How Fiber Alters Gut Immunity

Symbiosis: the interaction between two different organisms living in close, physical association and to the advantage of both.

A healthy gut, in a person enjoying a balanced diet, is full of friendly bacteria living with its human in symbiosis. These bacteria live in one area — the large intestines — and take up camp close to the intestinal lining. They provide benefits to us, like producing vitamins, preventing against invaders, and using energy stored in food scraps to release substances that protect the cells of our gut from the inside out.

Bacteria Thrive on Fiber

After much of the nutrients are pressed, squeezed, and carried away from what we eat or drink, the bulk of what is left is fiber. Which is the favorite food for healthy gut bacteria. Such symbiosis! We eat the good stuff (think whole grains, fruits, vegetables, nuts, seeds, bean, legumes), and the fiber that we cannot digest is worked on by our bacteria buddies.

If our diet does provide enough food for a strong community of healthy gut bacteria, we can experience a range of issues, from indigestion and acid reflux, to anxiety and depression (more on this below), to irritable bowel syndrome or even colon polyps that may lead to cancer.

A Healthy Gut Plays Defense

Not only is it important to have healthy gut bacteria, it is important that bacteria stay in their place. The lining of the intestines is a barrier against invaders, keeping harmful bacteria, parasites, fungi, and yeasts out of our bloodstream. The gut is coated in a protective mucous secreted by specialized cells within the lining. Good bacteria live near the walls of the intestines, and add to the line of defense against germs. Finally, the gut also has a special immune tissue network called GALT (gut-associated lymphoid tissue), which is made up of a variety of white blood cells and patches of immune system tissue that release protective white blood cells and enzymes to prevent overgrowth of invaders. That’s how important the barrier is — there are back ups on back ups to protect and serve us.

Certain factors weaken the intestinal lining (like not eating for extended periods of time, critical illness, antibiotics, chronic intestinal inflammation, or a chronic low-fiber highly-processed diet) that can lead to the death of good bacteria, or allow them to move up the GI tract or even break past a weakened intestinal lining and enter the bloodstream. If the bacteria reach our blood, that’s when the good turns bad and things get rather Wild West. This is very undesirable.

Fiber and GALT

Research, lots of research, tons of research, shows that eating plant fibers improves GALT function along the 30-feet of our intestines, strengthening the barrier between the intestinal lining and our bloodstream. Specifically, fermentable fiber, also called “prebiotic fiber,” is what we seek. We say “prebiotic” because this fiber feeds the probiotics AKA good bacteria. Fibers of this sort have been shown to stimulate gut immunity.

Fermentable Fiber

Fermentation of fiber in the gut, by our friendly bacteria, is a healthy process that releases gases and acids which are able to help the body prevent or heal from inflammation, calm our nerves, improve mood, balance blood sugars and cholesterol levels, control appetite, prevent certain cancers, encourage absorption of minerals like iron, calcium, and magnesium, and just like, turn our bodies into magic vessels of life.

Top sources of fermentable fiber: All the fruits and vegetables (be sure to eat the peel), legumes, grains, nuts and seeds contain some amount of fermentable fiber. So its no wonder that a plant-based diet is associated with longevity and disease prevention.

Some foods that are particularly rich in fermentable, prebiotic fibers, are: apples, artichoke, asparagus, almonds, avocado, bananas, beets, butternut squash, cabbage, cashews, cauliflower, dark green leafy vegetables, dried beans, flaxseed, garlic, green tea, honey, leeks, onion, okra, pistachios, pears, dried peas, stone fruits, sweet potato, watermelon, and whole grains.

Focusing on a fiber-rich diet is an excellent way to prevent and manage illness.

Side Note: A Healthy Gut is a Happy Human

Of course, a healthy gut is more than just a passageway for food or a cozy home for bacteria. For example, intestinal tissue is a major producer of mood-balancing neurotransmitters, specifically serotonin. The friendly bacteria we feed by eating fiber-rich foods also produce serotonin, glutamate, and GABA — creating a conversation between the gut and brain that is called the gut-brain axis, and begins to explain why a number of mental health issues and psychiatric disorders are seen in people with chronic inflammatory intestinal disorders (Mazzoli and Pessione, 2016). A healthy gut with good bacteria is associated with lower anxiety, fewer neurotic behaviors, and reduced stress levels. Food for thought!

Published by Okay to Eat

Natasha Eziquiel-Shriro, MS, RDN, CDN

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