Updated: Jul 12
While everyone seems to be panicking about protein, or talking about carbs being the enemy and fat making you fat, I’m sitting here stunned at the fact that no one is talking about one of the most important nutrients of all: fiber.
Everyone seems to agree that fiber is good for you, but I really believe that most people don’t know to what extent fiber is associated with health and protection from disease. Unfortunately, the nutrient most associated with positive health benefits is considered a non-nutrient, since it can’t be broken down by our bodies. This important « non-nutrient » also seems to be the one most likely to be deficient in one’s diet. People assume fiber simply “goes right through you”. Both constipation and diarrhea are improved by increasing fiber, a fact misunderstood by many. Other avoid fiber because of associations with bloating, a decision many will live to regret.
Here, I’ll talk about fiber, what it is, what it does, and why I consider it to be one of the most important of all nutrients, not just for bowel movements, but for overall health. Although considered a non-nutrient, in my opinion, it does nourish the body and should be taken very seriously.
What Is Fiber Anyway?
Firstly, fiber is a complex carbohydrate, meaning it is a long molecule containing carbon, oxygen and hydrogen. What makes this specific carbohydrate special is that humans don’t have the enzymes to break it down. This means that fiber makes it all the way down the digestive track untouched until it reaches your colon. Guess who does have the enzymes to break them down… our gut bacteria! For them, it’s their favorite food and they ferment fiber to produce all sorts of compounds with benefits for human health. These magical compounds do much more than just help bowel movements. We’ll get back to these shortly!
The Different Types
Not all fiber is the same and there are as many types of fiber as there are types of plants. The fiber in your apple is very different from the fiber in your quinoa and both have different properties and different health benefits. Each specific type of fiber feeds a different population of gut bugs, and this leads to various health benefits. Getting 30 grams of fiber from one single food source is better than nothing, but not recommended if overall health is what you’re looking for. If health is your goal, aiming for plant variety, in order to achieve fiber variety, is the way to go. Given the fact that there are hundreds of thousands of plants on this planet, we assume that there are at least that many different types of fiber. Since analyzing all of those different types of fiber would prove to be impossible, we’ve simplified the classification process by grouping them in two large categories: soluble or insoluble, depending whether or not their dissolve in water. Fiber can also be fermentable or non-fermentable by bacteria, and can even be classified as viscous or non-viscous, depending on whether or not they form a gel-like substance substance when exposed to water (think of chia seeds).
Some compounds, like resistant starches found in underripe bananas for example, behave exactly like fiber and make their way to our colon where they are fermented by bacteria, to produce the same beneficial short-chain fatty acids that are produced through fiber fermentation. Resistant starches can also be found in whole grains, legumes and starchy vegetables.
People still think fiber is an inert substance that simply passes through our digestive system untouched. This couldn’t be farther from the truth. Although the human genome only has 17 glycoside hydrolase enzymes that break down the saccharide links in carbohydrates, the bacteria that reside in our gut have upwards of 60 000 of these enzymes. Fiber, other than contributing to awesome dumps and epic bowel movements, also contributes to lower rates of cancer and cardiovascular disease, helps lower cholesterol and helps control and stabilize blood sugar. If you think that encoding a gene for an enzyme for every single type of fiber out there is an inefficient way to use our complex genetic make up, you’re right. That’s why we’ve delegated this complex task to the bacteria in our gut that have evolved over millions of years, even long before we were here. Every single type of fiber is digested and fermented by a different combination of bacteria, which is why plant diversity is so healthy. Each type of bacteria digest a different type of fiber in a different way, producing a wide array of beneficial chemical compounds in return for the fiber we provide them.
Soluble fiber is generally fermentable and serves as a prebiotic (food for our gut bugs). Bacteria ferment it into beneficial compounds, like short-chain fatty acids. Types of soluble fiber includes beta-glucan (oats and barley), guar gum and psyllium. Psyllium is a soluble, yet non-fermentable fiber that creates bulk and improves bowel movements. Most soluble fibers slow down digestion, delay gastric emptying and provide an extended feeling of fullness, both via their effects directly on the digestive system and also via short-chain fatty acids that reduce appetite through their effects on the gut-brain axis. Regular consumption of foods containing soluble fiber has been shown to reduce cardiovascular risk, through their beneficial effects on LDL cholesterol and blood sugar.
