What formations of probiotic supplements are able to survive stomach acid? One theory advanced by Ripley is that taking them with resistant starch helps. I read on Wikipedia that the gut has 100 trillion bacteria. Makes you wonder how a supplement with a few billion is going to do much, even more so if they are largely destroyed in the stomach. Gut bacteria are established very early in an infant and some features are set for life, although from my reading it looks like many things can alter the ratio of organisms (gaining and losing weight, use of antibiotics).