succinctly. We just don't know. But if you're wondering what I do for what that's worth to you, here's my personal protocol, and I'll keep it simple. One thing I always do is intermittent fast. I eat in a timerestricted feeding window, always less than 10 hours and often less than eight. This gives my microbiome and gut lining time to reset and recover. And I also try to eat meals at the same time every day. This supports consistent circadian rhythmicity, helping to regulate not just digestion, a broader metabolic and immune processes. Think of it as harmonizing your biology, your microbiome, and your human biology. Also too, I try to eat fermented foods. I have a pretty sensitive GI system by virtue of my ulcer of colitis history, but I do tolerate some fermented foods pretty well at moderate doses. These include sauerkraut, goat milk kafir, blue cheeses, pickles, and fermented olives.
Finally, the last addition to my gut health protocol, the newest Winnow Labs probiotic. I also take a probiotic from a company called Winnow Winnow Labs. And as a full disclosure, I'm now on their scientific advisory board. So, yes, I do have that conflict of interest. But I was drawn to this particular formulation because it's designed not just for general gut support, but for a specific functional role, binding and neutralizing microplastics, which as you may know are increasingly pervasive in the environment. This is meant to serve as a sort of biological shield from the inside out, giving your microbiome a capacity it previously didn't have. And if you want to learn more about microplastics and particularly the role on heart health, I've written a dedicated letter to that topic here. This is my way of proving to you this isn't just a fluff plug for a supplement. It's something that I'm genuinely interested in and take and I can back up why. But if you don't want to read the full letter, the TLDDR too long didn't read is as follows. The researchers behind Winnow Labs probiotics, they screened literally thousands of bacterial strains to identify those gut bugs that preferentially bind to plastic particles. You can see that here. The naked bug doesn't bind plastic and the winnow bug binds a ton of plastic, allowing these plastics to be trapped in the gut and excreted, pooped out rather than being absorbed into the body. If you're interested in trying this probiotic, the one that I take, you can use the code stay curious for 15% off.
So, that's what I've got for you today. As always, if you discovered something that works well for your gut, whether it's a practice food or a supplement, I want to hear it. Please share with the community. That's a great contribution.
Now, finally, here's the real punchline. Fiber isn't a single thing. It's not a single intervention. It's a broad category of biologically active compounds. And treating fiber like one thing, it's a gross mistake. In this trial, two soluble fibers, both marked as gut healthy and often lumped together, produced radically different effects. At high doses, one provoked liver stress, liver damage, systemic inflammation in a subset of people, and the other lowered LDL cholesterol and apple in a clinically meaningful way likely through multiple mechanisms that interact with diet, the microbiome in the host. Same labels, different biology, radically different outcomes.
that this is what excites me is the future of nutrition. Context matters, dose matters, and the person, the host, me, you, what makes us individual matters most of all. And it's my sincerest hope that the era of blanket advice like eat more fiber is fading like a fart into the wind. And what's replacing it is precision. Matching the right compound to the right physiology under the right conditions. So next time someone says just eat more fiber, don't nod along. Ask the questions that matter. Which fiber, at what dose, and in whom?
Forgive me for going on a bit, but I think that's what sets our community apart. I really try not to dumb it down because I respect your intellect, and I believe you want the nuance. I think it's my job to communicate those nuances in understandable ways. So, tell me, grade me. How did I do? And if the answer per chance is A+, great job. Do me a favor and join our stay curious community at the newsletter as well. That's an amazing way to support us and where you're going to get all the greatest details, nuances, up-to-date science, and commentary from authors of the paper. And finally, this time for real, before you add more fiber, ask yourself, are you making an informed choice or building protocols on platitudes? Stay curious. And thanks, [music]