Is Your Gut Starving for Fiber? Fiber Myths Busted by “The Gut Health MD”


By Will Bulsiewicz, MD, MSCI, board-certified, award-winning gastroenterologist, and New York Times bestselling author of Fiber Fueled: The Plant-Based Gut Health Program for Losing Weight, Restoring Your Health and Optimizing Your MIcrobiome


Did you know that 97 percent of us consume an excess of protein, yet we still constantly ask, “Where am I going to get my protein from?” We live in a country with a pathologic protein obsession. Meanwhile, we are figuratively and literally starving for fiber. “Starving?” you say. “In this country? Where nearly three in four are overweight?” Absolutely. Your gut is completely FIBER STARVED. Imagine your gut as a dried-out, post-apocalyptic wasteland, with a lone tumbleweed rolling through. That solitary tumbleweed represents your fiber! Less than 3 percent of Americans get even the recommended minimum daily intake. That means 97 percent of Americans are not receiving the minimal daily recommended amount of fiber, let alone what I would characterize as optimal. Of all of the essential nutrients, this may be our greatest, most prevalent deficiency. Yet, we’re not talking about it and no one seems to be concerned. Enough with the protein obsession; it’s time we turn our attention to the vital question: “Where am I going to get my fiber from?”

Less than 3 percent of Americans get even the recommended minimum daily intake. That means 97 percent of Americans are not receiving the minimal daily recommended amount of fiber...let alone the optimum. — @theguthealthmd Click To Tweet

Fiber, the phoenix: Let’s burn it down and watch it come back stronger!

Okay, taking it from the top: What is fiber? In nature, fiber is a part of the plant cellular structure. Plants have a total monopoly on this nutrient. So if you want it, there’s only one way to naturally get it: from plants!

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From a nutritional perspective, fiber is a carb—it’s what we would refer to as a complex carbohydrate. If you take multiple sugar molecules and link them together, you’d get fiber. That doesn’t mean it behaves like sugar by any means. It doesn’t. Digestion of refined sugar starts in the mouth and in about twenty minutes it’s already been absorbed in the small intestine. Meanwhile, fiber remains unblemished as it passes through your mouth, stomach, and even fifteen to twenty feet of small intestine so that by the time it reaches your colon, it’s the same molecule that went in your mouth.

Two of the biggest myths about fiber are that all fiber is the same and that it does nothing more than go in one end and shoot out the other like a torpedo. Let’s dig deeper.

Myth #1: All fiber is the same, and all you have to do is count grams.

You’ve been taught that all fiber is created equal—that whether it’s in your breakfast cereal, the milky powder your grandma drinks, or in a granola bar, all forms of fiber are interchangeable. All you need to do is count the number of grams and you’re good to go. What you’ve been told is dead wrong.

The source of the fiber you eat is critically important. The fiber in your cereal or breakfast biscuit is not the same as the fiber in your quinoa. This is conceptually similar to how the source of our fats and our protein determines the impact on our microbiome. It’s an oversimplification to reduce fiber to a number of grams and pretend that all grams are created equal.

We’ve been taught to count grams of fiber for two reasons. One, it’s easy, and we like easy. And two, we have no clue how many types of fiber actually exist in nature. It’s incredibly difficult to analyze the chemical structure of dietary fiber, and there are four hundred thousand plants on our planet, three hundred thousand of them being edible. So there must be hundreds of thousands—if not millions—of types of fiber in nature. But we haven’t gotten around to figuring them all out yet.

Given the complexities in analyzing dietary fiber, we’ve simplified it by saying there are two basic forms of dietary fiber: soluble and insoluble. You can tell which is which by submerging the fiber in water. If it dissolves, it’s soluble. If it doesn’t, it’s insoluble. While I will occasionally make references to the difference between soluble and insoluble fiber, just know that in both cases we are talking about huge categories of fiber and that most plants contain some mix of both.

Myth #2: That fiber just passes through us.

If you do a quick Google search on fiber, you’ll find the general health benefits of fiber: It contributes to fantastic bowel movements by correcting diarrhea and constipation and increasing the weight and size of your bowel movement, lowers cholesterol, and controls blood sugar. These are all great things, and we should be celebrating these health benefits of fiber, for sure! But at the same time, we have been doing the undersell of the century here, folks.

We’ve all been taught that fiber pretty much goes in the mouth and out your . . . well, you know, and along the way, it sweeps some stuff out. And while there may be some truth to these statements, we’re being excessively simple about an incredibly complicated nutrient. So let’s take a closer look.

We humans lack the ability to process fiber by ourselves. Sure, we’ve got some enzymes called glycoside hydrolases that help us break down complex carbs, but we only have seventeen of them—just seventeen!—and none of them are designed for breaking down the larger molecules like fiber. In other words, we big strong humans are literally incapable of processing fiber on our own.

Now, if we lived encapsulated in a sterile bubble free from bacteria, we would never know the true power of fiber. But we get by with a little help from our friends. Because guess where you can find lots and lots of fiber and complex carbohydrate-processing enzymes? Yes, in our gut microbiota. Compared to the shockingly inadequate seventeen that belong to us, our gut microbiota may contain upward of sixty thousand of these helpful enzymes.

The fact that our microbiomes contain this insane number of digestive enzymes makes sense when you remember that there are three hundred thousand edible plants and potentially millions of types of fiber in our diet. By outsourcing fiber digestion to our microbes, we are taking advantage of their adaptability. Every single plant, every single type of fiber requires a unique team of microbes working in concert to get the job done. It’s demanding work, but what follows is magic. The breakdown of fiber by gut bacteria unleashes what I believe is the most healing nutrient in all of nature: (*Drumroll, please!*) short-chain fatty acids (SCFAs).

Learn more about fiber and SCFAs in Dr. B’s New York Times Bestselling book, FIBER FUELED.



From FIBER FUELED by Will Bulsiewicz, published by AVERY, an imprint of Penguin Publishing Group, a division of Penguin Random House, LLC. Copyright © 2020 by Will Bulsiewicz


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