STORY AT-A-GLANCE
Your gut is home to bacteria, viruses, fungi, archaea and eukarya; bacteria make up the vast majority of microbes in your microbiome
While your highly acidic stomach may host only about 1,000 colony-forming units (CFU) of bacteria per milliliter (mL), your large intestine is home to up to 1 trillion CFU/mL
Bacteroides are the dominant microbe in your large intestine; the composition of these microbes, and those elsewhere in your gut, are linked to health conditions like obesity, depression, Alzheimer’s disease and inflammation
Your age, health status, diet and environment all influence the numbers and diversity of microorganisms in your gut
A healthy gut microbiome depends on the consumption of whole, fermented foods and the avoidance of unnecessary antibiotics and other environmental assaults; spore-based probiotics are one option to help
The human gut is finally receiving the respect it deserves — and so are its trillions of inhabitants.1 You are, at your core, a microbial being,2 and while microorganisms are found everywhere from your skin to your mouth and even your blood,3 it's your large intestine where your body's largest bacterial ecosystem resides.4
If you treat it and the rest of your microbiome well, good health — both mental and
physical — is likely to result. By nourishing this complex microbial community, you can
even influence your gut-brain axis, which regulates digestion, mood, immune function and much more.5
The Number of Microbes Living in Your Gut Is Staggering
Your gut is home to bacteria, viruses, fungi, archaea and eukarya. The latter two resemble bacteria but are distinct groups of microorganisms. Bacteria, meanwhile, make up the vast majority of microbes in your microbiome. Three main phyla or groups
of gut microbes make up the human microbiome and serve diverse structural, protective and metabolic functions:6
Bacteroidetes — Porphyromonas, Prevotella and Bacteroides
Firmicutes — Ruminococcus, Clostridium, Lactobacillus and Eubacteria
Actinobacteria — Bifidobacteria (the most prevalent type)
Broken down, the average person may host the following quantities of bacteria in
different body regions.7 Remember that this is just an average — your age, health status, diet and environment all influence the numbers and diversity of microorganisms in your gut.8
Mouth — 100,000 colony-forming units (CFU) per milliliter (mL)
The digestion process begins in your mouth when you chew your food, making it easier to break down in your gut. Your mouth contains an impressive number of microbes to maintain oral health but if they become out of balance, disease may result.
For instance, the bacteria in your mouth are thought to play a role in blood pressure via nitric oxide (NO), a soluble gas stored in the lining of your blood vessels, called the endothelium. However, antiseptic compounds in mouthwash may destroy beneficial oral bacteria that are important for maintaining blood pressure, thereby contributing to high blood pressure levels.
In one study, the use of the mouthwash twice daily was associated with a significant increase in systolic blood pressure after one week, while once the mouthwash was stopped, "recovery from use resulted in an enrichment in nitrate-reducing bacteria on the tongue."9
Differences in more than 10 species of bacteria living on the tongue were noted after mouthwash use, including lower microbial diversity after one week of use.10 As noted in a Frontiers in Bioscience review, nourishing and protecting your oral microbiome may reduce your risk of multiple diseases:11
"Recent studies show that one approach to reducing the risk of chronic
infections, such as caries, gingivitis, periodontitis, and halitosis, is to control the ecology of the oral microbiome instead of completely removing both the
harmful and beneficial microorganisms.
This is based on the knowledge that oral diseases are not caused by a single pathogen but rather by a shift in the homeostasis of the entire microbiota, a process known as dysbiosis."
Pseudomonadota, which are present in higher concentrations in the mouth than in the gut,12 also play an important role in producing short-chain fatty acids and boosting the growth of beneficial gut microbes.13
Fusobacteriota represent another prominent type of microbes in the body. While they can help stimulate inflammatory responses to fight
pathogens, they may also drive inflammation and are linked to periodontal disease.14
Esophagus — 10 Million CFU/mL
Firmicutes tend to be particularly abundant in the esophagus. While relatively low in numbers compared to elsewhere in the gastrointestinal tract, Firmicutes are useful for helping to break down sugars and carbohydrates from the foods you eat.15
Interestingly, Firmicutes, which are centrally involved in glucose and insulin metabolism, belong to the phylum most adversely affected by the artificial sweetener sucralose.16
Animal studies suggest the sucralose-altered gut microbiome could be involved in inflammation of the gut and liver, as well as cancer.17