Holford is the worst sort of charlatan: he sincerely believes his own fantasies. And sincerity sells. He couldn't possibly be trying to con you, could he? His claims to expertise have been exposed by reputable scientists who - unlike Holford himself - have no axe to grind, no pills to sell, no business to run. There are entire websites dedicated to debunking him.
I work with Alzheimer's patients and their carers; I meet experts in the field on a regular basis. These people know that if Alzheimer's were in any way preventable the NHS would be busting a gut to prevent it; and they wouldn't give Holford the time of day.