Honestly I thought that was pretty well known already. I knew a girl in college about 20 years ago who had been on massive amounts of anti-biotics, and it ruined her stomach & digestive system in some way. At the time she was having to slowly build up "good" bacterial through some type of specialty yogurts (might just have been probiotics, which were not as prevalent then). It was a multi-year process though, and she couldn't eat a lot of types of food in the meantime.