The human body hosts trillions of germs, and these microorganisms and their DNA is collectively called the human microbiome. While most of these microbes are considered beneficial to the human host, others are potentially pathogenic under the right circumstances. The human microbiome consists of microorganisms that live in the mouth, lungs, sinuses, gastrointestinal tract, and several other places in and on the body. We provide these microbes with food and shelter, and they provide us with functions that stretch far beoynd the scope of our own physiological capabilities. However, if we perturb these microbial ecosystems, the relationship between the microbiome and the human host can change from symbiosis to dysbiosis.
Dysbiosis can happen on any exposed surface or mucous membrane
“Dysbiosis (also called dysbacteriosis) refers to a condition with microbial imbalances on or inside the body. Dysbiosis is most prominent in the digestive tract or on the skin, but can also occur on any exposed surface or mucous membrane such as the vagina, lungs, mouth, nose, sinuses, ears, nails, or eyes” (1).
Perhaps the most well-known type of dysbiosis among the general public, is vaginal dysbiosis. Imbalances in the microbial communities in the vagina set the stage for vaginal thrush and other microbial disturbances (2,3).
Dysbiosis in the mouth is also very common and results in tooth decay and poor periodontal health (4).
The majority of microbes live in the gastrointestinal tract, and more specifically in the large intestine where they digest some of the food we eat and regulate our immune system and intestinal barrier function. Gut bacteria are essential to our health and provide several important functions we can’t do without:
- Essential metabolic functions (5,6)
Production of vitamins, amino acid synthesis, digestion of fermentable substrates, production of short-chain fatty acids, and bile acid biotransformation.
- Ensures protection (5,6)
Commensal bacteria prevent pathogenic colonization and regulate the immune system
- Structural and histological functions (5,6)
Bacteria in the gut ensure intestinal structure and function
While the largest colonies of bacteria live in the colon, gut dysbiosis can also affect the upper parts of the gastrointestinal tract.
Hundreds of different types of microorganisms make up the gut microbiota, and various species of bacteria have different functions in the body. Even in a balanced state, a lack of microbial diversity leads to poor digestion and low-level inflammation, since microbes produce enzymes that are needed to digest otherwise undigestible food components.
Since bacteria in the gut have so many important functions in the body, disruptions in this microbial ecosystem are also linked to the most serious health problems. Altered composition of the gut microbiota can lead to serious immune deregulation, increased intestinal permeability, endotoxemia, bacterial infection, abnormal bacterial metabolite levels, altered energy and lipid metabolism, and chronic low-level inflammation (7,8,9). When considering the vital importance of a healthy and balanced microbial ecosystem in the gut, it’s no surprise that gut dysbiosis is linked to a plethora of human disorders such as autoimmune disease, allergic disease, irritable bowel syndrome, metabolic disease, alcoholic liver disease, bacterial infection, and colorectal cancer (7,8,9).
Dysbiosis is extremely common
The obvious disconnect between our evolutionary past and the modern envoronment has led to dramatic changes in the human microbiome. Since the majority of people in the industrialized world use antibiotics some time during their life, eat a typical western diet high in processed and refined food, spend little time outdoors compared to our ancestors, and have limited exposure to soil microbes and other types of bacteria, I believe dysbiosis is now quickly becoming the leading cause of disease in the modern world.