Regulate the supply side with land use restrictions and restoration of natural habitat; introduce subsidies for underdeveloped and emerging economies to prevent further ecosystem degradation out of economic necessity.
With a set limit on land use, market prices would adjust accordingly (i.e. meat price rises), consumption will reduce (accompanied by some whining) and food innovators get more time and market share for sustainable alternatives.
Anyway, what is your solution? Starvation doesn't seem like an option.