Health in Diagrams I — Gut Flora and Diet

---All 200 posts here---

This is the first of three posts to summarize my thoughts on diet, inflammation and disease mediated by gut flora.  I decided that I needed to make my points as explicit as possible by putting them down in diagrams and making references to my other posts.  By the time I finish, I will reach my 200th blog post at Cooling Inflammation.

Health in Diagrams II -- Curing Autoimmunity and Allergies

Health in Diagrams III -- Inflammation from Cell to Tissue

Everyone Leaves Out Gut Flora

I want to first explain and diagram my current understanding of the relationship between gut flora (the complex community of hundreds of different types of bacteria and fungi in the intestines) and diet.  My impression is that many people have health problems based on diet, but when they try to heal their health, they fix their diet and see only limited benefits.  Medicine provides only a temporary treatment using dairy probiotics.  The problem is that they failed to fix their gut flora, which was also damaged by their unhealthy diet.  

Health Requires a Match between Diet and Gut Flora

It is a myth that gut flora will just adjust to diet and a healthy diet leads to a healthy gut flora.  

A damaged gut flora lacks necessary species of bacteria.  Antibiotics, for example, can permanently delete dozens of particular bacterial species of gut flora that can only be replaced by reintroducing the missing bacteria by eating those bacteria again.  The missing bacteria may be needed to digest particular foods and the result is food intolerances, commonly mistaken for food allergies.  Antibiotic use frequently leads to autoimmune diseases, that are caused by deficient regulatory T cells of the immune system that develop in the lining of the intestines in response to particular gut bacteria.  The natural source of gut bacteria is eating the bacteria clinging to raw or fermented vegetables.

Antibiotics and Autoimmunity

Diagram Showing the Interaction of Food, Gut Flora and the Immune System

Food is just Protein, Fat and Soluble Fiber

The human body produces enzymes to fully digest proteins, fats and one polysaccharide, starch.  All other parts of plants and animals are edible (fermented by gut flora) soluble fiber polysaccharides or insoluble, undigestible fiber consisting of cellulose or lignin, which together also make up the undigested organic matter, humus, of soil.  Grains are problematical for health, because their starch is readily converted to sugar, i.e. high glycemic, and their fiber is insoluble (not fermented by gut flora) and high in phytate.  Phytochemicals, plant polyphenolics, are of questionable value as antioxidants and are of unexplored importance for their antimicrobial impact on gut flora.

Phytochemicals, Natural Antibiotics and Antioxidants

Polymers (Protein, Starch) are Hydrolyzed by Enzymes to Oligomers and then Monomers (Amino Acids, Glucose)

The stomach mixes protein digesting enzymes, proteases, and starch digesting amylase, with food protein and starch.  Proteases convert the long chains polypeptides, polymers of protein amino acids, into shorter fragments, oligopeptides.  The specific nature of the stomach proteases leaves groups of basic amino acids (lysine, arginine), heparin-binding domains, intact.  These peptides, similar to the defensins of the microvilli crypts, are anti-microbial and work with residual acidity to reduce bacterial growth in the first part of the small intestines.  Pancreatic enzymes then digest the peptides further and the small peptides are ultimately digested by enzymes on the surface of intestinal epithelial cells just prior to absorption.  Similarly, starch is degraded to oligosaccharide amylodextrins, which are then hydrolyzed to glucose at the intestinal surface prior to absorption.  Amino acids and glucose are not normally available to bacteria in the intestines.

