As the interest and importance of the microbiome grows, so do the studies looking into all of these wonderful connections. One recent study, in particular, took this research to the next level and delved into the relationship between the different types of fiber and how they each affected the health of our microbiome.

The microbiome’s primary source of food is fiber, meaning different types of fiber may actually affect the overall health and ecosystem of your microbiome. Since not all fiber is created equal, the study looked at the best sources of microbiota-friendly fiber, as well as how different fibers affect the bacteria.

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Gut Microbiome 101

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Before we dive into the relationship between fiber and your microbiome, it’s probably a good idea to figure out what your microbiome actually is.

First off, let’s clear the air of verbiage: microbiome versus microbiota.

Microbiota is the term used to identify the “collection of microbes that live in and on the human body,” while the microbiome “refers to the complete set of genes within these microbes. Simply put, “one refers to the entirety and the other refers to the individual or more detailed version of the former.”

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Alright, now what’s the microbiome?

In the One Green Planet article Understanding the Gut-Hormone Connection, I take a quick 101 on microbiome:

“The microbiome is very similar to a ‘mini-ecosystem’ in which microscopic organisms thrive. These microscopic organisms, also called microorganisms, create a symbiotic environment called the microbiome and they include ‘bacteria, pathogens — infections agents, — archaea — prokaryote microorganisms, which lack a nucleus, — and eukaryotic microbes — microorganisms that have a nucleus.’ Your microbiome is built from your personal environment and lifestyle, such as ‘geography, health status, stress, diet, age, gender, and everything you touch,’ therefore every human’s microbiome is special and unique to them.”

Types of Fiber

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When you think of fiber, your mind may go directly to things like whole grains, oats, and flax seeds. Yes, these are excellent sources of fiber, but what type of fiber? When referring to getting “fiber” in your diet, there’s actually a “huge variety of different fibers found in foods,” so it’s probably a good idea to figure out what these are and which ones you really want.

As with most things in life, it gets a bit more complicated before it gets simpler!

Fiber is classified into two different groups, dietary fiber and functional fiber. Dietary fiber is the type that you find naturally in the foods you eat, while functional fiber is “extracted and isolated from whole foods, then added to processed foods.”

Up next, these classifications are broken down into the design of fiber: insoluble versus soluble. Insoluble fiber is known as the “bulking” agent of the body as it “does not blend with … water and passes through the digestive system mostly intact,” helping to bulk your stool and keep you from becoming constipated. Soluble fiber on the other hand “blends with water in the gut, forming a gel-like substance” and this type of fiber is also that miracle substance that can “reduce blood sugar spikes, and has various metabolic health benefits.”

Alright, we’ve got classifications and we’ve got a design, how about the specific types?

Well, you could break these categories further into fermentable fiber — “fibers that the friendly gut bacteria are able to digest (ferment) and use as fuel” and viscous fiber — “soluble fibers [that] form a thick gel when they blend with water,” but we’re gonna take it a bit closer to the actual foods and look at the basic seven types of fiber that you should probably know about!

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1. Cellulose

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Cellulose is an insoluble fiber and is “a primary component of plant cell walls, and many vegetables—such as broccoli, cabbage, kale, and cauliflower—are rich sources of cellulose.” This type of fiber is great for bulking the stool and it also “keeps the digestive system healthy by aiding the growth of beneficial gut bacteria.” Along with the mentioned veggies, you can find cellulose in “legumes, nuts, and bran.”

2. Inulin

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Inulin is a soluble fiber which “isn’t digested or absorbed in the stomach — it actually sets up shop in the bowels, promoting the growth of beneficial flora associated with improving gastrointestinal (GI) and general health.” Plus, inulin plays a double role because it’s also a fructan, “which is very fermentable by our gut bacteria,” but that also means “some people might … experience GI distress,” depending on their specific sensitivity.

Inulin can be found in “chicory root, and naturally found in fruits and veggies such as bananas, garlic, onions, and asparagus, as well as in wheat (like barley and rye).

3. Pectins

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Pectins are oftentimes known as the powerhouses of the fiber family! Pectins are soluble fiber “that help reduce the glycemic response of foods by stalling glucose absorption,” which means this type of fiber can actually reduce blood sugar spikes. Magic! Well, not really, but seems like it. Plus, pectins are “well metabolized by our gut bacteria, and like other soluble fibers, may help to lower cholesterol by flushing fatty acids out of the body.”

Pectins also happen to be super easy to find such in foods like “apples, strawberries, citrus fruits, carrots, and potatoes, and in smaller amounts in legumes and nuts.”

4. Beta Glucans

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Beta glucan is a soluble fiber “that’s fermentable by our gut bacteria” and is considered a “prebiotic, providing ‘food’ for good gut bacteria.” This type of fiber is known to slow the food leaving the stomach, as well as the transit time within the intestines meaning it can help “in increasing satiety and managing blood sugar levels.” With that said, beta glucan fiber is a bit harder to find in the foods you eat, yet you can get a reasonable dose from “oats, barley, shiitake mushrooms, and reishi mushrooms.”

