So on the bulletproof executive forums someone had mentioned something about sustainability of grain fed animals for food... well I decided to do some math on the sustainability of just the beef portion of the Bulletproof Diet. (12/16/2016 note - Let me note, while I keep mentioning the Bulletproof Diet, this post is really just about the sustainability of grass fed beef, when I originally wrote this in 2013 I was on a BP Diet kick.)
The Earth only has 7.68 billion acres of arable land, something like 1.4bn of this is forest so we are going to exclude them. so 5.48bn acres. Wiki lists the largest 153 cities listed by area in the U.S. using whole numbers only that's 89,874 square miles or 57,519,360 acres, lets multiply this by 1.5 to account for interstates and smaller cities/towns/etc and then by 5 for the 5 inhabited continents... that leaves us with 5.04 billion acres.
In the United States, a single cow during warm seasons needs anywhere from 2-25 acres of arable land (actually, in parts of the world this number could be higher but lets make this easy) to feed on (depending on the region, most of central Indiana 2 acres is good, say in the Dakotas 25 acres of unimproved prairie is needed).
Let's average this, 13.5 acres per cow, lets be extra generous and slash that in half, 6.75 acres, now lets be generous again and assume only 3.25 acres more used only for saving grass for the cold season. 10 acres per cow per year.
It takes about 2 years for a cow to reach slaughter weight. The average grass fed cow will yield about 530lbs of meat. Assume 1lb consumed per day per human.
The Earth had a population of 6.974 in 2011. That's 6.974 billion pounds of meat a day for the BP diet.
You need 5.091 TRILLION pounds of beef every 2 years for the world to eat BP diet at 1lb a day per person. With the Earth at 5.04bn acres arable for us to use you can feed 252 million cattle to slaughter weight. Every 2 years you can produce 133.56 billion pounds of beef assuming no deaths.
Ought oh!!! Bulletproof diet isn't sustainable either! Even if you drop it to 1/4lb per day per human that's 1.27275 TRILLION pounds of beef needed every 2 years while you can produce 133.56 billion pounds... that's still nearly 10x what you can produce.