Antimicrobial Heparin-binding Domains

Fats are Dissolved by Bile, Digested by Lipase and Absorbed

Fats are triglycerides, i.e. three fatty acids attached to the three hydroxyl groups of glycerol.  Fats are hard to digest, because they form oily droplets.  The droplets are dissolved in the intestines with bile, which is an acidic form of cholesterol, that is produced in the liver and stored in the gall bladder.  Fat in a meal triggers bile release from the gall bladder into the small intestines.  The bile represents a huge reservoir of the cholesterol that is synthesized by the body and dwarfs the cholesterol content of any meal.  Statins decrease body production of cholesterol, interfere with bile/fat digestion and lower lipid cholesterol levels.  (Unfortunately, lowering lipid cholesterol levels has minimal impact on heart disease and the only impact of statins on cardiovascular disease is through weak anti-inflammatory side effects.)  Pancreatic lipase removes two of the fatty acids from each triglyceride.  The fatty acids (a.k.a. soap) and monoglyceride are absorbed by the intestinal cells and reformed into triglycerides that make their way to lymphatic lacteals and are dumped into the blood, where they circulate as chylomicrons surrounded in lipoprotein.  Lipoprotein lipase binds to heparan sulfate on the surface of blood vessels and gradually removes fatty acids, until the diminished chylomicron is absorbed by the liver and exits as a VLDL.  (Note that this is another connection between lipid metabolism and inflammation, since inflammation decreases heparan sulfate on cell surfaces.  Heparan sulfate also mediates LDL binding to cells and amyloid stacking.)

Heparin-binding Domains

Plant Polysaccharides are Soluble Fiber and Food for Gut Flora

All that remains of food after the protein, fat and glycemic starch (glycogen) have been removed in the small intestines are plant cell wall polysaccharides, resistant starch, storage polysaccharides, e.g. inulin, plant beta-glucan, animal glycans, e.g. chondroitin sulfate and heparan sulfate, and insoluble fiber.  The insoluble fiber passes on to be a minor contributor to the bulk of stools and the rest of the polysaccharide is potentially fermentable by gut flora into short chain fatty acids (formic, acetic, propionic, butyric acids).  Some of the polysaccharides are simple repeating units of one or two sugars in long chains, but others are made of five to ten different sugars in complex branched structures.  Simple repeating polysaccharides require just a few different enzymes for their initial synthesis and a few for their digestion.  Thus, resistant starch can be digested by a couple of enzymes into glucose that can be used by most gut flora.  Arabinogalactan, on the other hand, requires a dozen enzymes for plant synthesis and an equal number of hydrolytic enzymes to produce arabinose and galactose, which require further enzymes for metabolism in a select few of species of gut flora bacteria.  

Resistant Starch as a Panacea

Food Intolerance/“Allergy” Indicates Missing Bacteria

Gut flora in general can produce several hundred different enzymes for digestion of diverse soluble fiber,  but most soluble fiber polysaccharides can only be digested by certain bacteria and those bacteria increase, if the complementary fiber is present in the diet.  If a fiber is absent from the diet, bacteria that specialize in digesting that polysaccharide will be eliminated.  People living on diets limited to just a few types of soluble fiber can only digest those fibers and a shift in diet to other types of soluble fiber will lead to symptoms of dietary upset, such as bloating, gas production and food intolerance.  Food intolerances reflect inadequate diversity in gut flora and a mismatch between bacteria and food.  Food intolerances can be eliminated by repairing gut flora and the typical repair solution is eating homegrown fermented vegetables that provide the missing species of bacteria.

Paleo Gut Flora Repair

Immune Cells Develop in Response to Gut Bacteria

Most of the body’s immune cells are in the intestines.  Cells of the immune system are constantly dividing in bones and the thymus gland, developing in the lining of the intestines and migrating to other tissues.  Filamentous bacteria of the gut flora stimulate the development of aggressive immune cells that kill other cells that are infected with pathogens or viruses or are cancerous.  Furrows perpendicular to the flow of food cultivate the growth of Clostridium species that ferment soluble fiber, e.g. resistant starch, and release butyric acid that stimulates the development of regulatory T cells, Tregs.  It is the Tregs that control the aggressive immune cells and prevent attack on self (autoimmunity) or innocuous antigens (allergy).  It appears that merely eating resistant starch, e.g. potato starch, with probiotics that contain butyric acid producing Clostridium bacteria may provide a cure for many autoimmune diseases.