5. Psyllium

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Psyllium is a soluble fiber — meaning it’s great at relieving “constipation by softening [stool] to help it pass” — and it’s also a “handy gel that binds to sugars and helps to prevent reabsorption of cholesterol in the digestive tract.” Plus, this is yet another wonderful prebiotic “that feeds the friendly bacteria in the gut.” Psyllium isn’t actually found in other foods but is a fiber-rich food itself, which means “you’ll only find this type of fiber as a supplement or an ingredient added to other foods.”

6. Lignin

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Lignin and cellulose are very similar — both insoluble fiber and both make of the “cell wall structure in plants.” When it comes to lignin, research suggests “that insoluble fiber may help to reduce the risk of developing colon cancer.” On top of that, lignin is excellent at bulking the stool and decreasing the risk of constipation. Lignin is found in “whole grain foods (wheat and corn bran), legumes (beans and peas), vegetables (green beans, cauliflower, zucchini), fruits (avocado, unripe bananas), and nuts and seeds (flaxseed).”

7. Resistant Starch

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If you’ve been around the health world long enough then you’ve definitely heard about resistant starch. Yet, did you know it’s technically a fiber?

Resistant starch “functions similarly to soluble, fermentable fiber” meaning it helps “feed the friendly bacteria in the gut” by passing “into your large intestine, and together with your immune system and microflora, [helps] to guard against any pathogenic bacteria that attempts to mess with your GI tract.” Resistant starch has also been found to have a variety of other health benefits including aiding in weight loss by “taming appetite and blood sugar spikes,” increasing heart health “by lowering cholesterol,” and boosting digestive health “by keeping things regular.”

Resistant starch is actually quite common and can be found in legumes, beans, oatmeal flakes, and unripe bananas.

One Study, Various Fiber Sources, and Your Gut

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Alright, so there’s quite a few varieties of fiber out there in the nutrition world, so what should we look at when we’re aiming to boost gut health?

That’s a question the one study aimed to deduce!

Based at the Washingon University School of Medicine in St. Louis, Missouri, a team of researchers, “along with international collaborators,” sought to find out all they could about “microbiota directed foods … to improve our health.”

The study chose a large range of dietary fiber to study including “pea protein, citrus peel, citrus pectin, tomato peel, orange fiber, apple fiber, oat hull fiber, cocoa, chia seeds, and rice bran … [totaling] … 144 different diet combinations.” Each specific diet was then analyzed and observed reaction “to the presence of the various fiber sources.”

For instance, the researchers discovered that “B. thetaiotaomicron abundance increased in the presence of citrus pectin and pea fiber, while B. ovatus levels rose in the presence of barley beta-glucan and barley bran.” The study also found that foods high in resistant maltodextrin, molecular weight inulin, and psyllium “resulted in an increase in members of the Bacteroides strains.”

All-in-all, the researchers were delighted to find that the type of fiber ingested did in fact play a major role in the type of bacteria that grew in the gut.

Cooking with Fiber

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Now that you know all you needed to know about your gut and fiber, how about getting these foods into your body on a daily basis? One of the most important parts of fiber consumption is variety. Basically, try to get as many types of fiber into one meal, which will help hit all those wonderful fiber “marks” such as decreased blood sugar spikes, increased satiety, bulkier stool, and a boost in gut health! Luckily, there’s a host of creative and easy ways to make sure you’re feeding your gut microbiota. Here are a few ideas to get you started!

1. Black Lentil Charred Broccoli Shepherd’s Pie

This Black Lentil Charred Broccoli Shepherd’s Pie recipe by Stephanie McKinnie takes on the traditionally meat-based shepherd’s pie recipe with 100 percent purely plant-based and vegan ingredients. Plus, it mixes together some of the most powerful fiber-rich ingredients including broccoli, lentils, and onions. This is a perfect recipe to spend a bit of time on and then feast off of for the remainder of the week, meaning you’ll also get multiple doses of gut-friendly fiber!

2. Flourless Rhubarb Custard Cake

Out of all the fiber options, you’re probably curious about that psyllium. As it’s not a component but an ingredient, this may be one of the hardest to get on a regular basis, yet it’s truly a wonderful vegan baking agent to keep in your pantry. Psyllium is a wonderful gel-like binder that can replicate that stickiness of eggs, meaning you can substitute in a variety of recipes such as this Flourless Rhubarb Custard Cake recipe by Nele Liivlaid. Along with fiber-rich psyllium husk powder, this recipe also calls for fiber-filled chickpeas!

3. Matcha Avocado Smoothie

Avocado is a vegan-friendly powerhouse! It’s not only rich in fiber — 9 grams in one fruit — but it’s also packed with nutrients including monounsaturated fat, polyunsaturated fat, saturated fat, omega-3 and omega-6 fatty acids, vitamins (A, C, E, K, niacin, folate, choline), and minerals (calcium, magnesium, phosphorus, and potassium).

While there are a ton of ways to eat avocados — from raw out of the skin to fried like … well … fries — if you’re looking for super simple and on-the-go type recipes, try this fiber-rich Matcha Avocado Smoothie by Kat Condon. This smoothie not only has avocado and banana, but it also integrates fiber-powerhouses chia seed and hemp seed, plus a dose of energizing matcha powder!

We also highly recommend downloading our Food Monster App, which is available for iPhone, and can also be found on Instagram and Facebook. The app has more than 15,000 plant-based, allergy-friendly recipes, and subscribers gain access to new recipes every day. Check it out!

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