Given that it takes 10,000 calories of feed to make 1,000 calories of beef, you're still talking about a massive reduction in the number of vegetation calories produced.

Is it calories or mass? I.e. cow eats 10kg of grass to produce 1kg of beef, we eat 10kg of beaf to gain 1kg of weight? And in any case it does not really answer the question.

My recollection is of calories but I cannot find a source for that right now. Regardless, my point was that if you grow plants to feed to cattle to feed to humans you are taking more resources than if you grow plants to feed to humans. However, it is complex - it depends a lot on the landscape.

http://www.economist.com/blogs/feastandfamine/2013/12/livest...

You also can't ignore the energy cost of running the farm and transportation.

I suspect that it may actually be more efficient to skip pesticide applications and harvesters, and use domesticated insects to harvest grains and fly those food calories directly to a local processing facility.

Certain species are already natural grain harvesting machines. Certain species are already natural pest predators. Those could be exploited and bred for a purpose. Humans plant the corn. Domesticated insect-predator insects patrol the fields and protect the corn from unauthorized eating before it is ready to harvest. They return to the hive, breed for the next season, and get eaten. Domesticated harvester insects then mature, fly out to eat the corn, and then fly back to the hive, breed for the next season, and get eaten.

Whatever is not eaten directly by humans can be fed to farmed fish or poultry.

One calorie of vegetables is a lot less carbon-intensive to produce than a calorie of meat.

As for meat replacement alternatives to help people adjust to a diet with less/no meat: Plant-based meat substitutes (these have become a lot better in recent years), in vitro meat production (still a few years off), or just more beans/lentils in the diet to replace the lost protein.

let them eat cake!

Seriously though - I suspect the majority of american calories already comes from a grass (corn & derived products)