The bacteria in our lower intestine have evolved over thousands of years to feed on and extract nutrients from the dietary fiber that is not broken down by our primary digestive process. In a sense, they are scavengers but it is perhaps more accurate to say that we are eating to feed two digestive systems – the one that processes proteins, carbohydrates and fats and the one that processes fiber.
If the human micro biome didn’t provide us with solid benefits then it might be OK if we didn’t feed it. However, the reality is that these bacteria are vital to our health and well being. In addition to extracting added nutrition from dietary fiber they constantly monitor the blizzard of bacteria that enter our bodies through our mouths. Those that are friendly and can live in the anaerobic (oxygen free) environment on our large intestine are given a chance to join our diverse gut community while those that are harmful are attacked and eliminated. The micro biome then passes on what it has learned about the invading bacteria to our immune system. In ways that are not yet fully understood the micro biome also produces compounds and enzymes that play a vital role in everything from our appetite and metabolism to our mental health.
When the system works properly, our primary digestive system processes all of the proteins, fats and simple carbohydrates from our last meal and then passes he complex carbohydrates (“indigestible” dietary fiber) on to our lower intestine. This fiber is then set upon by the gut bacteria and subjected to a fermentation process that breaks it down enough to extract most of its remaining nutrients. Because bacteria have their own digestive specialties, both the quantity and type of dietary fiber that we eat will determine both the types and quantity of bacteria that live in our gut. As our gut bacteria break down the dietary fiber they extract the nutrients that they need to live and in the process produce a wide variety of short chain fatty acids and by-product compounds that become the raw material for the protective mucous membrane that lines our gut. The short chain fatty acids pass through the protective wall of the intestine and become nutrients and building blocks for enzymes and proteins that directly impact our physical and mental health.
The evolution of Western diets toward more “refined” foods and away from fiber has left our microboimes undernourished and in extreme cases driven to behavior that is harmful to our overall health just so that they can survive. When they don’t get enough dietary fiber to eat some of the “good” bacteria die out but some of the “bad” bacteria turn to eating the protective mucous membrane that protects the intestinal wall. Depending on how far the breakdown of the mucous membrane progresses, the result can be range from Irritable Bowel Syndrome to Colitis. In the worst case the bacteria begin to penetrate the intestinal wall and mis-lead our immune system into believing that vital body tissues are enemies that need to be destroyed. Recent research has traced a wide range of “auto-immune” problems including Crohn’s disease, Multiple Sclerosis and Uveitis to the disruption or break-down of the micro biome.