What makes tryptophan unique is that it sits at a metabolic crossroad between:
 

• Microbial metabolism, where gut bacteria convert it into indole derivatives like IPA with immune-balancing, antioxidant, and barrier-supportive effects. 
• Host metabolism, where tryptophan can be used for producing serotonin (important for mood and gut motility), or diverted into the kynurenine pathway during immune stress and activation. 

Because tryptophan can be used in so many ways, its availability and distribution reflect important aspects of gut and immune function. For example: 

• Low TRP levels might indicate increased use by the host, such as during immune stress when more is directed into the kynurenine pathway.  
• High TRP levels with low IPA may suggest reduced microbial conversion. 
• Balanced TRP with favorable ratios suggests efficient microbial contribution and lower levels of immune stress. 
   

Why tryptophan is measured in our Gut Health Test

• It’s a baseline marker – used to interpret both the IPA:TRP and KYN:TRP ratios
• It reflects dietary intake, systemic availability, and shifts in metabolic demand
• It helps contextualize whether the microbiota or immune system is dominating tryptophan metabolism
   

The way tryptophan is used in the body offers valuable insight into gut microbial function and immune-metabolic balance.

Quick summary

• TRP is the dietary precursor to all measured pathways – IPA (from the indole pathway) and KYN (from the kynurenine pathway). 
• Its levels and direction of use give context for how tryptophan is being metabolized in the body. 
• A balanced TRP level with healthy ratios signals active microbial contribution and lower immune stress.