Yogurt and immunity: The health benefits of fermented milk products that contain lactic acid bacteria

The history of fermented milk products is long and quite diverse culturally. Although the exact origins are difficult to ascertain, they likely date back to more than 10,000 yr ago. According to Persian tradition, Abraham owed his fecundity and longevity to the regular ingestion of yogurt. In the early 1500s, King Francis I of France was reportedly cured of a debilitating illness after eating yogurt made from goats’ milk.1 Scientific interest in the health benefits of yogurt was initiated by Élie Metchnikoff in the early 1900s. Metchnikoff proposed that the lactic acid microbes of fermentation must be antagonistic to the putrefying microbes of the gut, and once introduced into the intestine, they would prevent the breeding of the noxious microbes that required an alkaline environment. His hypothesis was stimulated by the fact that populations such as those living in the Balkans regularly ate yogurt and were noted for their longevity. He experimented on himself and reported that his health, which was generally poor, improved with regular ingestion of sour milk prepared with cultures of the Bulgarian lactic bacillus. Metchnikoff’s enthusiasm about yogurt became more publicized, and doctors began recommending yogurt or sour milk as a hygienic food. Metchnikoff credited his relatively long life in part to the lactic bacilli in his diet, and hypothesized “When people have learnt how to cultivate a suitable flora in the intestines of children as soon as they are weaned from the breast, the normal life may extend to twice my 70 yr.”² (See Chapter 1 for more details on the history of yogurt.).