How do you decide what food is "healthy", especially when the science changes?

Keeping up with the best, most up-to-date nutrition information that's backed by science isn't always easy. Just recently, a study that spruiked the benefits of apple cider vinegar for weight loss was retracted.

But is the genie already out of the bottle? How hard is it to unpick scientific research that people have already been told is good, when it in fact goes bad?