The action of hydrochloric acid in the process of digestion is largely, if not entirely, due to the number of free hydrogen ions present. Various foods, especially milk, have the property of binding large amounts of acid and converting the hydrogen into a nonionized form, thus to all intents and purposes neutralizing the acid. When foods of the type mentioned are given, much of the hydrochloric acid secreted is rendered inactive. Substances that thus reduce the hydrogen ion concentration are commonly termed "buffers." It has been demonstrated that the buffer value of cow's milk is considerably greater than that of human milk. Therefore the former neutralizes a larger amount of the hydrochloric acid of the stomach secretion. The resultant effect is an interference with the activity of the gastric enzymes through a reduction of the gastric acidity below the optimal hydrogen ion concentration zone of ph 3.5 to 5.0.
ACIDIFIED MILKS. JAMA. 1926;86(22):1698-1699. doi:10.1001/jama.1926.02670480028011