What are probiotics?
The term “probiotic” (from the Greek for life) has had a number of different meanings throughout history. Once described as a substance secreted by one microorganism that stimulated the growth of another and later to signify organisms and substances which contribute to intestinal microbial balance. Today, probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit to the host.
Typically, probiotics on the shelf contain freeze-dried or live bacteria or yeasts; most commonly from the genera Lactobacillus and Bifidobacterium. Probiotic organisms can be incorporated into supplements (powders, capsules, tablets, oils, wafers), as well as foods (milk drinks, medicinal yogurts, fruit juices, ice cream).
What are not probiotics?
The early definitions of probiotics were inclusive of traditional fermented foods such as yogurt, sauerkraut, and kefir, but the most recent interpretation of the definition has, somewhat controversially, excluded these traditional ferments. These are now considered food sources of live cultures, but not probiotics themselves.
The reasoning behind this is that these foods are of undefined microbial content. Species and strain composition can differ from batch to batch as well as the number of bacteria present. Additionally, the strains contained in these foods may also lack specific therapeutic qualities (Read The Importance of the Bacterial Strain). They may not provide any health benefit beyond the enhanced nutritional profile of the fermented food. That’s why traditional fermented foods cannot be relied upon for specific therapeutic effects in the same way that probiotics containing well-defined and specific strains, with clinical effects, in precise doses can.