Over a hundred trillion bacteria live within us and on us. That's tenfold higher than the number of cells in the human body itself. With a collective weight of 1kg to 1.5kg, this microbiome can be considered an additional human 'organ' of sorts, rivaling the liver in the number of biochemical reactions in which it participates.
This entity contains about four million distinct bacterial genes, 95% or more located in the large intenstine, where they enhance gut motility and function. Colon bacterial species can be divided into potentially harmful or health-promoting groups. "Since most of these genes encode for enzymes and structural proteins that influence the functioning of the mammalian cells," a recent study notes, "the gut microbiome can be viewed as an anaerobic bioreactor programmed to synthesize molecules which direct the mammalian immune system, modify the mammalian epigenome, and regulate host metabolism." (1)
Microbiomes are clusters of mainly bacteria, as well as a few other organisms found in our mouth, skin, nose, urogenitals, ocular tissue and gut. In recent years, scientists have discovered that the gut microbiome orchestrates human metabolism, immunity and gene expression.
The gastrointestinal microbiome modulates the immune system: by shifting T-helper cell balance towards Th1, resulting in decreased production of IgE and eosinophils, dampened hypersensitivity reactions and intestinal inflammation, greater oral tolerance and prevention of atopic diseases. A healthy gastrointestinal (GI) tract improves digestion and nutrient absorption (contributing approximately 10% of daily energy needs), salvages energy from unabsorbed carbohydrates in the colon to form short-chain fatty acids and improves the absorption of calcium, magnesium and trace minerals. A healthy GI tract also produces vitamins in the B and K groups. It also facilitates xenobiotic metabolism, important for the absorption and proper functioning of phytoestrogens, lignans, flavonoids and some medicinal herbs.
Dysbiosis is defined as qualitative and quantitative changes in the intestinal flora, their metabolic activities, or their local distribution that produces harmful effects on the host. Our modern diet and lifestyle, as well as the use of pharmaceutical drugs, has led to the disruption of the normal intestinal microflora and/or its activities. The consequences of our modern lifestyle include an increase in inflammatory disorders such as allergy and autoimmunity, and this is driven by the effect that dysbiotic microbes have on the epigenetic expression of immune system function.
One note of interest involving the role of stress on dysbiosis: when we are under stress, increasing levels of norepinephrine can spillover through simple diffusion into the gastrointestinal lumen where norepinephrine acts as a growth inducer to pathogenic microbes. So, when stressed we are feeding the growth of harmful microbes. Wellness involves more than nutrition and exercise. Stress reduction also plays a key role.
Most importantly, a healthy microbiome provides colonization resistance, or protection against colonization of the intestinal tract with potentially pathogenic bacteria afforded by the intestinal flora. Finally, a healthy micro-flora plays a vital role in weight maintenance and energy homeostasis, preventing obesity by its increased capacity to harvest energy...