Long ago I fuzzily recall reading some info on the process for some of these studies.

First there's the questionnaire about what someone ate for a whole month or even year. To me that's satire.

Then there's the categorization. For example, meats are considered high fat, and by the way so are donuts and desserts. Anything that puts these in the same category as if amino acids and sugar don't matter is imo more satire.

Then there's the assumption. E.g. if you eat a lot of baked goods (sugars and/or grains), you're eating a lot of eggs because there's usually an egg in those somewhere.

There's a book called "Doctoring Data" by Malcolm Kendrick. It is deliberately written to the layman, and has his brand of humor. It's really a good read though, and gives insight into a variety of studies and claims. By the time I was done I realized that you pretty much can't believe anything at this point, unless you either have some experience knowing what to look for, or follow some person who blogs and who does, and will walk through it.

(I have it on kindle, and I can loan it for 14 days (to one person only). Anybody who wants to read it and not $buy it I'm happy to do that. Note that you don't need kindle only an amazon account, you can read it in a browser as well. First to request send me DM. :-))

PJ