Between the vitamin D error (this affected US and Europe and probably more places) and the sodium/blood pressure study that was misleading if not outright false, it's amazing how a few data points can become widespread advice without much verification and follow-up.

I'm sure there's tons more cases that we don't even know about, not in the conspiracy sense, but more in the sense that there's some issues with how carefully these claims are validated before they get put out there as a rule to be followed.