Anecdotal evidence from someone who's been through some of the worst digestive issues possible (stops in involuntary peristalsis/motility, food not digesting) due to "bad" bacteria being continuously introduced from infection elsewhere: yogurt.

Specifically kefir/filmjölk. Buy a bottle, take a serving in the morning, and at night if you like/can afford.

I've turned my life around. Friends have stopped proton pump inhibitors/antacids like Prilosec/Omeprezole, etc, because of this simple lifestyle switch (one serving per day). I take many more.