Clinical Studies of Probiotic Agents

The deliberate addition of microorganisms to the diet of humans dates back to ancient times. Initially, these were probably ingested in the form of fermented milk products, where the bacteria were used to preserve dairy foods. The popularity of dairy products containing "cultures," in the form of yogurt and other fermented milks, has not only withstood the test of time, but their consumption has actually increased over the last few decades due to numerous factors. The recent increase in health consciousness of some populations and the purported health benefits touted in the lay literature and popular culture have boosted this popularity. The concept that these products confer health benefits beyond their dietary value is not new (1). The idea that microorganisms are part of our environment and that our intestinal lumen is a continuum with that environment led individuals like Metchnikoff (2) around the turn of the century to suggest that the ingestion of specific organisms (lactobacilli) could displace toxin-producing "putrefactive" microorganisms in the intestinal tract and thus promote health and prolong life. Later in this century, the concept that preserving a normal gut flora was beneficial ensued. Subsequently, other important clinical roles of normal gut flora were described. A "healthy" flora is necessary to maintain the health of the intestine, particularly the colon, to prevent the establishment or activity of potential pathogens and maintain adequate nutritional status of the B vitamins and vitamin K. Eventually, a scientific literature emerged, supporting the potential of some of these microorganisms to prevent or treat specific disease conditions when consumed orally, both in animals and in humans (3,4). All this led to the current concept of "health-promoting bacteria."