Meat

"If pigs are fed on residues and waste, and cattle on straw, stovers and grass from fallows and rangelands – food for which humans don't compete – meat becomes a very efficient means of food production. Even though it is tilted by the profligate use of grain in rich countries, the global average conversion ratio of useful plant food to useful meat is not the 5:1 or 10:1 cited by almost everyone, but less than 2:1. If we stopped feeding edible grain to animals, we could still produce around half the current global meat supply with no loss to human nutrition: in fact it's a significant net gain."

From an article in the guardian on the book "Meat: A Benign Extravagance" by Simone Fairlie