There’s a peculiar situation that is believed to develop when bowel flora are deprived of prebiotic fibers: They consume the mucous lining of the intestinal tract.
In other words, bacteria that reside in the intestines need to “eat.” They therefore depend on fibers, i.e., polysaccharides, that you ingest. (All fibers, regardless of type, are polysaccharides.) Humans lack the digestive enzymes to break down fibers, regardless of variety, that are therefore either consumed by bacteria or pass through the gastrointestinal tract and lost in bowel movements.
The variety of fibers consumable by microorganisms are called prebiotic fibers. The prebiotic variety of fibers make their way down to the colon where bacteria that have the enzymes necessary to digest these fibers metabolize them to the fatty acids, acetate, propionate, and butyrate. Butyrate in particular provides substantial health advantages to the human host, mediating improvements in insulin responsiveness, blood sugar, reduced triglycerides, reduced LDL particle number, reduced blood pressure, healthier intestinal lining, better sleep, less anxiety, better mood. The health benefits of prebiotic fibers is a recent discovery of major health importance.
Importance of the mucous lining
The human gastrointestinal tract provides the interface between the human body and components of the outside world that are ingested, whether water, fats, proteins, nutrients, or toxins. The entire length of the human gastrointestinal tract is lined with mucous, actually mucopolysaccharides, a mixture of proteins and polysaccharides that provides one of the first barriers of the gastrointestinal tract. Mucous provides a variety of functions such as protection against invading pathogenic bacteria and fungi, a barrier against potentially toxic compounds, as well as simple lubrication. The mucous lining is critical to intestinal and overall health, as without it, colitis, widespread inflammation, autoimmune diseases, colon cancer, and eventually death occurs. Animals bred to be unable to produce intestinal mucous die within weeks.
Mucous also protects the gastrointestinal tract against factors necessary for digestion such as hydrochloric acid produced by the stomach lining or bile acids produced by the liver. Unprotected exposure to either would be extremely destructive and result in self-digestion. Under normal conditions, mucous thereby provides a layer of protection to allow digestion of food components to proceed without damaging the gastrointestinal lining.
Mucous is produced by the so-called goblet cells of the gastrointestinal lining. Some species of bacteria inhabiting the colon also contribute by manufacturing mucous, as well as some species that trigger increased mucous secretion from human cells. Mucous is also used by some bacterial species as nourishment, especially when prebiotic fibers or other nutrients are in short supply. The unique bacterial species,Akkermansia muciniphila, and several species of Bacteroides are able to do so, consuming human mucous when preferred nutrients are unavailable.
We can view Akkermansia as a foundational species (meaning it is a crucial inhabitant of the human gut whose presence supports the growth of other beneficial microbes), that, as its name suggests (mucin + phila = mucous-loving) consumes the mucous of the intestines and is normally among the most beneficial of bacterial species. Akkermansia has been associated with improved insulin sensitivity, reduced blood sugar, and reduced visceral fat in both observational and clinical studies.
But consume a diet with too little prebiotic fibers and something odd happens. Microorganisms, like all other living creatures, have evolved to survive even when conditions are imperfect or undesirable. When there are no prebiotic fibers available, some bacterial species turn to the mucopolysaccharides of the intestines, i.e., intestinal mucous, for nutrition, while those incapable of consuming mucous are reduced in number, become quiescent, or die. Under conditions lacking prebiotic fiber, mucous-consuming species such as Akkermansia muciniphila will therefore thrive. Not only will this species survive on human mucous, but their number will increase substantially, likely due to the competitive edge its mucous-consuming capabilities provide. Several other bacterial species have been associated with this effect, also, when deprived of prebiotic fiber including several species within Bacterioides that, when prebiotic fibers are available, are anti-inflammatory and strengthen the intestinal barrier; when fiber-derived, they degrade and thin the mucous lining, promote inflammation, and weaken the intestinal barrier.
When prebiotic fibers are lacking, Akkermansia and several other mucous-digesting species will therefore markedly thin the mucous lining. We know from a variety of experiences that thinning of the mucous lining is a distinctly unhealthy phenomenon that promotes intestinal inflammation, increases intestinal permeability that allows unwanted substances to both contact the intestinal lining as well as enter the body, and further alter the composition of bowel flora.
These are among the reasons why, in the Undoctored Wild, Naked, Unwashed program, we pay special attention to our intake of prebiotic fibers, a daily practice that we all need to remain mindful of much more than, for example, intake of calories or vitamins. While plenty of attention is paid to probiotics, prebiotic fibers are at least, if not much more, important. For more on this important aspect of health, see the full discussion that I’ve posted in our Undoctored Inner Circle.