>It takes minimum 1 acre of land to feed an adult
No it doesn't. Potatoes are 15 million calories an acre at the low end of yields. That's enough to feed 20 people. At the high end you get twice that. How much land it takes to feed a person is entirely dependant on what that person wants to eat. I grow a balanced diet of meat, dairy, eggs, grains, potatoes, fruits and vegetables for five people on two acres, and I'm not using all that space and I choose to grow low efficiency things like berries because we like them.