Herath 2020

I discussed the importance of the gastrointestinal (GI) mucus barrier in my Super Gut book. But it is such an important issue for overall health that is rarely discussed that I thought it would be a good idea to discuss it further here.

Mucus is something that most people don’t think about too much. You may even regard it as a nuisance, coughed up, for example, during a respiratory infection, or blown out your nose during a bout of sinusitis. But mucus is an essential factor in human physiology and health. Without mucus you would not survive. Here we are going to focus specifically on the mucus lining the entire 30-feet of GI tract that is critical for your health. You are therefore about one millimeter of mucus away from gastrointestinal destruction and death, so let’s mind your mucus.

GI mucus performs several crucial functions, such as:

  • Lubrication—You swallow the chewed piece of steak or celery. If the esophagus and stomach did not have mucus, food material would get stuck, adhering to dry tissue. Without mucus, fecal material in the colon would likewise never make it out comfortably into the toilet.
  • Barrier-–There are many things that traverse the GI tract that would be damaging if they directly contacted the cells lining its length: partially-digested food, acids, bile, bacteria, bacterial breakdown products, fungi, etc. If or when such factors directly contact the intestinal lining, the GI tract becomes inflamed, can be damaged, and some factors are allowed to enter the bloodstream. Degradation of the mucus barrier is part of the basis for intestinal inflammation such as colitis, food intolerances, and autoimmune responses.
  • Immune mediator—Intestinal cells produce various anti-inflammatory factors: peptides, enzymes, and antibodies that protect intestinal cells from microbes and partially-digested food. Mucus therefore provides a semi-liquid vehicle for conveying such factors.
  • Nutrition for selected microbes—There are microbial species such as Akkermansia and Bacteroides thetaiotamicron that are able to consume mucus. This can be a good thing, but it can also backfire on us, discussed below.

We therefore pay attention and avoid factors that disrupt or dissolve the GI mucus barrier. Emulsifying or mixing agents, for example, such as polysorbate 80 and carboxymethylcellulose in commercial ice creams, or the polyethylene glycol of Miralax used as bowel prep prior to colonoscopy or prescribed chronically for constipation, are massively disruptive over the mucus barrier. Although such disruptions can be temporary, as mucus is produced continuously, even a few minutes, hours, or days of mucus disruption has an impact on health by altering the microbial composition of the GI microbiome, allowing direct contact of intestinal contents with intestinal cells, and increasing entry of various factors into the bloodstream, most notably bacterial endotoxin that transports adverse effects to all other organs of the body such as coronary arteries, skin, and brain.

Also, note that the composition of the mucus barrier is different in the various segments of the GI tract. One of the most important differences emerges in comparing the mucus lining of the 24-feet of small intestine vs. the 4-5 feet of colon. (See diagram above.) The colon has a thicker, more viscous, 2-layer mucus barrier and is therefore well-suited to dealing with inflammation-causing fecal microbes such as Salmonella, E. coli, and Campylobacter. The small intestine has a thinner, less viscous, single-layer mucus barrier, as it is designed for permeability, as this is where the majority of absorption of nutrients—amino acids, fatty acids, vitamins, minerals, etc.—takes place. Fecal microbes should be minimal in the small intestine. The small intestine is permeable, allowing bacterial endotoxin and other factors measuring 2 micrometers or less in width to enter the bloodstream, the size of many microbes.

Witness what happens when you consume something contaminated by E. coli or Salmonella, i.e., food poisoning from the teenager who prepared your fast food meal after moving his bowels without washing his hands, causing fecal contamination of your food. You promptly develop diarrhea and vomiting, i.e., food poisoning, because fecal microbes do not belong in the upper GI tract. Of course, we now have 100+ million Americans who, due to factors such as antibiotics, have lost beneficial microbes that allowed fecal microbes to ascend up from the colon to infest the 24-feet of small intestine: small intestinal bacterial overgrowth, SIBO, essentially mimicking a low-grade form of food poisoning. The small intestine is ill-equipped to deal with the invasion of fecal microbial species, a phenomenon that erodes the intestinal mucus barrier, allows direct contact with the intestinal wall, and increases entry of bacterial endotoxin into the bloodstream, “endotoxemia.” Microbes themselves can also enter the bloodstream, a processed called “translocation” that can explain how various disease processes and infections can occur. This, of course, is the process that explains how GI microbes, especially those in the permeable small intestine, can be experienced in other parts of the body as cognitive decline and dementia, rosacea or psoriasis, fibromyalgia, higher blood sugar, accumulation of abdominal fat, fatty liver, endometriosis, etc., i.e., all the diseases that are common in modern people.

The microbial composition within the GI tract also influences mucus production and degradation. Faecalibacterium and Akkermansia, for example, support mucus production. Overgrowth, however, of otherwise beneficial species, such as Akkermansia muciniphila (muciniphila = mucus-lover), causes breakdown of mucus that, in turn, yields monosaccharides that cause a bloom in Proteobacteria fecal microbes and Clostridium difficile, microbes with significant pathogenic potential. This, by the way, is the likely explanation for the long-term health complications of diets that do not include microbiota-accessible carbohydrates such as prebiotic fibers, as occurs in many who follow ketogenic or carnivorous diets.

In Part II of this series, let’s discuss the steps you can take to preserve the integrity of your mucus barrier: things to avoid, strategies to improve the mucus barrier.