Soluble Fiber: Food for Gut Flora

The human body only produces enzymes to digest proteins, fats, starch and a few simple sugars. The remaining components of food either pass through the intestines undigested (insoluble fiber) or are digested by bacteria and fungi in the colon (soluble fiber.) Soluble fiber feeds gut flora. Insoluble fiber is usually minimized by traditional food preparation, for example grains, because it contains unhealthy materials, such as phytic acid. Soluble fiber is healthy and required for normal development of the gut/immune system, whereas insoluble fiber should be avoided.

Soluble Fibers in Vegetables are Carbohydrates/Polysaccharides

Plant cells are surrounded by cell walls composed of long chains of sugars, polysaccharides. These wall polysaccharides, e.g. pectin, arabinogalactans, xyloglucans, and storage glucans and fructans, are highly complex in structure and can only be digested down to simple sugars by the action of dozens of different enzymes produced by dozens of different bacterial species in the colon. Many plants (as well as fungi and bacteria) also produce unique polysaccharides that are only susceptible to additional unique bacteria enzymes. Thus, digestion of diverse vegetables requires hundreds of different species of bacteria in the gut. Healthy gut flora consists of more than 150 different species of bacteria, which were eaten with food and adapt to the gut environment.

Food Intolerances/Most Food "Allergies"/Constipation Reveal Missing Enzymes

Enzymatic treatment of complex polysaccharides in the gut is a complex process that also yields many intermediate products that can influence both gut flora and the gut itself. A well adapted gut flora can systematically digest most of the food molecules that pass into the colon and produce only short chain fatty acids (CFAs) that feed the colon and pass through the liver to the rest of the body.

Antibiotics or a history of limited food choices and excessive hygiene can result in a simplified gut flora that only partially digests soluble fiber and results in accumulation of unusual byproducts that irritate the gut, and cause bloating and gas. Adverse reactions are called food intolerances or food allergies. Since bowel stools are composed predominantly of loosely packed gut flora, inability to fully digest and convert soluble fiber into more gut flora, also results in constipation.

Soluble Fiber in Meat is also Polysaccharide

Meat is made of fibers of protein connected to bone by polysaccharides. The tendons, gristle and other chewy parts of meat are made of chondroitin sulfate and other glycosaminoglycans (GAGs). Heparin is another GAG, which is released onto the surface of the intestines to block the adhesion of viruses and pathogens to the gut, and is subsequently digested by colon bacteria. Other components of meat (and vegetables), such as nucleic acids and some fats are also digested by enzymes of the gut flora. The versatility of gut flora to adapt to a huge variety of foods permits people to live on very diverse diets, ranging from vegan to paleo.

Modern Diets Starve and Simplify Gut Flora

Modern diets consist of processed foods that are made of fat, protein and starch, all of which are digested and absorbed before reaching the colon. These simplified foods produce a simplified gut flora that may also produce more CFAs rather than stool forming gut bacteria. In other words, eating larger amounts of simpler foods can result in more of the nutrients being absorbed and making it easier to gain weight on less food with a tendency toward constipation. These diets may also select for bacteria that maintain the simplified, "efficient" gut flora community and provide the potential for the spread of obesity through a population. Having friends and relatives who are obese and presumably have gut bacteria that favor obesity, increases the risk of obesity. It seems likely that obesity is contagious.

Simplified Gut Flora also Means a Compromised Immune System

Complexity in the gut flora is also needed to produce a healthy immune system, because different species of bacteria in the gut stimulate the development of different parts of the immune system, which develop in the lining of the gut. Soluble fiber is the normal food for the colon bacteria that control the part of the immune system that regulates autoimmunity and allergy, for example. Obesity is also associated with increased risk of degenerative and autoimmune diseases, which is consistent with defects in the gut flora that reside in the colon. Thus, the modern high carb diet contributes to the symptoms of obesity by elevating blood sugar, blood CFAs, as well as compromising the gut flora needed for normal functioning of the immune system.

Healthy Gut Flora = Anti-Inflammatory Diet + Eating New Bacteria

A damaged or simplified gut flora can be fixed by eating foods that supply nutrients for the body as well as feeding the gut flora, e.g. plenty of different types of soluble fiber. It is also necessary to eat the missing bacteria. Just adding a few probiotics with yogurt will not fix the problem and cooking kills all of the good bacteria. Fermented foods, especially those based on bacteria from your own home and garden, are good sources of health-providing bacteria. Raw vegetables will also provide bacteria that may be useful in your gut flora, as long as the vegetables are not too thoroughly washed. Sterilizing and cooking vegetables may avoid rare pathogens, but will certainly prevent contributions to a healthy gut flora.