Healthy Eating: What to Do About Meat and Dairy?

As populations grow and incomes rise, we are eating more and more meat and dairy. Intensive livestock farming, however, requires huge amounts of resources and is highly polluting. Yet, animal protein is essential to the 1.3 billion people who depend on livestock to survive. So, what is the solution? To forego animal protein? Eat less of it? Or get it from sustainable and ethical sources?