I don't think it is an isolated incident. Once something has become "known" among the public and the medical profession, it seems quite difficult to update it. Another example is the dietary cholesterol issue.

The human body is incredibly complex and we have quite limited tools to study it, so we are bound to arrive at wrong conclusions. That by itself is to be expected, but what does really worry me is this missing knowledge updating mechanism. It can take decades for quite a substantial update on what we thought we knew to trickle down from academia to practicing medical professionals.

At this point, if you have any kind of scientific literacy, it might be a good idea to verify whatever your doctor claims.