Body System

Gut Microbiome

Also known as: gut microbiota, intestinal flora, intestinal microbiota, gut flora

The community of bacteria, archaea, fungi, and viruses living in the human digestive tract — 300-1,000 species, dominated by Bacteroidota and Bacillota phyla, contributing roughly 100× more genes than the human genome itself. Ferments dietary fiber into short-chain fatty acids that fuel colon cells, train immunity, and signal the brain. Dysbiosis associates with major chronic diseases including IBD, type 2 diabetes, obesity, depression, and colorectal cancer.

The human gut is not, biologically, a single organism. It is a coordinated ecosystem of one human body and ~38 trillion bacterial cells [1] — a co-evolved community whose interactions are now understood as central to [[immune-system|immunity]], metabolism, neurological function, and resistance to chronic disease.

Composition

The gut hosts a community of bacteria, archaea, fungi, and viruses [2]. The colon contains 300 to 1,000 different species, though “99% of gut bacteria come from about 30 or 40 species” [2]. The community is far less diverse than the available species pool would suggest — most of the daily metabolic work is done by a relatively small set of dominant species.

Dominant bacterial phyla [2]:

Bacteroidota (formerly Bacteroidetes) — Bacteroides alone comprises ~30% of gut bacteria
Bacillota (formerly Firmicutes) — includes Faecalibacterium prausnitzii, a major butyrate producer
Actinomycetota — includes Bifidobacterium, important in infant microbiomes
Pseudomonadota — typically a smaller fraction; overgrowth associated with dysbiosis

Major bacterial genera worth knowing [2]:

Bacteroides — the dominant by mass
Faecalibacterium prausnitzii — anti-inflammatory butyrate producer; often depleted in IBD
Bifidobacterium — important in infants; declines with age and diet
Lactobacillus — major probiotic genus; ferments fiber and lactose
Clostridium — diverse genus; some species beneficial, others pathogenic (C. difficile)
Akkermansia muciniphila — mucin-degrader; associated with metabolic health

Functions

The gut microbiome contributes to host physiology across multiple pathways [2]:

Digestion and metabolism

The microbiome ferments indigestible carbohydrates (fiber, resistant starch) into [[short-chain-fatty-acids|short-chain fatty acids]] — primarily butyrate, propionate, and acetate. These provide:

Butyrate — primary energy source for colonocytes (colon lining cells)
Propionate — supports liver ATP production and gluconeogenesis
Acetate — fuels muscle and brain metabolism

Bacteria also synthesize B vitamins and vitamin K that the host cannot make itself.

Immune development and training

The gut-associated lymphoid tissue (GALT) — the largest collection of immune cells in the body — develops in dialogue with the microbiome. Different bacterial species drive different immune responses:

Some species promote anti-inflammatory cytokines (Treg-supporting)
Others stimulate protective Th17 responses against pathogens
The balance is what produces healthy immune tolerance — neither immune deficiency nor chronic inflammation

Gut-brain axis

The microbiome influences brain function through multiple pathways [2]:

Microbial metabolites circulating in blood reach the brain
Vagus nerve signaling carries information from gut to brain
Neurotransmitter precursors — gut bacteria produce or modulate ~90% of the body’s serotonin, plus GABA, dopamine precursors, and others
Inflammatory signaling — gut inflammation correlates with mood disorders

This is the biochemical basis of the now-substantial literature on gut microbiome contributions to depression, anxiety, autism spectrum conditions, and neurodegenerative disease risk.

Pathogen exclusion

A healthy diverse microbiome occupies ecological niches and produces antimicrobial compounds that prevent pathogen colonization. Disrupting the microbiome (notably via broad-spectrum antibiotics) creates space for opportunistic pathogens — Clostridioides difficile infection is the classic example.

Dysbiosis and disease

Dysbiosis is the umbrella term for disturbed microbiome composition. Documented disease associations [2]:

Inflammatory bowel disease (IBD) — Crohn’s, ulcerative colitis; depleted F. prausnitzii, increased pathobionts
Type 2 diabetes — reduced diversity, altered SCFA profile
Obesity — multiple altered ratios (Firmicutes/Bacteroidetes ratio is the most-cited)
Colorectal cancer — high-fat-diet-driven bile acid shifts promote dysbiotic patterns
Asthma and allergies — early-life microbiome disruption (especially from C-section delivery + antibiotics) associates with increased risk
Depression and anxiety — [[gut-brain-axis|gut-brain axis]] disruption
Autoimmune disease — multiple sclerosis, rheumatoid arthritis, type 1 diabetes; microbiome-immune training mismatches

The disease associations are real but the causal direction is not always clear. Much research is still working out which dysbiotic patterns cause disease vs which result from disease vs which simply correlate.

