The Vicious Cycle
The intestinal tract forms a rich ecosystem, comprised of over 400 bacterial species. Some are harmless, and others not. In the gut of a healthy person, these various communities of microbes compete with each other for scarce nutritional resources. Consequently, they exist in a state of balance, and the stomach and small intestine harbour only a sparse population of microbial flora. In the large intestine, each type inhibits an overabundance of the others, and this prevents the waste products and toxins of a particular type of microbe from overwhelming the body. The stomach and upper intestine are also protected by high acidity, and the action of peristalsis.
When the balance in the gut is disturbed, an overgrowth of intestinal flora can result. Microbes migrate to the small intestine and stomach, inhibiting digestion and competing for nutrients. The gut then becomes overloaded with the byproducts of their digestion. This bacterial overgrowth can be triggered by overuse of antacids, reduced stomach acidity due to aging, weakening of the immune system through malnutrition or poor diet, and alteration of the microbial environment through antibiotic therapy.
The components of our diet, particularly carbohydrates, play an enormous role in influencing the type and number of our intestinal flora. When carbohydrates are not fully digested and absorbed, they remain in our gut, and become nutrition for the microbes we host. The microbes themselves must digest these unused carbohydrates, and they do this through the process of fermentation. The waste products of fermentation are gases, such as methane, carbon dioxide & hydrogen, and both lactic & acetic acids, as well as toxins. All serve to irritate and damage the gut. There is evidence that increased acidity in the gut due to malabsorption and fermentation of carbohydrates, may lead common harmless intestinal bacteria to mutate into more harmful ones. Further, lactic acid produced during the fermentation process has been implicated in the abnormal brain function and behavior sometimes associated with intestinal disorders. The overgrowth of bacteria into the small intestine triggers a worsening cycle of gas and acid production, which further inhibits absorption and leads to yet more harmful byproducts of fermentation. The enzymes on the surface of the small intestines are destroyed by the now present bacteria, and this further disrupts the digestion and absorption of carbohydrates, leading to further bacterial overgrowth. As both the microbial flora and their byproducts damage the mucosal layer of the small intestine, it is provoked to produce excessive protective mucus, which further inhibits digestion and absorption.
Damage to the mucosal layer involves injury to the microvilli of our absorptive cells. These microvilli act as the last barrier between the nutrition we take in and our bloodstream. As our absorption is inhibited, folic acid and vitamin B12 deficiency can lead to impaired development of microvilli, while an abnormally thick layer of mucus prevents contact between microvilli enzymes and the carbohydrates we ingest. The small intestine responds to this spiraling irritation by producing more goblet (mucus-making) cells, creating yet more mucus. Finally, as the goblet cells become exhausted, the intestinal surface is laid bare, and is further damaged, and possibly ulcerated. As more carbohydrates are left in the gut, they cause water and nutrients to be pulled from the body into the colon, resulting in chronic diarrhea. Absorption is further hindered as diarrhea increases the rate with which food travels through the gut.
From Breaking the Vicious Cycle website