Iso fatty acids (branched-chain fatty acids)

Iso fatty acids are branched-chain fatty acids – mainly isobutyrate and isovalerate. They are formed when gut bacteria break down protein: isobutyrate from the amino acid valine, isovalerate from leucine. They are measured in stool together with butyrate, acetate and propionate (analysis “Short-chain fatty acids (SCFA)”).

What iso fatty acids indicate

Unlike the other short-chain fatty acids, iso fatty acids do not come from fibre but from bacterial fermentation of protein (putrefaction), which takes place mainly in the far end of the colon. This also produces ammonia, phenols, indoles and hydrogen sulphide. Iso fatty acids are therefore a measure of how much protein is broken down by bacteria in the colon.

Low iso fatty acids – what does it mean?

Low levels are generally considered unproblematic: they show that little protein is fermented in the colon – typical of a high-fibre diet.

High iso fatty acids – what does it mean?

Raised levels point to increased protein fermentation. Possible reasons are a high-protein, low-fibre diet, stool remaining in the gut for a long time (constipation) or incomplete protein digestion in the small intestine, for example with reduced pancreatic function – more protein then reaches the colon. Foul-smelling wind may go along with it; indican and skatole in urine complete the picture.

The interpretation is given in your report.