Free the Animal: A Resistant Starch Primer for Newbies

Gut Biofilms Release Vitamins as Quorum Sensing Signals

 The gut flora lines the intestines in numerous biofilm communities, which form from dozens of different species of bacteria that communicate by exchanging molecules called quorum sensing signals.  These signals from the biofilms intimately attached to the lining of the intestines are vitamins.  Thus, healthy gut flora are the major source of vitamins and other sources, such as fruits and vegetables are only needed, if the gut flora is damaged, e.g. by antibiotics.

Dr. Oz, Vitamins, Biofilms

Volume of Stools Reflects Gut Flora Fermenting Soluble Fiber

The bulk of bowel movements, stools, is bacteria, the compressed gut flora that accumulated in the colon while fermenting soluble fiber.  We always hear that we need to eat fiber for regularity, but since insoluble fiber is only a minor contributor to stool volume and it is associated with anti-nutritive attributes, such as the binding and removal of zinc and iron by phytate, the fiber that counts for regularity is soluble fiber.  Regularity results from the fermentation of soluble fiber polysaccharides producing short chain fatty acids, such as butyrate, that are the major source of energy for colon cells.  And the growing bacteria in the colon provide most of the bulk of the hydrated stools.  Inadequate dietary soluble fiber or damaged gut flora, dysbiosis, leave only dehydrated insoluble fiber and compact stools of constipation.  Constipation can result from dehydration or excessive retention, but chronic constipation, even in the presence of adequate dietary soluble fiber, is an indication of damaged gut flora and an increased risk for diseases resulting from deficiencies of Treg production:  autoimmune diseases and allergies.  Constipation and associated autoimmune diseases can be cured by repairing gut flora and supplying adequate dietary soluble fiber.

Milk, Kefir and Gut Flora

Vitamin C, Guinea Pigs, Limeys and Gut Worms

Scurvy and the Need for Vitamin C

Old timey sailors got the symptoms of scurvy, defective collagen and connective tissue, presumably because they stopped eating leafy greens that contained the needed vitamin C, aka ascorbic acid.  Primates/humans and guinea pigs are among the few animals that lack the ability to make their own ascorbic acid and therefore must eat a diet with a minimum amount of the vitamin to avoid a deficiency disease.  This is the conventional wisdom partially based on observation and experiment, but also founded on conjecture.

Parasitic Gut Worms Were the Natural Source of Vitamin C

I don't believe that vitamins are essential ingredients of a healthy diet, but rather I contend that all of the necessary nutritional chemicals are produced by the microorganisms of the gut.  I have previously discussed the gut flora (bacteria and fungi) as the source of most vitamins.  I wish to expand vitamin production to include gut fauna (animals).  I think that it is likely that intestinal worms are the historically natural source of human vitamin C.

Gut Bacteria Control the Development of the Immune System

The human gut actively communicates with the biofilms of bacteria and fungi that form a lining for the healthy gut.  The aggressive cells of the immune system that attack invading pathogens, develop in response to chemical signals from filamentous gut bacteria, and the suppressive cells of the other half of the immune system, which prevents attack on innocuous food antigens (to avoid allergies) or the human body itself (autoimmunity), develop in response to Clostridium ssp.  Thus, the immune system can be highly compromised, if the gut flora bacteria are damaged, e.g. by antibiotics.

Vitamins are Signaling Chemicals of Gut Biofilms

The communities of bacteria in gut biofilms are self-regulating by exchanging chemicals called quorum sensing signaling molecules.  Different species of bacteria and fungi in the biofilms produce and detect different chemical signals.  Since the biofilms are in intimate contact with the cells that line the gut and absorb dietary nutrients, it is not surprising that the biofilm signaling molecules are also absorbed by intestine cells.  Many of these biofilm signal molecules are vitamins, e.g. the B vitamins.  Gut bacteria are the natural source of most vitamins and healthy gut flora eliminates the need for eating vitamins in food or supplements.  Vitamin deficiencies are a symptom of a damaged gut flora.  Antibiotics and vitamin supplements can damage healthy gut biofilms.

