It is estimated that 2 billion people live primarily on a meat based diet,
while an estimated 4 billion live primarily on a plant-based diet.

In the United States, we currently use about half of the total land area
for food production. We also use about 80% of the fresh water for food production as well as 17% of our fossil consumption to produce food. Producing animal proteins will be more expensive and put a greater stress on our environment due to the animal waste disposal

As we go into the future and our population grows, this formula is not
sustainable. Meat based diets will fade. We will become more dependent on plants, both from the land and the sea for our food supply.

http://foodmatters.tv/articles-1/top-6-plant-based-proteins