Being a trained intestinal-flora-therapist (and herbalist), maybe I can share some thoughts. As far as I know the probiotic bacteria will mostly survive the stomach when they're in a 'budding' state, meaning just starting to develop.
This occurs in supplements with freezedried bacteria when you dissolve them in water for a couple of minutes; it will also be present in live yoghurt because all forms (budding, fully grown, died) logically are.
As someone else said above; supplements are just what they are: supplements. It would be better to have everybody eat fermented foods *way* more often, but most often, that sadly just isn't the case.
I mainly use them in my patients for 3 reasons:
- their intestinal flora has often been destroyed or outbalanced beyond the reach of normal healing through fermented food
- I mainly treat children, who are not always keen on eating ferments (as are the parents not always keen on putting the time and effort into making them)
- not all bacteria that may be necessary, are usually present in a healthy ferment. Bacteria such as Enterococcus sp. and E. coli sp., may be necessary to enhance the immune system and the intestinal environment. This is necessary, because the probiotic bacteria first need a 'friendly environment' to be able to colonize properly. A *lot* of people have a not-so-friendly intestinal environment, causing their floras to decline.
Apart from that, the living bacteria are not the only benefit from ferments. Their 'poop' (metabolites) is also very beneficial, as it helpes to create forementioned friendly environment. This is probably why people are still experiencing benefit from pasturized / heated yoghurt: doesn't contain any alive bacteria anymore, but it still contains the metabolites (lactic acid).