Digestion in the small intestine is the result of complex mechanical and biological phenomena which can be modelled at diff erent scales. In a previous article, we introduced a system of ordinary diff erential equations for describing the transport and degradation-absorption processes during the digestion. The present article sustains this simplifi ed model by showing that it can be seen as a macroscopic version of more realistic models including biological phenomena at lower scales. In other words, our simpli ed model can be considered as a limit of more realistic ones by averaging-homogenization methods on biological processes representation.