Insoluble fiber does not dissolve in water and provides a bulking effect for stools. Cellulose and lignin are examples of insoluble fiber. Insoluble fiber helps maintain normal bowel regularity and function. The goal should always be to have a diet rich in foods containing a variety of types of fiber, including both soluble and insoluble types. You can achieve this by eating sa much plant variety as practical, including as many different colours as possible.
Fiber: Adequate Intakes
Almost 95% of the population doesn’t meet the recommended daily amount of fiber. Adult females should be getting at least 25 grams per day and adult males should aim for 38 grams or more. Food processing removes most of the fiber found in whole foods in order to make them shelf stable and to concentrate calories, for an increase in palatability, taste and profits. Animal products, including meat, dairy and seafood, contain zero grams of fiber, probably explaining why our modern diets are so fiber deficient. Studies show that even with recommended intakes of 25-38 grams, our ancestors probably consumed well over 70 grams of fiber per day, while other studies have suggested ancestral intakes of well over 100 grams. While you might be tempted to count grams of fiber, gut biodiversity seems to be determined mostly by plant variety, not grams of fiber. To reap the maximal benefits that fiber have to offer, aim for as many different plant types as possible more than a target number of grams. Count plants, not grams. Studies suggest that aiming for 30 different plant types per week is the best predictor of a healthy gut microbiome. This ensures that the maximal amount of gut bugs get fed. Since each family of bacteria produce a unique blend of chemical compounds, the variety, rather than total amount of plants you eat might be the way to go. By plants, I‘m referring to fruit, veggies, legumes, nuts, seeds and whole grains.
Fiber Benefits: The Microbiome
Our increasing knowledge of the role played by our microbiome is one of the greatest scientific advances of recent years. Over the last few decades, there has been exponential growth of our understanding in how fiber, resistant starches, polyphenols and omegas feed our gut bugs, which then produce beneficial compounds that promote health. To better understand the roles played by thsee compounds, let’s simplify it by reducing it to a simple equation:
Prebiotics + Probiotics = Postbiotics
Prebiotics include foods that feed our gut bugs and include fiber, resistant starches, polyphenols and some omegas.
Probiotics are the gut bugs themselves that feed on prebiotics. Most people recognize the term probiotic as the good bugs we’ve manage to package and sell as natural supplements either in pill or liquid form. Good gut bugs, or probiotics, include bacteria from species like Lactobacilli, Bifidobacterium and Prevotella. After Prebiotics are fed to Probiotics, they‘re fermented to produce beneficial chemical compounds we call Postbiotics.
Postbiotics are where the magic happens. These chemical compounds are produced after our gut bugs ferment fiber, resistant starches, polyphenols and certain omegas. Fiber fermentation leads to the production of the most important of all postbiotics, SCFA (short-chain fatty acids). Other important compounds are also produced through fermentation of the other prebiotics.
SCFA include three important compounds: butyrate, propionate and acetate. These chemical powerhouses have beneficial health effects right in the colon, where they suppress the growth of inflammatory and pathogenic bacteria, aka the bad gut bugs. They also promote thickening of our gut mucus layer, which provides further protection against pathogenic gut bugs and other harmful chemical compounds that can enter our circulation when the mucus layer is thinned or damaged. They also help fuel and heal colonocytes, which make up the single cell layer separating our circulation from the outside world. SCFA helps repair and build gap junctions, which are complex proteins that connect colonocytes together. Damage to gap junctions makes the colonocyte layer more permeable, which could make it easier for bacterial endotoxins to enter our bloodstream. This hyperpermeability or “leaky gut” is one of the main characteristics of dysbiosis, the term given to an imbalance in our gut microbiome’s good bug diversity. Butyrate, one of the SCFA, also improves gut motility and reduces gut hypersensitivity, two hallmarks of IBS that were detailed in a past blog post that you can access here. In your gut, postbiotics from fiber fermentation are able to improve motility, reduce gut permeability (leaky gut), fuel colonocytes and reduce dysbiosis. After fighting crime right in your colon, SCFA get absorbed in your bloodstream, where they’ll move on to bigger better things. I’ve dedicated a full section of my website to discussing the latest scientific evidence surrounding the microbiome. Access it here.
