[Mirioron]

While it's an interesting idea, this only captures relative wealth. Places that have higher quality food as standard would be seen as less rich. It's much cheaper to get calories from staples such as rice and potatoes, but a lot more difficult to get it from protein. It's possible to survive on a diet of mostly carbs and little protein, but that can also make you more susceptible to malnutrition, especially if famines are abound.

Also, 3000 kcal per day means that everyone gets fat. The amount of intense physical activity you have to do for an average person to use up that many calories is on the level of modern athletes.

[notechback]

Just to mention that staples like grain have indeed much protein, so your sentence actually doesn't make much sense.

The conception of food consisting of vegetable + meat/fish + staple (rice, bread, potato, ..) is an utterly modern one.

All across history in most settled cultures will have lived principally of local plants of some kind, with meat being a rate treat. The exception being fishing villages but even there vegetables/grains will always have been a principal source of calories and nutrients.

[Mirioron]

Yes, and people nowadays are taller, smarter, and live longer. A large part of the Flynn effect is usually attributed to nutrition. Humans can survive with poor nutrition (not getting the right amount of nutrients they need) for a very long time, but it usually has consequences, especially when it happens during childhood.

Another thing to keep in mind is that humans didn't evolve to be farmers. We evolved to be hunter-gatherers. Just because for a slice of our existence people ate one way doesn't mean that that's the diet most suited for us.

By the way, there's a difference between animal proteins and protein in grain. They aren't quite the same composition of amino-acids.