There is actually a scientific hypothesis in ecology called the "ten percent law", introduced by Lindeman in 1942. It explains the incredible inefficiency of energy transfer through trophic levels (producers -> primary consumers -> secondary consumers -> tertiary consumers). The ten percent law states that only 10% of total energy produced by one trophic level is actually effectively consumed by the next trophic level. The other 90% of energy is used for respiration (the storing and retrieving of energy in an organism).
So, in a hypothetical situation, an ecosystem's producers produce 1,000,000 units of energy. Only 100,000 make it to the primary consumers. Of the 100,000, only 10,000 makes it to the secondary consumers. And of the 10,000, only 1,000 make it to the tertiary consumers. A visual representation of this would be called a trophic pyramid; pic related.
Cows and chickens are primary consumers, since they consume plants, mostly. So, at the very least, our food system is more efficient than if we primarily ate wolves, which are secondary consumers. But, it stands that our food system would be much more efficient if we ate only plants. As a global population of humans, we would be able to support a much greater number of people's appetites if we ate wheat, corn, beans, and apples more frequently than chicken, beef, pork, and fish.
However, there would also be the issue of getting ample nutritional needs (after all, humans were intended to both hunt and gather), and sacrificing some quality of life for the public good. Furthermore, you better believe that the top classes of people would pay $400 per ounce of sirloin if that's what it took to get their meat; this solution would only truly work in a more economically equitable society.