In health, there is a balanced distribution across these pathways. However, under conditions of stress,  or microbial imbalance, tryptophan metabolism skews toward excessive kynurenine pathway flux. This shift is detectable in blood as increased kynurenine-to-tryptophan (KYN:TRP) ratio and decreased levels of beneficial indole derivatives like IPA.  

This imbalance not only reflects microbial stress – it amplifies it. Low IPA and high KYN levels are signals of reduced microbial activity and increased immune activation. In contexts of persistent imbalance, this pattern is often observed together with reduced barrier resilience and altered microbial signatures.