Hemicellulose: The Dietary Fiber in Plants

Hemicellulose: the fiber in plants.

Hemicellulose is defined as the group of polysaccharides that are found in plant cell walls and present in commercially produced products made from corn grain hulls. These plant cell wall polysaccharides act as fiber when ingested by humans, and can help improve our health dramatically, as most people in the modern world are not getting enough fiber. This article details the types of dietary fibers out there, where hemicellulose falls on the fiber spectrum, and why we need fiber to avoid certain health conditions.

The Different Types of Fiber

First up, a fiber review: the good, the bad, and the functional.

Fiber can contribute to the health of your gut bacteria and help with weight-loss efforts. It is indispensable to a human diet, even in cases of serious gut disorders like IBS, Crohn’s disease, and ulcerative colitis; fiber-restricted diets are temporary and should only be done under medical advisement, and even then it’s almost impossible to eliminate all fiber from your diet.

Still, there are different kinds of fiber in our food, some for us, some for our gut bacteria, and some more beneficial than others. This section reviews the different types of fiber.

How Fiber Is Classified

Fiber is the umbrella term for a kind of carbohydrate that we humans cannot digest. That means that when we consume fiber, our digestive enzymatic processing can’t break it down, and it travels through the entire digestive system largely unchanged. Fiber is found in many plant materials, including plant foods like fruits, vegetables, whole grains, legumes, seeds, and nuts. From these plant foods we get two main types of fiber:

  • Dietary fiber: Fiber that is present naturally in our foods.
  • Functional fiber: Fiber that is extracted from whole foods, isolated, and then added into processed foods for various health or consistency reasons.

How does one or the other affect your well-being? We’ll have to go into greater detail to explain.

The Dietary Uses of Fiber

A few other ways to further classify fiber include dividing it up based on fermentability (is it fermentable or is it non-fermentable), solubility (is it water soluble or non-water soluble), and viscosity (is it viscous or is it non-viscous).

Fermentable Fiber

Since we humans cannot digest fiber, by the time it makes its way through the digestive tract to the large intestine, it is almost entirely unchanged. However, it is not useless to us, because fermentable fiber is digestible to our good gut bacteria, those tiny microbes that help defend our bodies from invading infections and parasites.

Fermentable fibers can be used as fuel for some of our smallest defenders, and in fact that is what “ferment” means in this context: to digest. Fermented foods such as kimchi and sauerkraut contain healthy probiotic bacteria you can add to the microbiome of your gut, because they are foods that are already being actively digested by little microbes you want to add to your gut flora.

Eating fermented foods and fermentable fiber can add to and bolster your friendly gut bacteria. Those microbes, when well-fed, can then produce short-chain fatty acids that help protect the cells of your colon. Most fermentable fibers are water-soluble, but some of the insoluble fermentable fibers can function in these ways too.

Fermentable fibers include beta-glucans, guar gum, inulin, oligofructose, and pectins, and can be found in whole foods like beans and legumes. The only downside is that a byproduct of fermentation in your gut is gas, so flatulence may be an issue.

Water Soluble vs. Insoluble Fiber

Whether fiber can dissolve in water separates it into these two categories:

  • Water-soluble fiber: This fiber can absorb and blend with moisture in your gut, causing the fiber to take on a gel-like consistency. Water-soluble fiber helps reduce blood sugar spikes when consumed, protecting you from certain metabolic health risks like type 2 diabetes.
  • Insoluble fiber: Insoluble does not take on water and is not broken down during digestion. This is fiber that can add bulk to your stool, which can help it pass more comfortably and swiftly through your digestive tract.

Soluble fibers include: beta-glucans, gums, pectins, psyllium, and more, while insoluble fibers include cellulose and lignin. Many plant foods have different ratios of both soluble and insoluble fibers.

Viscous Fiber

A subset of water-soluble fiber, viscous fibers are those that become gel-like when mixed with water, not unlike how chia seeds absorb liquids and change consistency. Viscosity references the thickness of the substance, as honey is thicker and thus more viscous than water.

When you consume a viscous fiber, it stays longer in the gut, slowing down digestion and increasing feelings of fullness and satiety. This helps curb appetite and can help people in their weight-loss efforts, as seen in this review of studies that found that viscous fibers were the only type of fiber that reduced food consumption and led to weight loss in 44 various studies.

Viscous fibers include: beta-glucans, glucomannan, guar gum, pectins, and psyllium. Food sources of viscous fibers are asparagus, Brussels sprouts, legumes, oats, and flax seeds.

Hemicellulose: the fiber in plants.

The Definition of Hemicellulose

So, which type of fiber is hemicellulose and what can it do for your health? Here are the answers.

What Is Hemicellulose?

Cellulose is one of the insoluble fibers, and hemicellulose is similar to cellulose, although with a lower molecular weight. Hemicellulose is the term for the non-digestible plant polysaccharides that are made in the Golgi apparatus of the cell, and then transported to the cell walls of plants. Hemicelluloses are made up of monosaccharides like galactose, mannose, rhamnose, and five-carbon sugars like arabinose and xylose (aka d-xylose).

Hemicelluloses include beta-glucans, glucomannans, mannans, xylans, and xyloglucans, and these dietary fibers are insoluble in water but are soluble in alkaline solutions. They can be more or less fermentable depending on which one you choose.

Xylan, for example, is a hemicellulose with side chains of arabinose or d-glucuronic acid, and can come in both soluble and insoluble form depending on the source it’s extracted from. It is also difficult to ferment.

Hemicellulose Uses

If all the above definitions sounded like sci-fi gobbledegook, what about the uses of hemicellulose? Well, hemicellulose can be used in processed foods as a thickener, stabilizer, emulsifier, or as added fiber. They may also be part of prebiotic supplements (prebiotics being the food for your gut bacteria, whereas probiotics are active bacteria that get added to the mix when you consume them).

In non-food uses, the conversion of hemicellulose also occurs in the pulp and paper industry where a hemicellulase enzyme breaks down the hemicellulose in wood.

Hemicellulose: the fiber in plants.

The Basics of Plant Biology

If you remember anything from your high school biology class curriculum, you may not remember the difference between primary walls and secondary walls in plants, let alone what lignocellulosic biomass even is (if that term ever crossed your path at all). What you may remember are that plant cell walls are sturdy and shaped more-or-less like little bricks, whereas animal cell walls are round and irregular. Hemicellulose is part of what makes plant cell walls more rigid and square, and when it’s in the plant foods you eat, it brings dietary benefits to your good gut bacteria and overall digestive health.

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