In practice it doesn't work exactly like that. People can't really eat grass, but ruminants can, and many northern climates have lots of grassy plains, which is one of the reasons countries like the Netherlands etc have so many cows. They serve as "intermediaries", converting the grassy plains into a form which humans can eat. Not that people used to eat as much meat as they do now, but it did influence the greater importance of beef etc in their diet compared to some other places.

Facts B. Jewish is my rap name from high school