Dietary Soluble Fiber Feeds Gut Flora

The human gut flora consists of a couple of hundred different species of bacteria in each person.  Those bacteria in aggregate can produce about a hundred thousand different proteins that focus on the digestion of food molecules that the upper gut cannot digest and absorb.  Since the upper gut can only digest proteins, fats and starch/sugars, that means that the gut flora eat the rest, undigested plant/animal polysaccharides.  Soluble fiber is the plant polysaccharides, e.g. inulin and pectin, that are digested and feed the gut flora.  The undigested polysaccharides include cellulose.  Lignin and some other plant polymers also pass through the gut and are eliminated.  The undigested stuff is called insoluble fiber and it also has bound phytate, which drags some metals such as zinc out with it.  That is why insoluble fiber, such as wheat bran, is not nutritious or healthy.  Insoluble fiber is also a minor contributor to the bulk of stools, which are made up predominately of the gut bacteria that have grown on soluble fiber.

Sea Voyages Damage Gut Organisms

The hundred of different species of bacteria in the gut change in proportions to adapt to different foods in each meal.  If the diet is fairly constant, then the diversity of the population gradually increases, just as the diversity of species in a tropical rain forest is greater than in a temperate forest.  This also explains why gut flora diversity is far less in the USA than in other parts of the world.  Americans are encouraged to eat diverse diets in the search for vitamins and superfoods.  Each dramatic change in diet makes it hard for the gut flora to adapt and the remaining bacteria are those that are generalists.  It might also be expected that early sailors who changed their diets dramatically when they went to sea, ended up with a highly compromised ship-board gut flora (and fauna.)

The Perils of Hygiene

I have a fascination for stories involving the potential of rampaging tigers.  Images of a tiger attempting to drag a hunter from his seat on an elephant or the need of a colleague to employ an armed bodyguard when capturing crabs from Malaysian Mangrove roots at night, linger in my imagination.  I still think about the report of Wallace guarding his derrière while collecting beetles in Bukit Timah, Singapore, in “The Malay Archipelago.”  Humans tend to be incompatible with lions and tigers and bears, and we wipe them out.  We do the same with bacteria, fungi and worms.  We wash our hands, flush the toilet, use hand sanitizers, kill weeds, spray pesticides, grow meticulous lawns/crops, dose ourselves with antibiotics and cleanse.  We are free of the threat of tigers, but we failed to see what else was lost during their extermination.

Probiotics Don’t Fix the Damage of Antibiotics

Antibiotics ravage gut flora.  It is no surprise that a course of antibiotics frequently leads to diarrhea or constipation, since normal stools require normal gut flora.  What is surprising is that physicians, e.g. Dr. Oz, seem to think that antibiotic decimated gut flora can be fixed with probiotics.  Sure, probiotics can provide a temporary bandaid, since Lactobacilli that would normally live on milk in the gut of newborns, are able to provide most of the functions of an adult gut flora.  But probiotics don’t survive in the adult gut and probiotics to not repair damaged gut flora.

Changes to Gut Flora are Permanent, Unless....

Gut bacteria are like wolves in Idaho.  If you don’t bring in new wolves and stop hunting them, you never again have wolves in the wilderness.  If you don’t bring in new bacteria and feed them, damaged gut flora does not repair.  Antibiotic treatment that wipes out the bacteria needed for development of the suppressive immune system will lead to autoimmune disease.  However, repairing the gut flora by flushing in new bacteria (fecal transplant) or gradually reintroducing new diverse bacteria with fermented foods, can also reverse autoimmune diseases as the immune system is repaired.

