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# Microbiome

mi·cro·bi·ome - MY-kro-BY-ome

## Definition

The microbiome refers to the vast community of trillions of microorganisms - including bacteria, viruses, fungi, and other microbes - that live in and on your body. While microbiomes exist on the skin, in the mouth, and in other body sites, the term most commonly refers to the gut microbiome: the ecosystem of microorganisms inhabiting your gastrointestinal tract, primarily the large intestine.

Your gut microbiome contains an estimated 38 trillion bacterial cells - roughly equal to the number of human cells in your body - representing hundreds of different species. Far from being passive passengers, these microorganisms play active, essential roles in digestion (breaking down fiber and producing nutrients your body can't make on its own), immune system development and regulation, protection against harmful [pathogens](/glossary/pathogen), and even communication with the brain through the gut-brain axis.

Every person's microbiome is unique, shaped by factors including genetics, birth method (vaginal vs. cesarean), breastfeeding, diet, antibiotic use, environment, stress levels, and age. Research is increasingly revealing that the composition and diversity of your gut microbiome has far-reaching effects on virtually every aspect of health - from metabolic function and [immune responses](/glossary/immune-response) to mental health and disease risk.

## Also Known As

Gut microbiome Gut flora Intestinal microbiota 

## Key Facts

-   • The gut microbiome weighs approximately 2-5 pounds - roughly the same as the human brain. 
-   • Gut bacteria produce essential vitamins including vitamin K, B12, biotin, and folate. 
-   • Approximately 70% of the immune system is located in or around the gut. 
-   • Microbiome diversity - having many different species - is generally associated with better health. 
-   • Diet is the most powerful modifiable factor affecting microbiome composition - changes can be detected within 24 hours of dietary shifts. 
-   • The gut microbiome produces approximately 90% of the body's serotonin, a key neurotransmitter for mood regulation. 

## How It Relates To Your Health

Your gut microbiome influences far more than digestion. Research has linked microbiome disruption (dysbiosis) to conditions including obesity, [type 2 diabetes](/conditions/type-2-diabetes), inflammatory bowel disease, allergies, autoimmune conditions, depression, and anxiety. Understanding the microbiome helps explain why diet has such a profound impact on overall health - when you eat, you're not just feeding yourself; you're feeding trillions of organisms that in turn influence your [metabolism](/glossary/metabolism), immune function, and brain chemistry.

The most effective way to support a healthy microbiome is through dietary diversity: eating a wide variety of plant foods (aim for 30+ different plants per week), consuming prebiotic-rich foods (garlic, onions, leeks, asparagus, oats), including fermented foods (yogurt, kimchi, sauerkraut), and minimizing processed foods and unnecessary antibiotics.

## Related Terms

[Irritable Bowel Syndrome](/glossary/irritable-bowel-syndrome)[Leaky Gut Syndrome](/glossary/leaky-gut-syndrome)[Serotonin](/glossary/serotonin)[Cytokines](/glossary/cytokines)[Inflammation](/glossary/inflammation)

## Related Conditions

[

### Irritable Bowel Syndrome

Digestive 

IBS is a common functional gastrointestinal disorder characterized by recurring abdominal pain, bloating, and changes in bowel habits without any visible damage to the digestive tract. Triggers often include certain foods, stress, and hormonal changes.

Abdominal cramping Bloating and gas Diarrhea or constipation 

Chronic Learn More 

](/conditions/irritable-bowel-syndrome)[

### Crohn's Disease

Digestive 

Crohn's disease is a type of inflammatory bowel disease that causes chronic inflammation anywhere in the digestive tract, most commonly the end of the small intestine. It can penetrate deep into bowel tissue and lead to serious complications including strictures and fistulas.

Persistent diarrhea Abdominal pain and cramping Blood in stool 

Chronic Learn More 

](/conditions/crohns-disease)[

### Celiac Disease

Immune System 

Celiac disease is a genetic autoimmune disorder in which eating gluten - a protein found in wheat, barley, and rye - triggers an immune response that damages the small intestine's lining. This prevents proper nutrient absorption and can lead to a wide range of symptoms beyond the digestive system.

Chronic diarrhea or constipation Bloating and abdominal pain Unintended weight loss 

Genetic Learn More 

](/conditions/celiac-disease)

## Related Articles

[![How Gut Health Affects Your Mood](https://images.unsplash.com/photo-1512621776951-a57141f2eefd?w=1200&h=630&fit=crop&fm=webp)](/mental-health/gut-health-affects-mood)

[](/mental-health/gut-health-affects-mood)[Mental Health](/mental-health)

### How Gut Health Affects Your Mood

2025-11-10

[![The Mediterranean Diet: A Complete Beginner's Guide](https://images.unsplash.com/photo-1498837167922-ddd27525d352?w=1200&h=630&fit=crop&fm=webp)](/nutrition/mediterranean-diet-beginners-guide)

[](/nutrition/mediterranean-diet-beginners-guide)[Nutrition & Diet](/nutrition)

### The Mediterranean Diet: A Complete Beginner's Guide

2026-01-20

## Sources

1.  [The Human Microbiome](https://www.nih.gov/news-events/nih-research-matters/human-microbiome) - National Institutes of Health
2.  [Role of the gut microbiota in nutrition and health](https://www.bmj.com/content/361/bmj.k2179) - The BMJ
3.  [The Gut Microbiome in Health and Disease](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3983973/) - PubMed Central

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In This Entry

[Definition](#definition)[Also Known As](#also-known-as)[Key Facts](#key-facts)[How It Relates To Your Health](#health-relevance)[Related Terms](#related-terms)[Related Conditions](#related-conditions)[Related Articles](#related-articles)[Sources](#sources)

Browse Digestive Terms

[Irritable Bowel Syndrome](/glossary/irritable-bowel-syndrome)[Gastroesophageal Reflux Disease](/glossary/gastroesophageal-reflux-disease)[Peristalsis](/glossary/peristalsis)[Leaky Gut Syndrome](/glossary/leaky-gut-syndrome)[Detoxification](/glossary/detoxification)[Dysbiosis](/glossary/dysbiosis)

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