As far as I can tell low carb is fully accepted in psychiatric treatment, fairly accepted in diabetics, proven in weight loss but not widely prescribed, and nearly never used by for profit weight loss organisations because it's so easy to DIY without any special products

Researchers have also noticed that they can get a thousand zero carb eaters from Reddit with high adherence to animal sourced food only, and likewise vegans and vegetarians since we separate ourselves so well, so some good epidemiological research is possible where you can actually compare some hundreds of people who eat only meat to others who eat only plants

It would probably be fairly straightforward to compare the spectrum from vegan through vegetarian, pescatarian, SAD, keto, ketovore, carnivore and all the shades of grey I missed though we're probably unique in our ability to say exactly what we ate every day for years

There's also so much money in the chain between a farm full of wheat to a box of highly processed "food", compared to the simple path of meat varying from cheapest self harvested, self butchered, self stored through to using a professional butcher who buys from a meat packing plant through to the most expensive - supermarket meat

Money plus religion versus reality