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Boost your immune system with … fiber?

Eat your veggies: the oldest dietary advice in the book. But what happens when you don't eat veggies, or any fiber? This rodent study looks into what might happen to your gut.

Study under review: A Dietary Fiber-Deprived Gut Microbiota Degrades the Colonic Mucus Barrier and Enhances Pathogen Susceptibility

Introduction

A significant body of research points to fiber being useful for people with digestive ailments[1], impaired glucose metabolism, and high cholesterol, but is fiber useful for the average healthy person?

Researchers know that a diet rich in plant foods and fiber is associated with a more diverse microbiome[2]. This makes sense because people can’t digest and absorb fiber, but the bacteria in our guts can. They literally produce thousands of enzymes to break down polysaccharides, large carbohydrate molecules such as fiber and starch. Bacteria in our guts break down consumed fiber and produce short-chain fatty acids[3] that we can utilize. Some of these short-chain fatty acids serve important functions such as fueling the cells of the colon and modulating inflammation[4]. Thus, the bacteria and cells that line our intestines thrive when we consume a diet rich in unrefined plant foods. What would happen if we didn’t supply our little friends with the food they need? They turn to other sources of food.

One of these sources is the mucus layer that covers the gastrointestinal tract, shown in Figure 1. In our guts, there are specialized cells known as goblet cells that secrete a layer of mucus. This mucus layer acts as a shield that protects the intestinal lining from toxins and microbes. Most bacteria are unable to colonize or utilize this mucus as an energy source. However, some microbes can use the mucus layer as a source of energy.

Figure 1: Introduction to mucus layer

References: Muniz et al. Front Immunol. 2012 Oct.
Earle et al. Cell Host & Microbe. 2015 Oct.

If bacteria that can use the mucus layer as a source of energy begin to multiply, how would this impact the mucus layer and pathogen susceptibility? That is what this study looked to investigate: how fiber deprivation affects microbiota composition, mucus barrier status and pathogen susceptibility. This is an important topic to investigate further because previous studies in animal models have shown a connection between reduced dietary fiber and a thin colonic mucus layer. A thin mucus layer has also been found to cause intestinal inflammation and colon cancer[5] in rats. In this study, the researchers colonized germ-free mice with microbes that are found in humans and that have been studied well. They then compared the effects of a fiberrich (FR) diet to a fiber-free (FF) diet and a prebiotic (Pre) diet.

Fiber consumption promotes a diverse microbiome because most gut bacteria rely on fiber as a source of energy. However, some bacteria can use the mucus layer in our gut as a source of energy. In times of fiber deprivation, bacteria that use mucus are more likely to survive and proliferate while bacteria that use fiber are likely to decline. Very few studies have actually examined how fiber-deprivation would impact the microbiota and the mucus layer. This study investigated how microbes found in humans would adapt to a fiber-deprived environment.

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Other Articles in Issue #27 (January 2017)