The Systemic Effects Of SCFA
Once SCFA have done their job locally in the gut, they then proceed to being absorbed in the bloodstream, where they’ll circulate in every nook and cranny of your body, sprinkling their magic everywhere they go. Here’s how fiber can lead to benefits outside of your colon. If you really want to nerd out on fiber and its link with our microbiome, you can access the section of my website that I’ve dedicated completely to our microbiome, here.
Is There Such A Thing As Too Much
Even though fiber has magical properties, over consuming it does come with some downsides. In growing children, overdoing it on fiber rich foods will reduce the caloric density of their meals, and could theoretically decrease their caloric intake to an extent where their basic caloric requirements aren’t being met. But let’s not forget that 95% of people, kids included, are getting most of their calories from fiber-depleted processed foods. Let’s just say that fiber deficiency is exponentially more common than fiber excess, but caution is still advised. Other people that could theoretically fall short of their caloric needs are athletes. Some expend upwards of 10 000 calories per week through physical activity and filling up on fiber rich food could potentially lead to insufficient calorie intake. Specific types of fiber, when eaten in excess, can even block the absorption of specific nutrients. For example, if you‘re eating excessive amounts of wheat bran, you might be getting enormous doses of phytates, which are known to inhibit the absorption of important minerals. As stated earlier, conditions like cardiovascular disease, cancer and immune-allergic conditions are rampant because of fiber deficiency, not excess.
A word of caution must also be spread to those in a rush to increase their fiber intake. It’s very important to remember that over time, your gut bugs adapt to your usual fiber consumption. Much like a beginner gym enthusiast would never squat 100 pounds their first day, increasing fiber too quickly might overwhelm a fragile and underpowered gut microbiome, leading to inefficient fermentation and pain, bloating and gas. Your microbiome will require 6-8 weeks to adjust, so that microbial numbers can increase and start to ferment fiber efficiently. Increase fiber slowly! Those who don’t are most likely to be the ones led to believe that they can’t “tolerate“ or digest legumes, or beans. If you identify yourself as not being able to properly digest fiber rich foods, the problem is more likely to be your own microbiome, not the food itself. Do yourself a favour and go read my recent blog on IBS, gluten and FODMAP foods. You can access the article here.
My Fiber Prescription
Fiber is found solely in plant foods and chances are you’re not getting enough. Microbial diversity is associated not only to fiber quantity, but to the diversity of plants in your diet. Aim to increase your daily consumption of fiber slowly, to avoid nuisance side effects like bloating and gas. Aim for at least 30 different plants per week, from various sources of fruits, veggies, legumes, nuts, seeds and whole grains. This will provide sufficient prebiotics to feed our beneficial probiotic gut bugs. In return, they’ll reward us with the magical properties of the postbiotic compounds they produce. Most of the modern day medical illnesses that plague us can be linked directly to our fiber deficient diets, and it‘s about time that fiber gets the attention it deserves. Fiber isn’t only useful for bowel movements. Those consuming higher amounts of fiber in their diets have reduced rates of cardiovascular disease, hypertension, cholesterol, cancer, auto-immune disease and many other serious conditions like diverticulosis and constipation. Don’t take fiber for granted. Everyone keeps talking about fat, carbs and protein, when many of our modern medical conditions can be traced right back to lack of fiber. I’ll leave you with words of wisdom from a great leader in the of plant-based movement, Dr Bulsiewicz: « Eat plants, take epic dumps », oh and prevent cancer, cardiovascular disease and many other of our most frequent diseases in the process.
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