Acid‐insoluble ash as a marker compound for use in digestibility studies with humans

The study aimed to evaluate acid‐insoluble ash, in the form of added celite (a diatomaceous earth), as an indigestible marker compound for use in digestibility studies with humans. The study comprised two parts. First, the recovery of dietary acid‐insoluble ash in the faeces was determined in a controlled 10‐day metabolism study involving five 6‐week‐old male pigs receiving food consisting of ingredients commonly eaten by humans. Secondly, the faecal recovery of dietary acid‐insoluble ash was determined with six adult humans following a set diet which maintained their normal levels of daily food intake for 7 days. The mean (±SE) recoveries of dietary acid‐insoluble ash in the faeces of the pigs and human subjects were 90·0 (±2·24) and 92·1 (±4·59)%, respectively. The mean apparent faecal digestibility coefficients for dietary dry matter were not significantly different (P > 0·05) when determined by total faeces collection or by reference to the marker, in both species. It was concluded that celite is a potentially useful dietary marker compound for use in human digestibility studies involving collection of faeces. The marker was readily accepted by the human subjects and can be determined chemically using simple gravimetric analysis.