Parasitic Worms Were Lost at Sea

We think that vitamin C is only provided by plants that we eat, because we didn’t notice what was lost when we cleaned out the worms that typically inhabit the human gut.  Who would have thought that those inconvenient creatures were there for our own good?  We unknowingly compensated for the lost vitamin C production of the worms by incorporating foods rich in vitamin C in our diets.  Shipboard diets that eliminated bowel worms were augmented with limes rich in ascorbic acid.

Guinea Pigs Also Need Worms

It is interesting to note that the experimental animal used to replicate human nutritional requirements for vitamin C is the guinea pig, which is one of the few animals (in addition to bats and primates) that doesn’t make its own.  It is also interesting that guinea pigs (and bats?) commonly have intestinal worms that have to be purged from their bowels before they are used in the lab. 

Gut Flora and Fauna Provide Vitamins

My bottom line is that a normal, healthy gut contains all of the bacteria, fungi and worms to supply all of the needed vitamins.  I do, however, think that dietary vitamin C is a good replacement for one function of intestinal worms, even though I will be watching for other benefits ( Helminth therapy?) that were lost with the removal of these parasites.

Some points:

•   Many vitamins are signal molecules for gut biofilm quorum sensing.
•   Intestinal worms are the typical source for human vitamin C.
•   Vitamin D is a hormone produced in the skin in response to sunlight.
•   Vitamin supplements are unnecessary (problem?), if gut flora and fauna are healthy.
•   Modern diets and hygiene eliminate gut parasites, so food needs to supply vitamin C.
•   Chronic inflammation consumes vitamin C and eliminates production of vitamin D.

New Antibiotics, Biofilm Inhibitors, Vitamin Deficiency

I was not expecting my recent reading of an article on femtosecond reaction kinetics to produce another discussion of quorum sensing, biofilms and vitamins. The idea behind the article was to identify new targets for drug design based on the ephemeral transition states that occur as enzymes bind substrates, stabilize transition states and yield product molecules. Drugs that mimic the transition states make good enzyme inhibitors. One of the target enzymes for the control of disease is an enzyme, MTAN, involved in the synthesis of quorum sensing molecules that orchestrate the construction of common biofilms. The idea is to inhibit MTAN and also avoid selection for antibiotic resistance. Unfortunately, targeting quorum sensing molecules also may produce vitamin deficiencies, since many of these molecules, in this case vitamin K, are also quorum sensing molecules.

Drugs have too many Side Effects
Specificity in the binding of molecules to the thousands of proteins that are coded by the ca. 20,000 human genes depends on a very tight fit between the molecular "key" and the binding site "lock" of the protein. Just as in physical world, a small key/drug molecule with limited surface detail is not as safe/specific as a larger key with many surface features, and a larger lock/enzyme active site that is harder to pick/has fewer interactions with random enzymes. Unfortunately, most drugs are small molecules with limited surface features that make them like molecular skeleton keys that produce many side effects by interacting with unintended proteins/enzymes.

Transition States are more Specific
A recent focus on drug research is to exploit molecular computation and modeling to design molecules that will bind to the part of an enzyme that actually participates in binding substrates and catalyzing chemical reactions. These designed molecules can interact with an expanded region of the enzyme and bind more strongly than the normal substrate. The designed molecules can be very effective inhibitors that will not react as nonspecifically as inhibitors identified by trial an error, e.g. statins.

Biofilm Inhibitors are Targets for Antibiotic Development
The enzymes involved in the synthetic pathways of biofilm quorum sensing signals have been identified and powerful inhibitors of some of these enzymes have now been designed and synthesized. These inhibitors are very effective in inhibiting biofilm formation by some common bacterial pathogens (and essential gut flora.)

