Fiber That Fights Back

Your gut can love fiber, or fight it. 

We unpack why the same bowl of beans leaves one person energized and another doubled over, and how timing, dose, and microbiome diversity decide which way it goes. Drawing on clinical experience and a landmark Stanford study from Erica and Justin Sonnenburg, we break down the difference between piling on fiber versus preparing your gut to handle it, and why fermented foods often deliver a reliable boost in diversity and lower inflammation.

We start by defining a healthy gut: a strong intestinal barrier, low visceral hypersensitivity, and a diverse community of microbes that churn out short-chain fatty acids. Then we connect the dots between food and lifestyle, how sleep, stress, movement, and social health shape the gut-brain axis and change how you feel after a high-fiber meal. Think of fiber like training, not a test. 

Just as jumping into a max-effort workout can spike inflammation, adding a lot of fiber to a low-diversity microbiome can cause bloating, cramps, or bathroom swings. The fix isn’t less plants; it’s smarter progression.

You’ll hear the practical plan we use: start low, go slow, and mix fiber types while you build tolerance. Use cooking strategies that ease fermentation, soak and rinse legumes, pressure-cook beans, cook and cool starches to boost resistant starch. Layer in fermented foods like yogurt, kefir, kimchi, sauerkraut, and tempeh to raise microbial diversity, then steadily increase fiber by a few grams every few days. Over weeks, your microbiome adapts, the gut barrier strengthens, and fiber shifts from irritant to ally, supporting heart health, blood sugar control, satiety, and lower cancer risk.

If you’ve ever said “I can’t do beans” or “broccoli wrecks me,” this guide shows how to turn those foods into fuel. 

