With the release of the eighth edition of the U.S. government’s Dietary Guidelines expected by year’s end, it seems reasonable to consider—with the “obesity plague” upon us and Americans arguably less healthy than ever before—whether the guidelines are to be trusted and even whether they have done more harm than good.

Many Americans have lost trust in the science behind the guidelines since they seem to change dramatically every five years. In February, for example, the Dietary Guidelines Advisory Committee declared that certain...