microbiome? “I would say the answer to that is likely yes,” Sanders said, but such causality needs to be confirmed. Sanders provided an overview of demonstrated effects of probiotics on the microbiome and on health and scientific challenges to translating this knowledge into probiotic foods.
Impact of Probiotics on the Microbiome
There is plentiful evidence of the effects of probiotics on the microbiome, especially intestinal microbiota (Sanders, 2011). The most common impact of probiotics on the intestinal microbiota, or more accurately the fecal microbiota, is an increase in the particular strain that the test individuals have been fed. Probiotics expand across a wide taxonomic range and even include yeast (i.e., Saccharomyces). However, researchers usually feed their test subjects probiotics that they know will survive intestinal transit. Another common observation is changes in metabolic parameters that can be either local or pan-organismal. These changes can be observed not just in the feces or colon, but also in the urine and in other tissues. Probiotics have also been observed to impact pathogens, as evidenced by changes in the infectivity and toxicity of pathogens. Researchers have also observed changes in the community structure of indigenous microbiota, although results vary among probiotics and among studies. For example, different probiotics have been shown to increase community evenness, functional redundancy, and specific types of potentially beneficial bacteria. Finally, and one of the more interesting effects in Sanders’s opinion, is that probiotics have been shown to encourage homeostasis, or stability, of the microbiota. It has been hypothesized that maintaining the microbiota in an “even state” has beneficial physiological effects; microbiota that maintain a certain evenness, or stability, may be able to rebound more quickly when perturbed by an antibiotic or other stressor (Sanders, 2011).
When considering beneficial effects of probiotics on the microbiome, it must be remembered that experts have yet to reach consensus on what a healthy microbiome looks like. This fact makes it difficult to know which probiotic effects on the microbiome are likely to translate into health benefits for the host.
Demonstrated Health Benefits of Probiotics
The demonstrated health benefits of probiotics go beyond the gut. Researchers have investigated a wide range of end points, including oral microbiology (e.g., dental caries), allergies (e.g., atopic dermatitis, asthma), vaginal infections, mental function, skin microbiology, acute upper respiratory tract infections, and various global end points (e.g., growth parameters of undernourished children, reduced absences from work or day care,