Practical implications

What modifies the gut microbiome [2]:

Builds it up:

High dietary fiber diversity (multiple plant species per week)
Fermented foods (yogurt, kefir, kimchi, [[sauerkraut|sauerkraut]], miso, [[kombucha|kombucha]], sourdough)
Adequate sleep and stress management
Outdoor time and contact with diverse environmental microbes
Vaginal birth and breastfeeding (early-life seeding)
Selective probiotic supplementation (effects are strain-specific and condition-specific)

Tears it down:

Broad-spectrum antibiotics, especially repeated or in childhood
[[ultra-processed-foods|Ultra-processed foods]] (reduced fiber diversity)
Chronic stress (via cortisol-mediated effects)
Certain medications (proton pump inhibitors, some chemotherapies)
Glyphosate exposure (some evidence; controversial)
C-section birth (reduced early-life seeding) and formula feeding

Restores it after disruption:

Time + diet + sleep
Targeted probiotics (specific strains for specific conditions)
Fecal microbiota transplant (FMT) — 85-90% effective for recurrent C. difficile [1]; experimental for IBD, autism, and other conditions

Diet — fiber as substrate

The single most-evidence-supported intervention for microbiome health is dietary fiber diversity [2]. Without fiber to ferment, beneficial bacteria starve. Low-fiber Western diets correlate with:

Reduced microbial diversity
Reduced SCFA production
Increased dysbiosis-associated disease

The actionable rule (the “Sonnenburg rule” from Stanford research): aim for 30+ different plant species per week. Includes fruits, vegetables, grains, legumes, nuts, seeds, herbs, and spices — each species feeds slightly different bacteria. The diversity is the active ingredient.

This is one of the strongest cases the wiki has for modern science arriving at conclusions that traditional dietary wisdom held intuitively: traditional diets across most cultures historically included far more plant species per week than typical Western industrial diets. The microbiome research is, in part, modern explanation of what was already practical wisdom.

Connection to TCM

The gut microbiome science maps suggestively onto TCM’s framework — see [[traditional-chinese-medicine]]. The TCM concept of Spleen Qi (the digestive-energy organ system) extracting Grain Qi from food has clear functional parallels with microbiome-mediated extraction of nutrients and SCFAs from dietary fiber. Diseases that TCM frames as “Spleen Qi deficiency” (fatigue, loose stools, low appetite, easy bruising, weak [[immune-system|immunity]]) overlap substantially with dysbiosis presentations.

The wiki should not collapse one framework into the other — they emerged from different methods and use different language. But the convergence is suggestive and worth documenting.

Why it matters here

The gut microbiome is one of the wiki’s deepest connection points between food entities and body systems. Every food’s effect on health flows substantially through its effect on the microbiome. Future food entries should declare microbiome-relevant relations:

High-fiber foods → feeds the microbiome
Fermented foods → seeds the microbiome
[[ultra-processed-foods|Ultra-processed foods]] → starves the microbiome
Antibiotic residues in conventional meat → disrupts the microbiome

This page is also the wiki’s first body-system entity — the format example for organ systems, [[immune-system|immune system]], [[nervous-system|nervous system]], cardiovascular system, etc., to follow.

Lenses still to grow

Specific bacterial species in detail — Akkermansia, F. prausnitzii, L. reuteri, etc.
Fermented foods — comprehensive entry for each major tradition
Prebiotic vs probiotic distinction in clinical detail
Fiber types — soluble, insoluble, resistant starch, beta-glucan, inulin
[[gut-brain-axis|Gut-brain axis]] in full peer-reviewed depth — depression, autism, neurodegeneration
Industrialized vs ancestral microbiomes — Hadza, Yanomami research
Pediatric microbiome development — first 1,000 days of life
Energetic / TCM — the Spleen Qi correspondence in clinical practice; how a TCM practitioner would treat dysbiosis presentations
Glyphosate-microbiome controversy — the contested research
Specific dietary protocols — low-FODMAP, autoimmune protocol, the various “gut-healing” approaches and their evidence

