Research shows that more than 90% of cells in the human body are microbial, and we are only now starting to discover the complexity of the interaction between the human microbiome (microbes and their genes) and the rest of our body. While outdated textbooks often contain a small segment on gut bacteria and their role in digesting otherwise indigestible carbohydrates, more recent research has made it clear that bacteria affect pretty much the entire human body. It also seems that the microbiome is more important now than in any other part of human evolution since it’s only recently that we systematically damage the human microbiome (and the microbial ecosystems around us) with antibiotics, bottle-feeding and many other factors indigenous to the modern world.
Most of the nutrients we ingest are broken down into smaller parts and absorbed in the small intestine. Carbohydrates you eat are broken down into monosaccharides, proteins into amino acids, and fat into free fatty acids and monoglycerides. However, we don’t have the needed enzymes to break down most complex carbohydrates so we rely on our gut bacteria in the colon to provide the enzymes to properly utilize most of these complex carbohydrates for energy. When we give gut flora access to these types of fermentable substrates, they in turn provide us with short chain fatty acids (SCFA’s) such as acetate, propionatem, and butyrate.
One of the important functions of these SCFA’s is to improve intestinal barrier function, and thereby help prevent a “leaky gut”. Although the term “leaky gut”/increased intestinal permeability has been used by alternative health practitioners for a long time, it’s only recently that scientific studies are beginning to pile up, showing that leaky gut definitely is a real condition. Some experts even go as far as to say that increased intestinal permeability might be the number one cause of low level chronic inflammation in the U.S. and other industrialized countries.
Although a wide spectrum of complex carbohydrates are broken down by different types of gut bacteria, prebiotics are characterized as food ingredients that are especially effective in stimulating the growth and/or activity of bacteria in the digestive system in ways claimed to be beneficial to health. Oligofructose, pectin and resistant starches are well-known prebiotics that increase the growth of beneficial bacteria such as bifidobacteria in the intestine. Prebiotics are often recommended because they seem to promote a healthy composition of bacteria and increased production of SCFA’s.
A lack of complex carbohydrates, with the exception of starch, in the standard american diet is most likely one of the reasons why poor gut flora, increased intestinal permeability, inflammation and disease is so common.
Small intestinal bacterial overgrowth is a disorder of excessive bacterial growth in the small intestine. While the large intestine (colon) is naturally rich in bacteria, bacterial overgrowth of the small intestine may increase degradation of fermentable substrates before they reach the colon.
Protein and fat digestion
Bacteria in the digestive system are mainly found in the large intestine/colon, and since fat and protein are absorbed in the small intestine, it’s primarily carbohydrates that pass on into the large intestine. If proteins are allowed to pass into the colon, colonic protein metabolism via the gut microflora could occur, and the metabolites of this process might increase the risk of certain diseases such as colorectal cancer.
Although gut flora seem to be most important in the digestion of carbohydrates, some studies show that bacteria both in the upper parts of the gastrointestinal tract and in the colon play a role in the digestive process of fat and protein:
– “…gut microflora could potentially play a major role in proteolysis (breakdown of protein) in the human colon.” (1)
– “…bacteria may be exploited for physiologic degradation of harmful gluten peptides.” (2)
– “…different members of the intestinal microbiota promote fatty acid absorption via distinct mechanisms” (3)
Digestive problems as a result of gut dysbiosis
Since gut bacteria play an essential role in the digestion of nutrients and in the development and control of the immune system, there’s no surprise that celiac disease, clostridium difficile infection, food intolerance, gallstones, irritable bowel syndrome, inflammatory bowel disease and most other types of digestive diseases are characterized by gut dysbiosis.