The human microbiome consists of trillions of bacterial cells that live and flourish throughout the body in places such as the skin, lungs, mouth, and urogenital and digestive tracts. Depending on their location in the body, these beneficial bacterial cells have different characteristics and roles in maintaining health.
The gut is home to over 1 000 different species of microbes, with an estimated 100 million to one trillion cells per milliliter, located in the large intestine alone. These microbes contain at least 100 times more genes than are found in the human genome. It has long been known that the bacteria and microbes in the gut are involved in several important functions including:
- Participating in the synthesis of vitamins B12 and K, folate, and biotin
- Enhancing the immune system
- Providing a physical barrier to harmful pathogens
- Producing short-chain fatty acids that provide energy for colonic cells through fermentation of nondigestible carbohydrates
Unlike the human genome, which is determined at conception, the gut microbiome coevolves with the individual over time and appears to be dependent on a multitude of factors, including: age, long-term dietary habits, lifestyle, environmental exposures, and stress.
Dysbiosis, or disruption of the healthy microbiota, is thought to be a trigger for many diseases. This can be caused by antibiotic use or it may also be a result of stress, or result of the quality and composition of one’s diet. Studies have found that those who eat typical Western diets, high in fat and protein from animal products, and low in plant foods, have less diversity in their gastrointestinal bacteria. Higher fiber diets, and especially those which contain a wide variety of plant foods, appear to promote a greater variety and numbers of healthy bacteria.
There is evidence of an association between the gut microbiome and the following diseases:
- Irritable bowel syndrome: A lack of bacterial diversity may facilitate adhesion of pathogens to the bowel wall.
- Inflammatory bowel disease (Crohn’s, ulcerative colitis): While IBD has a strong genetic component, studies have also identified an over abundance of certain types of bacteria, which causes chronic inflammation and ulceration of the colon lining.
- Colorectal cancer: Cancerous changes in the colon may be due to chronic inflammation caused by dysbiosis, and in turn, the cancerous tissue appears more likely to harbor an overabundance of Fusobacterium, a pathogenic bacterium.
- Obesity: Obese individuals appear to have differences in the gut microbiome as compared to lean individuals. Consuming excess calories over and above what is needed for weight maintenance can alter the gut microbiota, regardless of the quality of the diet.
- Allergy: Certain allergic diseases such as atopic eczema, asthma, rhinitis, and some food allergies may be linked to dysbiosis, especially in infants. In many cases, those affected have less bacterial diversity, possibly due to the “hygiene hypothesis”—a high level of hygiene during the neonatal period that likely reduces exposure to microbes.
- Diabetes and insulin resistance: As in the case of obesity, individuals with diabetes appear to have similarities in their gut microbiome.
Although research on the association between disease and the gut microbiome is still emerging, there appears to be significant evidence that diet plays an important role in developing and maintaining a healthy gut microbiome, which in turn may promote wellness, and/or help to manage numerous diseases.
Consume a high fiber, plant-based diet that includes a variety of fiber sources, to increase the diversity of the gut microbiome.
Limit excess energy consumption, regardless of the composition of the diet.
Consume probiotic rich foods such as kefir, yogurt, and fermented vegetables, with live and active cultures.
Be aware that probiotic supplements may contain varying strains of bacteria, which may target different disorders.
Look for ways to reduce stress, especially if it results in unhealthy eating habits, and/or constipation or diarrhea.