Sources

Wikipedia: [[microbiome|Human Microbiome]]. 38 trillion bacterial cells, 30-40 trillion human cells, gene count ratio (~100×), [[microbiome|Human Microbiome]] Project context, 10,000+ species catalogued, 85-90% FMT success rate for C. difficile. https://en.wikipedia.org/wiki/Human_microbiome
Wikipedia: Gut Microbiota. 300-1,000 species, 99% from 30-40 dominant, dominant phyla (Bacteroidota, Bacillota, Actinomycetota, Pseudomonadota), major genera (Bacteroides ~30%, F. prausnitzii, Bifidobacterium, Lactobacillus, Clostridium, Akkermansia), digestive/immune/gut-brain functions, dysbiosis-disease associations (IBD, T2D, obesity, colorectal cancer, asthma), fiber substrate role, prebiotic vs probiotic, antibiotic effects. https://en.wikipedia.org/wiki/Gut_microbiota

Specific clinical research, the Sonnenburg lab work on fiber diversity, [[gut-brain-axis|gut-brain axis]] primary literature, and detailed bacterial-species accounts warrant primary-source citation as this page is enriched.

All sources retrieved 2026-05-02.

What links here, and how

Inbound connections from across the wiki, grouped by lens and by relationship. These appear automatically — every entity page declares what it links to, and that data populates here on the targets.

Scientific

enables

Apple the pectin specifically supports beneficial bacteria; one mechanism for apple's documented health benefits
Death the gut microbiome's principal function is decomposition — the breakdown of complex matter into forms the host can use; the same biological pattern that drives soil decay drives the gut
Energy the gut is an energy-conversion system; the microbiome's role is converting forms of chemical energy the human enzyme system cannot access into forms it can
Microbiome the gut microbiome is the most-studied and clinically important microbiome region

shares substrate with

Bioavailability gut microbiome composition substantially affects bioavailability of many compounds, particularly polyphenols
Endocrine system gut microbiome composition substantially affects endocrine function through bile-acid metabolism, estrogen reactivation (estrobolome), and HPA-axis regulation
Gut-brain axis the microbiome is the principal mediator of gut-brain axis communication
Polyphenols much of dietary polyphenol activity occurs through gut-microbiome metabolism into bioactive metabolites

parallels

Butyrate butyrate is the most-studied product of the gut microbiome's fiber-fermenting work; its production is a direct measure of microbiome function
Distributed Cognition distributed cognition is to the brain as the gut microbiome is to the digestive tract — the recognition that the host is not the entire functional system
Lactic acid many gut microbes produce lactic acid as part of fiber and sugar fermentation; lactic-acid producers are foundational members of healthy gut communities
Mycorrhizal Fungi the soil-fungi-and-plant-root system is structurally analogous to the gut-microbiome-and-intestinal-villi system: an external symbiotic biological partner extending the host's effective absorptive surface area many times over and trading metabolites in both directions

rests on

Cognitive Symbiosis the gut-brain axis is the canonical animal case — the host's cognition is partly shaped by, and partly distributed across, microbial partners

feeds

Dandelion dandelion root is one of the highest-known sources of inulin (a fructan prebiotic) — particularly in autumn-harvested roots; the inulin selectively feeds Bifidobacteria and contributes to short-chain fatty acid production
Garlic raw garlic is a documented prebiotic — fructans (specifically inulin-type fructans) reach the colon undigested and selectively feed Bifidobacteria; cooked garlic loses some but not all of this effect
Kale high in insoluble and soluble fiber plus glucosinolate compounds; the fermentable fraction supports butyrate-producing bacteria and contributes to short-chain fatty acid production in the colon

substrate of

Fermentation fermented foods supply living microbes and microbial metabolites that feed the gut microbiome — one of the diet-microbiome links best-documented
Kefir kefir's exceptional microbial diversity (30+ species) makes it one of the most-studied fermented foods for gut-microbiome impact
Kimchi live kimchi delivers diverse Lactobacillus species; Korean diets high in kimchi have been studied for gut-microbiome diversity outcomes
Kombucha live kombucha contains acetic-acid bacteria, yeasts, and small amounts of probiotic species; gut-microbiome research is ongoing
Sauerkraut live unpasteurized sauerkraut delivers Lactobacillus and other LAB to the gut along with prebiotic fiber
Yogurt live yogurt is one of the most-studied fermented-food sources of probiotic Lactobacillus and Streptococcus species

threatens

Glyphosate the shikimate pathway glyphosate inhibits is present in many bacterial species in the human gut; potential microbiome disruption is documented but contested in scale and clinical relevance

shares approach with

Jerusalem artichoke tubers are rich in inulin, a prebiotic fiber that feeds beneficial gut bacteria

produces

Short-Chain Fatty Acids produced by gut bacteria fermenting dietary fiber and resistant starch

kin of

Sourdough starter Same evolutionary logic — humans and microbes co-fermenting, each providing what the other needs. The starter on the counter and the microbiome in the gut are the same domestic biology, externally and internally.

Medicinal