Fiber and Your Gut Mucosal Lining

Millions of individuals experience gastrointestinal concerns with diarrhea and/or constipation. Challenges with gas and a noisy, rumbling gut are seemingly commonplace. Perhaps tummy troubles have left you with embarrassing accidents or the need to rush to the bathroom. Undoubtedly, somewhere along this path you have been told to increase your fiber intake. You may have thought about it, but haven’t followed through.

Your gut lining needs several things to stay healthy like beneficial flora, vitamins and other nutrients, and especially fiber. If your diet lacks fiber, your gut lining becomes thin and broken down, i.e. leaky gut syndrome or increased intestinal permeability. This literally opens the door to an imbalance with unhealthy germs and immune challenges that can ultimately affect your whole body. The results of a fascinating descriptive study and other confirming studies may finally convince you that fiber intake is incredibly important to gut health.

Breakthrough Study

The breakthrough 2016 study entitled “A Dietary Fiber-Deprived Gut Microbiota Degrades the Colonic Mucus Barrier and Enhances Pathogen Susceptibility” delved into detailed analysis of what happens to gut health when dietary fiber is limited. The findings are stunning and open the door to significant understanding of gut health, which hopefully compels you towards increased fiber intake.

In this study, germ-free mice were inoculated with several strains of human gut flora. Mice were fed either a fiber-rich or fiber-free diet mimicking common dietary trends in industrialized countries. The outcomes demonstrated positive and negative changes to the gut flora and mucosal lining based on dietary fiber intake.

Bacteria Breakdown Mucosal Lining with Lack of Fiber

Results showed that mice fed the fiber-free diet experienced significant detrimental changes to gut flora. In particular, the bacteria Akkermansia muciniphila and Bacteroids caccae multiplied and expanded beyond their normal limited presence. These bacterial species can break down the gut mucosal lining as their food source when fiber is limited. Simultaneously, beneficial gut flora that helped breakdown dietary fiber decreased in number, which further disrupted gut flora balance.

Mice fed a fiber-rich diet had an intestinal mucosal barrier that was five times thicker than mice fed a fiber-poor diet. Those on the fiber-free diet developed a very thin mucosal barrier because the gut flora used the mucosal lining as their nutrient source. Thinning of the mucosal lining also led to immune challenges and provoked substantial inflammation throughout tissues.

Increased Susceptibility to Germs

The same groups of mice were further exposed to a germ challenge with Citrobacter rodentium. By day two, levels of the unhealthy pathogenic bacteria were ten times higher in the fiber-free group than fiber-rich group, i.e. enhanced pathogen susceptibility. The group with a fiber-rich diet, which had the thick healthy mucosal barrier, blocked the pathogen from entry and stopped further inflammatory destruction. The fiber-free group, however, experienced markedly higher levels of bad bacteria attaching to and penetrating the gut lining, which led to disease and increased mortality rate.

Scientists found that even variations of fiber intake between intermittent low intake and chronic low/no fiber diets readily changed the gut mucosal barrier thickness and risk for germ invasion and inflammation.

Gut Lining Changes Quickly in Response to Diet

A subsequent study published in 2019 showed that after only 3 days of a low-fiber diet, there was marked adverse thinning to the gut mucosal barrier, an increase in unhealthy flora, and much greater likelihood of germs penetrating the gut lining. The result was a highly inflamed gut. Think about the last time you let your diet slip when you did not have access to quality fiber-rich foods, how did your gut feel after just a few days?

Societies around the world that follow the Western diet with high calories, processed foods, and decreased fiber intake, have seen a marked uptick in inflammatory bowel problems. These findings provide further information to encourage increased dietary fiber intake.

Mucosal Barrier Importance Summary

Your gut flora needs soluble and insoluble fibers to survive, thrive, and stay in a healthy balance. If flora does not have enough fiber to survive, they turn to the next food source, i.e. the mucosal barrier. The gut mucosal barrier is a physical barrier that protects the thin epithelial lining against germs that are naturally present in your gut and those that arrive through ingestion of food, water, etc. The gut mucosal barrier also contains a storehouse of things like antimicrobial peptides and immunoglobulins, which act as a first line of defense against germs.

When fiber is missing from the diet, gut flora remodel into a state of dysbiosis, i.e. an imbalance of pathogenic and/or non-beneficial germs that crowd out beneficial flora. This effect creates irritation, inflammation, and oxidative stress that makes you more prone to significant digestive disorders. It further stresses and depletes your storehouse of other beneficial immune protecting compounds.

Ultimately, inadequate fiber leads to breakdown in the mucosal lining (leaky gut syndrome), erosion of the gut barrier, and increased likelihood of gut infections. Poor gut health eventually creates systemic effects throughout the body with aches, pains, dysregulation with blood sugar, cholesterol, obesity, and affects brain, thyroid, skin, immune, lymph, gallbladder, and liver health etc.

What’s Your Fiber Trend?

