The WHO is a 71-year-old UN agency whose constitution has been signed by 61 countries. One of the organizations it incorporated was the Office International d'Hygiène Publique (https://en.wikipedia.org/wiki/Office_International_d%27Hygi%...), an international public-health organization.

I have to say I find your pushback at the term "official" perplexing. Why do you disagree with this descriptor? They're literally official. It doesn't get more official than this. Sure, they're sometimes wrong, as your fat-free reference suggests, but that's beside the point.