Pretty much this. I've been wondering if any of the yogourt and other "health" foods containing living probiotic cultures survive digestion to populate our intestines? If so, is there peer-reviewed evidence you could point me to?
Apparently, some do and some don't.
I just tried searching for yogurt lactobacillus survival on Google, and the first hit I got was an article titled "Survival of yogurt-containing organisms and Lactobacillus gasseri (ADH) and their effect on bacterial enzyme activity in the gastrointestinal tract of healthy and hypochlorhydric elderly subjects" by Pedrosa et al. (1995), published in the American Journal of Clinical Nutrition, vol. 61, pp. 353–359. The abstract reads:
Here's another result from the same search, "Survival and therapeutic potential of probiotic organisms with reference to Lactobacillus acidophilus and Bifidobacterium spp." (PDF) by Kailasapathy & Chin, Immunology and Cell Biology (2000) 78, 80–88, which says:
but also points out that, for survival in the gastrointestinal tract to matter, the bacteria must first survive long enough to get there:
When I took Microbio we had a entire lecture on this. My professor's view was that they do not survive due to the pH of the stomach. He told us that there are microbiologist on both sides as to whether they do make it to the intestine (or enough of them to make much difference) or that they do survive and help. I have added a link below to a article by the American Society of Microbiology. Here it is saying that it may be helpful, but that more studies are being conducted.