Gut Hormone INSL5 May Explain 40% of IBS-D Cases.

In 2025, researchers from the University of Cambridge studied patients with IBS-D and bile acid diarrhea, analyzing blood samples for the gut hormone INSL5 using a new test from Eli Lilly. They compared INSL5 levels in healthy people and those with chronic diarrhea.

High INSL5 levels were found in up to 40% of IBS-D cases, linked to bile acid irritation in the colon, causing watery stools. A drug, ondansetron, blocked INSL5’s effects, reducing symptoms in those with high levels. This could lead to a new blood test and treatment.

Ask your doctor about INSL5 testing if you have chronic diarrhea.