On a well managed farm, you can get 1 cow per 1.25 acres of land, hanging weight about 750lbs. That yields about 750k kcal, which is enough for 2100 calories per day for an entire year.

Nutritionally, you can get all of your fat or protein from 1lb of beef per day. One cow is enough to feed 2 adult humans for an entire year.

This production would require almost zero external inputs. No fertilizer or water, just graze land and water from rainfall.

Just in corn alone, we produce over 10k kcal per person annually in the US. We have a surplus of grains and legumes. We produce an order of magnitude more calories than we need every year.

If you want to solve sustainability, you need to solve waste. To solve waste, you need to fix the incentives. As long as city dwellers demand their cheap industrialized food, taxes will subsidize the cheap industrialized food.