The concept of manipulating microflora to enhance the positive aspects of the GI tract has become a more focused endeavor. However, this concept is not new. The early recognition of fermented foods offering health benefits dates back to the early 1900s. Eli Metchnikoff was the first to recognize this benefit when he observed the long lives and good health of Bulgarian peasants and associated this with the large amounts of milk soured with lactic acid bacteria (LAB) they consumed.
Since then much study of the health benefits from introduction of orally supplemented beneficial bacteria has taken place. This concept has been termed probiotics and is defined as the consumption of microbes that confer a positive effect on the host in prevention and treatment of specific pathologic conditions. Bifidobacteria, Lactobacillus, and Streptococcus thermophilus have been the most recognized and studied probiotics because of their ability to survive the upper GI tract and proliferate, although transiently, in the colon. The purported health benefits of these and other probiotics include prevention and treatment of diarrhea (particularly rotaviral and antibiotic associated), improved lactose digestion, enhanced gut immune function, and, most recently, prevention and treatment of food allergy and its systemic effects (atopic dermatitis and possibly gastrointestinal allergic disease). Use of probiotics to beneficially alter flora composition and its effects will be elaborated on in a separate chapter.
The effects of probiotics on the host are transient and without regular consumption of these products the colon cannot maintain the level of beneficial colonization that connfers the health benefits. Therefore, a key to the probiotic effect and possible enhancement of native colonic flora would be a substrate for gut bacterial growth through fermentation. Certain dietary carbohydrates and fibers that escape digestion in the upper GI tract are ideal for this action. This recent concept involving such carbohydrates is termed prebiotics.
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