Everyone knows you need dietary fiber. It seems like a redundant suggestion when you want something to help your gut health. Dietary or supplemental fiber does not have the same appeal as a quick-fix drug to amend digestive concerns. You may also think fiber supplements are needed only by the elderly. The reality is that many individuals of all ages do not consume adequate fiber or come close to the recommended daily intake of fiber.

Consider your daily habits. If you juice your fruits and vegetables, picture the finished product. By throwing away the pulp that is left over from juicing, you are missing out on the fiber. If you follow a Paleo-, keto-, grain-free, or gluten-free diet, or consume the typical Standard American Diet, fiber intake will be lacking. If you eat only once or twice a day, eat on the go, or have a lot of take-out, chances are you are not getting enough fiber. If you avoid fruits and vegetables, seeds, and nuts, you are missing out on fiber-rich foods.

Think about your children or grandchildren with fussy taste buds and a preference for fast foods and processed products rather than whole grains, fruits, and vegetables. Factor in antibiotic use, acid blocking drugs, and other medications that disrupt gut flora. Is it any wonder gastrointestinal concerns are so prevalent? Compared to other countries with non-Westernized diets, we now consume up to 7 times less dietary fiber than they do. This is a massive factor in the increased prevalence of gastrointestinal concerns and impacts health and metabolism in all other body tissues and organs.

Fiber Intake

The Institute of Medicine recommends that adult men consume 30-38 grams of fiber per day. Women require 21-25 grams of fiber per day. The Standard American Diet often contains a paltry intake of less than 15 grams of fiber per day. You can readily calculate your daily grams of fiber intake by reading labels on your packaged items. There are also websites, like the National Agricultural Library USDA, and phone apps that you can use to calculate fiber amounts in food. Here is a sample diet to compare.


Orange juice, 6 ounces, with pulp 0.5 grams
Toast, one slice 100% whole wheat 2 grams
Two eggs 0 grams
One banana, medium 3 grams
One cup coffee 0 grams

Spinach, raw, one cup 0.5 grams
Cherry Tomato, one cup 1.8 grams
Cucumber, raw, peeled, one ounce 0.9 grams
Chicken, 3 ounces, unbreaded 0 grams
Almonds, roasted, one ounce 3.3 grams

Spaghetti, whole wheat, cooked, one cup 6 grams
Meatballs, three ounces 0 grams
Broccoli, one cup, cooked 5 grams
Carrot, one medium, raw 1.5 grams
Brownie, box mix, one ounce 0 grams
Raspberries, fresh, one cup 8 grams

Total fiber 32.5 grams

Two Lifestyle Challenges for You

As we head into late fall and winter seasons that are often filled with goodies and sedentary behavior, I ask you to take on two lifestyle challenges. The first challenge is to increase your fiber intake to at least 25- 35 grams per day. If you already consistently consume 25 grams per day increase it to 35 grams or higher per day. Our ancestors consumed at least 2-4 times more fiber than this. Increase fiber intake gradually from fiber-rich foods. Make sure to increase your water intake by at least another 12 ounces per day, or drink a minimum of 8 x eight ounce glasses per day.

Consider a fiber supplement like Fiber Helper with oat beta glucan, psyllium, and arabinogalactan to help when your diet lacks fiber or you want something easy and that tastes good. If your mucosal barrier has thinned, or literally been eaten away by your gut flora from lack of fiber, you will have health problems. You need to be very proactive about gut restoration.

The second challenge I give you is to make sure you are physically active every day. If stay-at-home orders and further lock downs occur as government agencies warn, this action combined with forthcoming cold winter temps, snow and ice will dampen physical activity for many. Walking is a great start. Strive for 10,000 steps or more per day. If you can only do 2000 steps now, work your way up to 10,000 adding 200-500 steps per day as you tolerate it. Walking and physical exercise healthfully changes the gut microbiome. It improves the diversity of the flora and supports compounds that help make the mucosal barrier.

Just a few decades ago, fiber-rich diets and active lifestyles were commonplace. With modernization and processing of foods, sedentary desk jobs, and other cultural changes, the Western Diet and lifestyle has led to loss of these basic principles and with it a decline in health. Embrace the challenges. Increase your fiber intake. Bring back the morning constitutional walk after your fiber-rich breakfast. See how your digestive tract feels with these changes. You may be pleasantly surprised!

Additional resources:

Oat Beta Glucan – Nature’s Heart Healthy Wonder

Fiber Sets the Foundation for Healthy Weight Loss

Fiber, Leptin, and Weight Loss 

Healthy Poop: What is Your Digestive Tract Telling You? 

Top Essentials For Daily Health – What’s Your Health Trend? 

A Lifetime of High Fiber Intake Reduces Cardiovascular Disease Risk

Low Fiber in Teens  

Higher Fiber Prevents Weight Gain and Abdominal Fat Gain

The Leptin Diet Weight Loss Challenge #1 - Overview and Basic Needs 

Psyllium Reduces Digestive Food Craving Signals

Exercise Endurance and Energy Linked to Gut Health