The table shown below is a part of the handout I use for my "Global Imperative for the Local Garden" presentation.
As you examine the information, pay particular attention to the amount of grain (and therefore land) that the typical American diet requires per person per year. It is about four times that of a mainly plant-centered diet typical of many developing countries.
For the time being, the Mediterranean diet seems to be a wiser choice, from a health, longevity, and sustainability perspective.
An exclusive plant-centered diet, for most of humanity, is an economic necessity. It would also be the model if we were trying to see how many humans we could support (probably temporarily) on Earth.
The Mediterranean diet is diversified, healthier, and more easily satisfied by what can be grown by an individual or family in a backyard garden.