Indoleacetic Acid (IAA), also known as indole-3-acetate, is a compound formed through the bacterial fermentation of tryptophan, an essential amino acid obtained from dietary protein. Several gut microbes — including Bacteroides, Clostridia, Escherichia coli, and Saccharomyces species — can convert tryptophan into IAA.
IAA serves as a marker of microbial activity in the gut. Elevated levels may indicate increased bacterial fermentation of protein, often linked to digestive imbalance or intestinal dysbiosis.
High IAA has been observed in conditions such as:
Liver disease
Autism spectrum disorder (ASD)
Certain cancers
When IAA is elevated, it may be helpful to:
Reduce excessive protein intake (to lower substrate availability for bacterial fermentation)
Address gut health issues, including maldigestion, dysbiosis, or impaired intestinal barrier function
While some bacteria produce IAA, others can break it down. Species such as Bacillus subtilis and Pseudomonas aeruginosa are capable of degrading indoleacetic acid, helping maintain balance within the gut ecosystem.
IAA can also be found in various plant-based foods, including:
Lettuce
Cherry tomatoes
Chinese bayberry
Okra
High tryptophan intake or consumption of green and black tea may also influence IAA production through changes in gut microbial metabolism.
Indoleacetic Acid reflects how gut bacteria process dietary protein and tryptophan.
Elevated levels often suggest increased microbial protein fermentation or gut dysbiosis.
Low levels may indicate reduced microbial activity or low tryptophan availability.
Balancing protein intake, supporting healthy digestion, and maintaining a diverse microbiome can help regulate IAA levels.
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- If elevated, decrease protein intake and address digestion and GI issues. Bacteroides, Clostridia, and E. coli ferment tryptophan to produced indoleacetic acid.
- It has been found elevated in liver disease, ASD, and cancer, and has been noted as a marker of microbial activity.
- Indoleacetic acid can be degraded by Bacillus subtilis, or Pseudomonas aeruginosa.
- Elevated IAA in the urine suggests incomplete digestion and absorption of tryptophan in the intestine, allowing colonic bacteria to convert tryptophan to IAA.
- Elevations may also reflect an overgrowth of bacteria acting on tryptophan.
Clinical Associations: IAA elevations and altered tryptophan metabolism have been associated with systemic inflammation, psychologic and cognitive function, autism, and chronic diseases such as cardiovascular disease. Hartnup’s disease, a genetically-linked dysfunction in the transport of freeform amino acids across the intestinal mucosa, can cause severe elevations of urinary IAA.
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Indoleacetic Acid (IAA) is a metabolite of tryptophan, an essential amino acid found in protein-rich foods. It is produced mainly by gut bacteria as they break down tryptophan.
Low levels of IAA generally reflect reduced microbial metabolism of tryptophan in the gut — in other words, your intestinal bacteria are not producing as much of this compound as expected.
Low IAA can occur for several reasons, often related to gut health or nutrient availability:
Low levels of tryptophan or protein intake – not enough dietary substrate for IAA production.
Reduced populations of indole-producing gut bacteria – particularly species from genera such as Escherichia, Bacteroides, and Clostridium.
Altered gut microbiome composition (dysbiosis) – especially when beneficial bacteria are depleted.
Overgrowth of non-indole-producing microbes that crowd out the normal flora.
Rapid intestinal transit or inflammation, which can reduce bacterial fermentation activity.
IAA helps evaluate:
Tryptophan metabolism and its downstream pathways (e.g., serotonin and kynurenine production)
Gut microbial activity and balance
Interactions between diet, microbiome, and immune function
IAA is part of the broader picture of microbial tryptophan metabolism, which plays an important role in gut barrier integrity, immune balance, and mood regulation.
If your IAA levels are low:
Support gut microbiome diversity by increasing intake of plant-based fibers (vegetables, fruits, legumes, whole grains).
Include fermented foods or probiotics that help restore beneficial bacteria.
Ensure adequate protein intake, especially from tryptophan-rich sources (turkey, eggs, dairy, seeds, tofu).
Address any gut inflammation or digestive issues with the help of your clinician.
Low Indoleacetic Acid usually points to a less active or imbalanced gut microbiome rather than a direct health problem on its own. It may suggest reduced tryptophan metabolism by gut bacteria, which can influence both gut and brain health over time.
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I have been using Healthmatters.io since 2021. I travel all over the world and use different doctors and health facilities. This site has allowed me to consolidate all my various test results over 14 years in one place. And every doctor that I show this to has been impressed. Because with any health professional I talk to, I can pull up historical results in seconds. It is invaluable. Even going back to the same doctor, they usually do not have the historical results from their facility in a graph format. That has been very helpful.
Karin
Advanced Plan Member since 2020
What fantastic service and great, easy-to-follow layouts! I love your website; it makes it so helpful to see patterns in my health data. It's truly a pleasure to use. I only wish the NHS was as organized and quick as Healthmatters.io. You've set a new standard for health tracking!
