What does " It's a protein factory in reverse." mean? Cattle are born with the ability to convert grasses that we humans cannot digest into flesh that we can digest. They can do this because, unlike humans who possess only one stomach, they are ruminants. They possess a second stomach called a rumen — a roughly forty-five-gallon tank in which resident bacteria convert cellulose into protein and fats. In today's feedyards, however, cows fed corn and other grains are eating food that humans can eat, and they are quite inefficiently converting it into meat. Since it takes anywhere from seven to sixteen pounds of grain to make one pound of beef, we actually get far less food out than we put in. It's a protein factory in reverse. And we do this on a massive scale, while nearly a billion people on our planet do not have enough to eat. What does " It's a protein factory in reverse." mean?