The Metabolites We Test

Indole-3-Propionic Acid (IPA)

Indole-3-Propionic Acid (IPA)

  • Indole-3-Propionic Acid (IPA) has been associated with brain, kidney, and heart health*.
  • IPA is produced in the human gut exclusively by one particular species of gut bacteria (Clostridium sporogenes) from tryptophan27. Thus, IPA is a critical marker for a healthy gut microbiome.
  • IPA is considered one of the strongest antioxidants identified*. IPA has been shown to play an important role in brain health28.
  • IPA plays a crucial role in maintaining a healthy gut by strengthening the tight junctions (contact) between cells lining the gut54. This is important for maintaining intestinal structural integrity, and decreasing intestinal permeability.
  • IPA can be found in some sprouted seeds, such as mung beans and chickpeas.
Indole-3-Lactic Acid (ILA)

Indole-3-Lactic Acid (ILA)

  • Indole-3-lactic acid (ILA) is linked with the formation of downstream metabolites such as indole-3-propionic acid (IPA).
  • ILA is a tryptophan metabolite and precursor to indole-3-propionic acid (IPA)29.
  • The tryptophan pathway is heavily involved in the creation of neurotransmitters and antioxidants that are important to healthy brain and gut function.
  • ILA is found in fermented veggies such as kimchi, sauerkraut, pickles and kefir.
Indole-3-Acetic Acid (IAA)

Indole-3-Acetic Acid (IAA)

  • Indole-3-acetic acid (IAA) is a precursor to other metabolites in the tryptophan branch, specifically indole-3-propionic acid (IPA). The tryptophan pathway is heavily involved in the creation of neurotransmitters (such as serotonin) and antioxidants that are important for healthy brain and intestinal function*.
  • Proper levels of IAA maintain healthy levels of the beneficial Lactobacillus species of gut bacteria, which converts sugars such as glucose and fructose to lactic acid30.
  • IAA can be produced from indole-3 pyrurate, which is a precursor to indole-3-propionic acid.
  • IAA is an auxin (growth hormone) produced in plants.
  • IAA has been shown to possess antioxidant activity31*.


  • Tryptophan levels are linked to the ability to fall asleep and to muscle health. Tryptophan has been linked to mood and is important for emotional well-being*.
  • Tryptophan is obtained mainly through one’s diet. Certain gut bacteria are also capable of making tryptophan.
  • Tryptophan is an amino acid. Amino acids are building blocks for proteins that are essential for maintaining a healthy body*.
  • Tryptophan is the precursor to many important metabolites: kynurenine, serotonin, and indole-3-propionic acid.
  • Tryptophan can cross the blood-brain barrier, making it available to produce important neurotransmitters like serotonin32 which are essential for normal brain processes that affect mood, behavior, memory, and learning33*.
  • Tryptophan is found in foods such as cruciferous vegetables, bananas, eggs and meat.


  • Serotonin is linked to the ability to fall asleep, muscle health, brain health and gut health34.
  • Serotonin is a tryptophan metabolite. Serotonin synthesis is facilitated by the adequate presence of vitamins B1, B3, B6, and folic acid. The tryptophan pathway is heavily involved in the creation of neurotransmitters (such as serotonin) and antioxidants that are important to healthy brain and gut function*.
  • Serotonin is one of the most important signaling molecules within the gut, where it plays a pivotal role in initiating secretions (mucosal) and motor reflexes (the movement of the intestine)35, and is crucial for normal functionality of the central nervous system*.


  • Kynurenine is linked with levels of downstream metabolites (kynurenic acid) and vitamin B3. Kynurenine has been linked with energy levels and gut health. Kynurenine production is mediated by vitamin B6, selenium and sulfur amino acids.
  • Kynurenine is used in the production of niacin (vitamin B3). Niacin is considered to be one of the essential human nutrients where it helps maintain integrity of DNA*.
  • Kynurenine is a metabolite of tryptophan. Its primary function is to dilate blood vessels*. It is also a regulator of the immune system36-37.
  • Kynurenine is utilized by the endocrine system to produce certain hormones*.
  • Kynurenic acid, a metabolite of kynurenine, is a neuroprotective agent in the brain38.
  • Kynurenine in the eye filters UV radiation*.
  • Kynurenine can be found in meat, cheese, cruciferous vegetables, bananas, plums, and kiwi.
Indoxyl Sulfate

Indoxyl Sulfate

  • Indoxyl sulfate (IDS) is linked to oxidative stress in numerous cell types including: vascular smooth muscle cells, endothelial cells, and bone cells39.
  • IDS is a metabolite of tryptophan and is absorbed into the blood from the liver. IDS has been associated with kidney and heart health39.


  • Tyrosine is linked to gut and brain health5,40,41.
  • Tyrosine is a nonessential amino acid, which means that an individual can synthesize it from another amino acid, phenylalanine.
  • Tyrosine functions as a building block for several important neurotransmitters such as dopamine, epinephrine, and norepinephrine. Neurotransmitters regulate mood, behavior, and general feelings of well-being*.
  • Tyrosine is essential for the thyroid gland to produce hormones T3 and T4 (which regulate growth, metabolism, body temperature, and heart rate)41,42.*
  • Tyrosine is also an important amino acid for the pituitary gland. The pituitary gland, like the thyroid gland, controls metabolism and growth; additionally, it regulates sexual maturation, reproduction, blood pressure, and many other vital physical processes41,43*.
  • Tyrosine is also necessary for cell division44,45*.
  • Tyrosine is present in almost every protein in the body41.
  • Tyrosine can be found in soy, meat, cheese, nuts and seeds.


  • Xanthine plays a role in inducing digestive enzymes. Xanthine levels are linked to heart rate and heart health46.
  • Xanthine is a metabolite of the purine pathway and functions in the digestive tract to induce hydrochloric acid production and promote secretion of pepsin from cells lining the stomach. Both of these processes help to break down consumed food47*.
  • Xanthine is a mild stimulant and is found in coffee, cola, and green tea*.


  • Metabolites of the purine pathway are significant because they affect both the gut and the brain. In the gut, 3-Methylxanthine (3MXAN) increases hydrochloric acid and pepsin secretion, which aid in digestion*. Purines are key components of cellular energy systems (e.g., ATP and NAD), cellular signaling, and along with pyrimidines are involved in RNA and DNA production47*.
  • 3MXAN levels are linked to intake of caffeine.
  • 3MXAN is a purine metabolism-breakdown product in caffeine and theophylline49.
Uric Acid (UA)

Uric Acid (UA)

  • Uric acid is a final product of purine metabolism. Metabolites of the purine pathway are important because they affect both the gut and the brain. In the gut, uric acid increases hydrochloric acid and pepsin secretion aiding in digestion.* Purines are key components of cellular energy systems (e.g., ATP and NAD), cellular signaling, and along with pyrimidines are involved in RNA and DNA production48*.
  • Uric acid levels are correlated with hydration and purine levels in the diet. Approximately 1/3 of purines are derived from food. The majority of uric acid is dissolved in the blood, filtered through the kidneys, and expelled in the urine.
  • Fructose tolerance is linked to uric acid levels.
  • Uric acid may be a marker of oxidative stress50.
  • Uric Acid is found in cherries, blueberries and apple cider vinegar.

*These statements have not been evaluated by the FDA. These products are not intended to diagnose, treat, cure or prevent any disease.


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