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Chapters

• 0:00 Section A

Transcript

SPEAKER_00: 0:10

Yo plant-based buddies, welcome back to season three of the podcast. This year's gonna be amazing. We'll be talking about all of the different pillars of lifestyle medicine, from nutrition to exercise to stress to sleep and everything in between. Yo, plant-based buddies, welcome back to another episode of the podcast. Today we're gonna be talking about fiber and why sometimes it fights back. I always say when it comes to fiber, start low, go slow, keep increasing over time. It can take weeks for your gut to adjust to new diversity of fiber as well as to an increase in quantity of fiber. Now, the average intake of fiber is about 14 grams, and that means that 95% of Canadians aren't getting enough fiber. It seems we're so worried about protein or cutting out carbs or going low fat. People forget that fiber is one of the nutrients the most associated with chronic disease risk reduction. Basically, if you increase the amount of fiber in your diet as well as the diversity of fiber in your diet, the risk of almost all chronic diseases drastically goes down. Now, fiber only exists in plants, and every type of plant has a different type of fiber. And that's why when it comes to gut health, it's not just the amount of fiber you consume, but it's also the types. It's very important to know that fiber is simply an umbrella term. And when it comes to fiber, we can talk about viscous fiber versus fermentable fiber versus soluble or insoluble fiber. Fiber is simply a compound or a class of compounds, and there are different, different, many different types of fibers that all behave differently. So today's episode is meant to review fiber. I've already done an episode on fiber in the past, you can go check that out. But today's episode is also about how fiber can fight back. And while some people will just see improvements in their health parameters when they increase fiber quantity and variety, some people will actually see it backfire. They'll notice that once they start eating more fiber, they get bloated, they get stomach cramps, they get pain, some people get diarrhea, some people get constipation, and other people just feel generally unwell. And that's what we're going to talk about today. A study done by gut health experts at Stanford that was done a few years back, but is still very relevant today to understand why, for some people, they have a hard time increasing fiber. So fiber gets praised everywhere. It's good for your gut, it's good for your heart, it's good for your blood sugar, it's good for longevity, but there is still a nuance that rarely gets discussed. And that's in certain situations, fiber can actually behave in a pro-inflammatory way. Not because fiber is harmful, but because timing, dose, and your gut readiness does matter. If your gut is not able to process an increased amount of fiber in terms of quantity or variety, it might suffer. So today we'll break down all of this nuance in a simple practical way. And the goal is not to scare anyone or to be extreme, is just to explain basic gut physiology so that you can improve your health in the meantime. So, before talking about how going too soon, too fast with increasing fiber, how that could harm your gut or even create inflammation, it's important to define what a healthy gut actually looks like. So, gut health is not only about digestion, it also includes several key features. Now, an intact gut barrier is a gut barrier that selectively allows nutrients through. It has low visceral hypersensitivity, and also it's made of a healthy gut flora that produces short-chain fatty acids, amongst other beneficial postbiotic compounds. Now, that was a mouthful, but what I mean is that a healthy gut is a gut that doesn't have any gut inflammation in the lining. Now, the gut lining is made out of one layer of cells called colonocytes, and these kind of regulate what is able to go in to get absorbed from the gut lining through to your bloodstream and what gets filtered out. And a healthy gut has low visceral hypersensitivity. What that means is that it's one of the concepts of IBS or irritable bowel syndrome, where the when the gut gets overly distended or stretched, it sends pain signals to our brain. And that's why people with well with IBS will absolutely see their symptoms change in situations of either increasing certain types of fibers too quickly or eating new foods in too much of a high dose, or even see their symptoms fluctuate according to their mood. There's a direct bidirectional communication pathway between the brain and the gut. We call it the gut brain axis. And gut health works both ways. It can impact mental health much in the same way as mental health can impact gut health. So low visceral hypersensitivity simply means a gut that's adaptable to different stimuli and to stretching without causing excessive pain. Now, a healthy gut is also made out of healthy bacteria. And a healthy community of gut microbes that produce beneficial compounds that we call postbiotics, with the most important types being shortchain fatty acids, is pivotal to having a healthy gut with minimal inflammation. Now, one of the strongest predictors of gut health is living an anti-inflammatory lifestyle. Basically, having a healthy diet, getting enough movement and physical activity in, having a proper sleep hygiene routine, managing stress, avoiding toxins that are known to disrupt the gut, and to be socially connected with friends and to live a life of passion and purpose. So it's not just about what you eat, but also about how you live. But if we talk specifically about food and specifically about food nutrients, fiber quantity matters and fiber diversity matters. I mentioned that most people are getting about an average of 14 grams per day or less. That's 95% of the population not getting enough fiber. We should be consuming about 14 grams for every thousand calories we eat. So for women, that would be about 25 or more grams, and for men, let's say about 30 to 35 or more. That we probably evolved on diets that contained over 50 to 75 grams of fiber per day. So just even meeting the minimal requirements is quite a hassle for a lot of people. Now, before I dive deeper in the gut health study I was referencing earlier, I want to compare exercising and fiber intake. Weird analogy, but think about someone who's never trained before, who's never gone to the gym before. So they walk into the gym and they're gonna do an intense workout, they're gonna lift heavy weights, they're gonna do high volume, and what do you think is gonna happen next? Well, they're gonna get muscle damage, they're gonna get muscle inflammation, and these inflammatory markers will actually leak into the bloodstream, and we'll see blood markers like CPK or creatin phospokinas start to rise, and in extreme cases, we can actually see myoglobin enter the bloodstream, and that's a protein that stresses the kidneys. Now, hospitals see this after intense exercise about people who like, for example, join CrossFit for the first week and go all out, try to follow the experienced lifters that have been doing this for years, or people that join spin bike communities and go all out. I mean, I've seen two cases this year of people going all out during a workout while being untrained and not progressing slowly to higher intensities, going all out the first session, and they get muscle inflammation, muscle damage. Now, if we would do a blood testing, these people will actually see inflammation going up. Now, that doesn't mean that exercise is bad for you. It simply means that you went too hard too soon, and dose and progression will decide whether it helps or harms you in the short term. And fiber actually works the exact same way. Now, fiber is generally anti-inflammatory, and most studies, pretty much all studies, show the more fiber you consume, the better gut health you have, the more diversity you have, the better gut health you have. And the the you basically see a reduction in the risk of all chronic diseases. I mean, your cholesterol will go down, your blood pressure will go down, blood glucose control will improve, cardiovascular risk will go down, cancer risk will go down, with colon cancer being probably the one that is most impacted by increased fiber intake. But when you introduce fiber too quickly into an untrained gut, fiber actually behaves like a nirritant. And if fiber intakes jump suddenly, gut bacteria, if they don't have the tools