Biofilm Inhibitors will also Block Vitamin Production in Gut Biofilms
The new biofilm inhibitor antibiotics may have enhanced specificity, but they target enzymes that also provide essential functions in biofilms that are needed for healthy gut and immune system function. Many of the vitamins that are produced by gut flora are also quorum sensing signal molecules in healthy gut biofilms. Thus, blocking MTAN to block biofilm formation of a pathogen, will also block gut synthesis of vitamin K, which is made in gut bacteria using the MTAN pathway. These inhibitors would be expected to be particularly damaging to the specialized gut flora of breastfed babies, since these gut bacteria are known producers of vitamin K.

Biofilms as Human Gut Mycorrhizals

Are Biofilms Healthy Extensions of Intestinal Villi?

If soil is the stomach of the earth, then plant roots and mycorrizal fungi must be the intestines.

Mycorrhizal fungal hyphae extend from root hairs of plants into surrounding soil and enhance the uptake of phosphate and other nutritents.  Many plants cannot colonize new soil without taking their fungal partners with them.  It would seem obvious that the highly adapted human gut flora would include bacteria and fungi that actively communicate with intestinal epithelial cells.  Perhaps that communication includes both nutrients, e.g. hydrogen, ammonia, etc., vitamins and bacterial wall components, e.g. LPS.

Plants Sit and Mine Soil, Humans Mine Nutrients Passed through Their Gut

I want to try to give a plant’s view of human digestion.  Plants elaborate roots that branch repeatedly and the final extensions sprout hairs from individual epithelial cells.  Mycorrhizal fungal hyphae further extend the reach of the plant into the soil for nutrients. 

I think that a plant would look at us and see us stuffing soil/food into our mouths and watch it come out the other end.  It would then try to figure out where are roots are, i.e. how we absorb the water and minerals from our moving internal stream of soil.  The villi of the small intestines would look like root hairs, but where are the mycorrhizal fungi?  Another problem is that the soil keeps moving past the root hairs and would break off fungal hyphae extending into the soil.  Still another problem is the constant shedding of epithelial cells from the tips of the villi.  The plant would be perplexed, but closer inspection would reveal that biofilms could solve the problems.

Biofilms Coat the Intestinal Villi

Biofilms coating and perhaps spanning the villi of the small intestines may enhance the transport of nutrients into the villi.  This may be controversial and the biofilms may be more commonly limited to the smoother surface of the colon.  The point here is that biofilms may enhance the intestinal uptake of nutrients from food.  Biofilms may, therefore, be essential for health and extend the reach of the intestinal epithelial cells.

Bacterial Community Composition May Be Determined by Diet

A biofilm is composed of some type of linear polymer, such as DNA, heparan sulfate or bacterial acidic polysaccharides, with bacteria that bind to the polymer and to the intestinal epithelium.  Diet determines the bacterial composition of the biofilm.  Thus, the newborn starts without biofilms, gut development is finished by growth hormones in milk and a single species of Bifidobacteria excludes biofilm production, until solid food or formula initiates adult biofilms.  The bacteria in the biofilm depend on diet, so the biofilms can be either beneficial or pathogenic.

Communication within Biofilms and with the Intestines

The bacteria respond to the presence of other bacteria by quorum sensing, which involves release of small molecules that alter the gene expression of other bacteria in the community.  As a consequence, genes, e.g. antibiotic resistance, are exchanged and metabolism is altered.  This is how Klebsiella nitrogenase and hydrogen production is controlled.  The biofilm bacteria also produce compounds, e.g. vitamin D (?), that alter the behavior of the intestinal epithelial cells.  The intestines can respond with inflammation to recognized pathogen components or by triggering development of cells of the immune system.  The intestines are the home of most of the body’s immune cells.

Stimulation of Tregs

Helicobacter pylori adhering to the stomach lining increases the stomach’s quota of regulatory T cells that are involved in immunological tolerance.  Presumably, the supply of Tregs in the intestines is also regulated by biofilms.  Disruption of this system by chronic inflammation can deplete Tregs and lead to unrestrained immune attack that is observed as inflammatory bowel disease.  Thus, Crohn’s disease and ulcerative colitis may be triggered by damaged biofilms.