Definition of substitution. 1  1a : the act, process, or result of substituting one thing for anotherb : replacement of one mathematical entity by another of equal value. 2  2 : one that is substituted for another.
Homogenized milk is any sort of milk that has been mechanically treated to ensure that it has a smooth, even consistency. The homogenization process typically involves high temperatures, agitation, and filtration, all aimed at breaking down milk's naturally occurring fat molecules.
When you drink non-homogenized milk, your system absorbs native milk-fat globule membrane (MFGM) proteins. These are normally digested in the stomach or gut. However, homogenization decreases the size of milk-fat globules, making caseins the main protein fraction that the body absorbs.