A 2026 study in Liver International asks whether the severity of fatty liver can be read from the stool, and the answer points at two enzymes called cathepsin B and S. In 95 patients with MASLD compared against 18 healthy controls, faecal cathepsin activity ran higher in the disease group, and cathepsin B climbed further still in the inflamed MASH form. The activity also tracked with liver enzymes, steatosis, and liver stiffness - the stool, in other words, was reflecting the liver.
The reason this matters is that liver assessment right now leans on imaging and blood tests, and a stool-based signal would be a genuinely different, non-invasive angle. The study does not hand anyone a home test - it is a first look at whether intestinal cathepsins could serve as a marker - but it is the kind of finding that opens a door rather than closing a case.
What the cathepsins are doing there
Cathepsins are a family of enzymes that break down proteins, and the liver versions are already known to push inflammation, cell death, and fibrosis. What the study adds is the gut side: the same enzymes are active in the intestine, and their faecal activity rises with liver disease. The connection is the gut-liver axis again - the intestinal environment is not separate from the liver, and its enzymes read the disease happening upstream.
The microbiome also showed up in the result. The study found the gut microbiome composition differed between people with low and high faecal cathepsin activity, which loops the finding back into the same story the field keeps telling: the gut, its microbes, and the liver are one system, and a stool marker is a window into that system.
The food side of the same system
The actionable part is the part that does not change across these studies: the gut environment responds to the plate, and the Recommended column is the food that keeps it healthy. Fiber feeds the bacteria, plants bring the polyphenols, fermented foods support the microbial balance, and fatty fish brings omega-3s. These are the levers a reader controls, and a stool-marker study is one more reason they matter.
The specific numbers keep it concrete. Rolled oats sit in Recommended at about 10 grams of fiber per 100 grams; legumes and vegetables bring the fermentable fiber; salmon carries omega-3s at roughly 1.3 grams of saturated fat per 100 grams. None of this changes a cathepsin number by tomorrow - the point is that the gut side of the axis is a food-responsive environment, and the pattern is how a reader tends it.
How our editorial team read this
We read biomarker studies with a rule about not turning a signal into a product. Our data editor verified the study size and the enzyme findings, kept the framing on "a first look, not a test," and did not suggest a reader order or track cathepsins on their own. We also kept the causality honest - the study shows association, not that gut cathepsins drive the liver disease.
What we did do is place the finding inside the gut-liver pattern the database already supports, so the reader walks away with the one actionable thing: the plate that tends the gut environment. The honest line is that the stool may one day read the liver, and until then the food is the lever.
The practical takeaway
For someone with fatty liver, the cathepsin study is a glimpse of the future - a possible stool marker - not a test to order today. The Recommended column is the part a reader controls, and it is the same food that tends the gut-liver system the study is mapping.