The principal substrate for such proteolysis is casein, but limited degradation of whey proteins
may also occur.15,16 The net effect of this proteolysis is that fermented milks have a
higher content of peptides and free amino acids, especially valine, histidine, serine,
and proline, than milk does.17,18 Moreover, although the limited proteolytic action of
yogurt bacteria does not significantly alter the nutritional value of milk proteins,19
yogurt is significantly more digestible than the milk mixture from which it is made.20
A study with rats demonstrated that feeding yogurt compared to the native milk
from which it was prepared resulted in increased feed efficiency.