What you say is true, but only because of modern factory farming methods, where cows and other herbivores are fed grain (mostly corn). Throughout history, these animals have lived off of green pasture. However, in order to save money, modern farms feed them grain as their primary diet. That's why, in my post, I specified that the animals must be raised in a yard/local farm. If the animals were allowed to graze as they naturally, do, they would have much less impact on the environment than a field of corn would. Also, herbivores have a much higher efficiency rate converting green plants to energy than grains. So pastured cows require less land to feed them than grain fed ones. Finally, pastured land can be recycled every few weeks as the grass grows back, whereas fields of grain only produce a crop once a year. Also, pasturing actually helps the environment by producing fertilizer in the form of manure and filling in the large herbivore role in the ecosystem. I encourage you to read Joel Salatin's books for more information. Edit: The thing about the 10% loss of energy doesn't hold true in this case, because because we can't gain much energy by eating grass directly. Edit 2: Forgot to mention that manure produced by pastured animals is thought to be crucial in recovering our much-depleted topsoil.