to ferment it efficiently, and this could lead to bloating, to gas, to abdominal discomfort. And in some people, actually leads to measurable increases in gut inflammation markers. That doesn't mean that fiber was the problem, it just means that your gut wasn't prepared. Another important reality is that people are just not consuming enough fiber. Like I mentioned, 14 grams per day for the most Canadians, where we should be getting 14 grams per thousand calories consumed. Now there's a huge gap, and that gap matters. So jumping from very low fiber intake straight into high fiber eating can cause problems. And often this is where frustration starts, and that's where people say, I I simply can't digest beans or broccoli or I can't eat more plants, just disrupts my stomach. Most people just start too quick. Now, there's also the concept of FODMAPS. I'll go through FODMAPS. Those are fermentable, other types of fermentable carbs that could potentially cause abdominal distress when they're increased at a high dose or too high of a dose in an untrained gut, much like fiber. And some people simply will have trouble with FODMAPS no matter how slow they try to increase, they hit a certain threshold where it starts to cause them problems. But that's not the goal of the episode today. We'll talk about FODMAPS at a in a future episode, but I want to keep talking about fiber because it matters and just increasing slowly for most people, it actually solves the problem. Now, for most people, if they increase fiber by a few grams every few days and kind of stretch the process of reintroducing more fiber across several weeks, within a few months your microbiome adapts, and what once caused you discomfort now becomes fuel for your good, beneficial bacteria. The gut barrier gets stronger and inflammation goes down. And this adaptation matters more than any single food choice. It's not about choosing a specific superfood, just increasing variety of different plants in your diet because they tend to be the biggest predictor of a healthy gut. Now, as I mentioned before, fiber is an umbrella term. It gets grouped into soluble and soluble, but there are other properties of fiber that matter: viscosity, fermentability, is it forming a gel? Is it bulking? Some fibers they slow down digestion, some fibers they get fermented super rapidly, and other pass through with minimal fermentation. So two people eating the same fiber amount will experience very different outcomes. One person could feel energized and more regular, and the other ones feel bloated and uncomfortable. This variability explains why fiber advice feels so confusing for a lot of people because there are different types of fibers with different types of properties, and we have different guts, and everyone's guidance should be different. And that's why it's so important to consider talking to a registered dietitian, someone who really is trained in gut health, and that tailors recommendations according to your history and your symptoms and your tolerance to these new foods. Now, the amount of fiber you consume matters, but also the type, but also the pace in which you increase. Now, just like exercise, this approach is pretty much identical. Start low, go slow, have personalized recommendations, progress, but do something that's sustainable over time. Now, before I wrap things up, I want to talk about a study done at Stanford by gut health experts Erica and Justin Sonnenberg. Basically, what they did is they took healthy adults that had a low baseline fiber and fermented food intake, and they randomized them into two diet groups. One group had a high fiber diet, and the other one had a high fermented foods diet. Now, both groups were guided to increase intake progressively, and basically they took blood and stool samples that were collected before, during, and after the intervention. Now, what was found at the end of that study was quite interesting. Participants who consumed fermented foods showed consistently an increase in gut microbiome diversity, and that's generally a marker that's associated with better gut health. Now, the fermented food group also experienced a broad reduction in inflammatory parameters in their blood, including multiple inflammatory cytokines. But on the high fiber group, that's where we found a few things that were interesting. Now, on average, looking at the whole group, those who consumed more fiber didn't actually show an increase in overall microbiome diversity. And levels of inflammatory proteins didn't decrease consistently for the group as a whole, as was expected. But an important nuance actually emerged when the researchers stratified participants according to their baseline diversity. So patients that had high diversity in their gut bugs at baseline tended to benefit from the high fiber diet. They showed signs of reduced inflammation, functional changes in microbial capacity to degrade complex carbohydrates. Basically, we had a gut that was more diverse and more able to break down foods. Whereas patients that had a low gut microbiome diversity at baseline, these patients did not show these same improvements. And in some cases, there were actually signals of persistent inflammation or what what they called a stalled microbiota response. Basically, without an established community of fiber degrading microbes, just adding fiber to it did not improve gut health. So if you do not have the bacteria to process the fiber, simply throwing a lot of fiber in your gut might actually make things worse. And that's because the benefits of fiber they depend on the presence of microbes that are capable of fermenting those fibers. And basically when they ferment those fibers, they ferment them into a ton of metabolites, including short chain fatty acids. Now, if an individual's microbiome or microbiota lacks these fiber degrading organisms, or if they have low numbers or a low diversity of these good gut bugs, then adding fiber can actually be harmful. Now, how to interpret this study is that fiber generally is beneficial for gut health, but its effect can vary by individual microbiome. It depends on the microbiome's capacity to ferment fiber. Now, fermented foods showed a more uniform benefit across the board in most participants, and the study just simply highlights the importance of personalized nutrition rather than simply assuming that any and every intervention will work for everyone. So, most important thing here to keep in mind is if you are going to believe in fiber and believe that it can help you, your success depends on having a strategy. Now we know that higher intakes will lower risk of cardiovascular disease, cancer, type 2 diabetes, cholesterol, high blood pressure, but you need to have a plan. And typically it looks like something like start low, go slow, build gradually, wait for your gut to adapt, your microbiome will grow stronger, inflammation will start to settle, and over time your gut will become healthier. A healthier gut is a gut that has a wide diversity of bacteria that are a part of the microbiome, that are efficient to process and to ferment fiber and other compounds you eat, and to reward you with beneficial postbiotics like short chain fatty acids. Now, start low, go slow is my motto when it comes to Medication or changing your exercise, and it's the same with fiber. Fiber only exists in plants. I tell my patients, try to count colors instead of counting calories, because with fiber, it increases the bulk of the food, the volume of the food, it decreases calorie density, it tends to make you fuller for longer. Other things that fiber can do, it can induce what they call the ilial break, meaning that it actually decreases calorie consumption at the next meal, makes a whole lot of magic of fiber. So, most important thing, get it from real foods because it comes in a matrix of fiber and phytochemicals and minerals and vitamins, and you get the benefits of all of these when you eat high fiber foods. Cool. Right on. I hope this makes sense. Fiber is good for you. Take your time. We have studies showing that for some people on an untrained gut, it could actually backfire, and that might make people retreat from any fiber-rich, nutrient-rich plant foods. Right on. Thanks so much for listening. You have an awesome day. We'll see you at the next episode. Peace. Hey everyone, go check out my website, plantbased drjouls.com, to find free downloadable resources. And remember that you can find me on Facebook and Instagram at Dr. Jules Cormier and on YouTube at Plantbase Dr. Jewels.