system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does the 'good bacteria' in Yogurt or Sauerkraut survive gastric acids? what percent of it is alive before reaching the gut?
gpt
The bacteria in question have adapted to live in acid environments and even make their environments sour in order to kill off other bacteria so they can consume all the nutrients. So they have an easier time getting through the gastric acid then most bacteria. And you are right that the gastric acid is not fully efficient and some bacteria will get through. It is hard to count these and there are a lot of variables involved. But some bacteria might be in a clump of yoghurt that does not dissolve before it goes straight through your stomach. Or the bacteria might be able to hide in the crevices of the musli you eat with it. On the other hand adding sugar or grain to the yoghurt before eating it can get the bacteria to come out of hibernation and take down their protective shell making them less resistant to the acid. But the stomach is not the only thing protecting you from bacterial infections. The existing gut flora will attack any new bacteria. So when the stomach acid have gotten rid of most of the bacteria the rest will be easy for the gut flora to handle. So even though yoghurt might help replace a weak gut flora we would not expect it to have any effect on normal people.