Indoleacetic Acid

- 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.

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.

Possible Causes of Low Levels

Low IAA can occur for several reasons, often related to gut health or nutrient availability:

1. Low levels of tryptophan or protein intake – not enough dietary substrate for IAA production.

2. Reduced populations of indole-producing gut bacteria – particularly species from genera such as Escherichia, Bacteroides, and Clostridium.

3. Altered gut microbiome composition (dysbiosis) – especially when beneficial bacteria are depleted.

4. Overgrowth of non-indole-producing microbes that crowd out the normal flora.

5. Rapid intestinal transit or inflammation, which can reduce bacterial fermentation activity.

Why It’s Tested

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.

What You Can Do

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.

Key Insight

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.

- A product of tryptophan fermentation. 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.

- Indoleacetic acid has been found in many foods, such as lettuce, cherry tomato, Chinese bayberry, and okra.