Based on what I know about the words "professor" and "emeritus" and "cornell", I assume this is written by an authority in the field of nutrition.

The value of being an authority in a field is that you can accurately convey the consensus within that field. Whenever consensus within a field does not exist, the ancient injunction against "argument from authority" remains true. The "authority" derives not from the authoritative individuals themselves, but the collective wisdom of the field to which they've been exposed.

Who says there is no consensus? Given that he's a nutrition science authority, and that other nutrition science authorities aren't refuting him, that's some small evidence that he's representing a consensus (there are other possible explanations as well, that I touched on in my OP).