One of the reasons is that health-related academic research is often wrong.
Biostatisticians have studied the question of just how frequently published studies come up with wrong answers. A highly regarded researcher in this subfield of medical wrongness is John Ioannidis, who heads the Stanford Prevention Research Center, among other appointments. Using several different techniques, Ioannidis has determined that the overall wrongness rate in medicine’s top journals is about two thirds, and that estimate has been well-accepted in the medical field.
This excerpt is taken from a longer article titled “‘Survival of the wrongest’ How personal-health journalism ignores the fundamental pitfalls baked into all scientific research and serves up a daily diet of unreliable information.” The article is interesting throughout and merits a full reading.