Paul
Healthmatters Pro Member since 2024
As a PRO member and medical practitioner, Healthmatters.io has been an invaluable tool for tracking my clients' data. The layout is intuitive, making it easy to monitor trends and spot patterns over time. The ability to customize reports and charts helps me present information clearly to my clients, improving communication and outcomes. It's streamlined my workflow, saving me time and providing insights at a glance. Highly recommended for any practitioner looking for a comprehensive and user-friendly solution to track patient labs!
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1-Methylhistidine, 1-Methylhistidine (Plasma), 2-,3-, and 4-Methylhippuric acid, 2-Methylhippuric Acid, 2-Methylsuccinic Acid, 3,4-Dihydroxyhydrocinnamic Acid, 3,5-Dihydroxybenzoic Acid, 3-Methylhistidine, 3-Methylhistidine (Plasma), 3-Phenylpropionylglycine, 4-Hydroxybenzoic Acid, 4-Hydroxyphenylacetic Acid, 4-Hydroxyphenylpyruvic Acid, 5-Hydroxyindoleacetic Acid, 8-Hydroxy-2'-deoxyguanosine, a-Hydroxybutyric Acid, a-Keto-b-methylvaleric Acid, a-Ketobutyric Acid, a-Ketoglutaric Acid, a-Ketoisocaproic Acid, a-Ketoisovaleric Acid, a-Aminoadipic Acid, a-Aminoadipic Acid (Plasma), Adipic Acid, Alanine, Alanine (Plasma), Aldosterone, Anserine, Anserine (Plasma), Anthranilic Acid, Arabinitol, Arginine, Arginine (Plasma), Arginosuccinic Acid, Arginosuccinic Acid (Plasma), Asparagine, Asparagine (Plasma), Aspartic Acid, Aspartic Acid (Plasma), b-Hydroxybutyric Acid, b-Hydroxyisovaleric Acid, b-Alanine, b-Alanine (Plasma), Benzoic Acid, Benzoylform, Branched Chain Alpha-Keto Organic Acids, Carnosine, Carnosine (Plasma), cis-Aconitic Acid, Citric Acid, Citrulline, Citrulline (Plasma), Cortisol, Cortisone, Creatinine, Cystathionine, Cystathionine (Plasma), Cystine, Cystine (Plasma), D-Lactic Acid, Equol, Ethanolamine, Ethanolamine (Plasma), Ethylmalonic Acid, Formiminoglutamic Acid, Fructose, Fumaric Acid, g-Aminobutyric Acid, g-Aminobutyric Acid (Plasma), Glucaric Acid, Glucose, Glutamic Acid, Glutamic Acid (Plasma), Glutamine, Glutamine (Plasma), Glutamine / Glutamate Ratio, Glutamine / Glutamate Ratio (Plasma), Glutaric Acid, Glycine, Glycine (Plasma), Glycylproline, Glycylproline (Plasma), GSG Index, Hexanoylglycine, Hippuric Acid, Histidine, Histidine (Plasma), Homocitrulline, Homocitrulline (Plasma), Homocystine, Homocystine (Plasma), Homogentisic Acid, Homovanillic Acid, Hydroxykynurenine, Hydroxyproline, Hydroxyproline (Plasma), Indoleacetic Acid, Isocitric Acid, Isoleucine/allo-Isoleucine, Isoleucine/allo-Isoleucine (Plasma), KT Ratio, KT Ratio (Plasma), Kynurenic Acid, Kynurenine, Kynurenine (Plasma), Lactic Acid, Leucine, Leucine (Plasma), Lysine, Lysine (Plasma), Malic Acid, Mandelic Acid, Methionine, Methionine (Plasma), Methylmalonic Acid, Microalbumin, Ornithine, Ornithine (Ornithine transcarbamylase), Ornithine (Plasma), Orotic Acid, Oxalic Acid, pH, Phenylacetic Acid, Phenylalanine, Phenylalanine (Plasma), Phosphate, Phosphoethanolamine, Phosphoethanolamine (Plasma), Picolinic Acid, Pimelic Acid, Proline, Proline (Plasma), Pyridoxic Acid, Pyroglutamic Acid, Pyruvic Acid, Quercetin, Quinolinic Acid, Sarcosine, Sarcosine (Plasma), Sebacic Acid, Serine, Serine (Plasma), Suberic Acid, Suberylglycine, Succinic Acid, Sulfocysteine, Sulfocysteine (Plasma), Tartaric Acid, Taurine, Taurine (Plasma), Threonine, Threonine (Plasma), Total Branched Chain Amino Acids, Total Branched Chain Amino Acids (Plasma), Tryptophan, Tryptophan (Plasma), Tyrosine, Tyrosine (Plasma), Valine, Valine (Plasma), Vannilylmandelic Acid, Xanthurenic Acid
