Not who... What. It is undoubtedly caused by bad genes. When one spews out nonsensical dietary advice like they actually know what they are talking about, then they must have been born with some bad genes. It could be any number of bad genes that make one predisposed to being arrogant 'know it alls', too big for their britches (but only metaphorically, of course), holier than thou experts on the subject.

If I've learned anything these past four years... Be skeptical of expert opinion. It is mostly just opinion, snatched from their be-hind or last nights evening news.