Not quite, you lose ten percent, but that means the other ninety percent is compressed to a much more smaller amount. If you were to try and eat grass versus cow, you would need only really one tenth as much mass of cow flesh, as you would with grass. In other words, our stomachs have a hard time fitting all that food at once. Sure you may lose energy, but it's more condensed.Comocat said:Meat is an incredibly inefficent way to feed a population. If I remember from ecology you generally transfer approximately 10% of energy between tropic levels. So if you go from Plant --> Cow --> Person, you are losing 99% of the energy the plant had made from the sun. If you consider the economic and environmental consequences of 9 billion people moving to a meat centered diet, suddenly the carrying capacity of the world is a lot smaller. So you can be vegetarian or vegan morally by justifying yourself with physics!
Post Script:
If it was so efficient to just eat the grass, we would've never evolved the carnivore based diet, as it would be just ineffective and rooted out by the more efficient herbivore diet.
Bonus points for noticing semi pun.