[matthewaustin]

Energy is always lost as you move up the food chain, because no predator can capture 100% of the energy stored in their prey.

Consuming plants is not as efficient as photosynthesizing, and consuming animals is not as efficient as consuming plants.

In this case, the cows burn energy from the food they consume for as long as they're alive, meaning it's a physical impossibility for the meat produced from them to contain as much energy as the food they consumed.

Unless you're claiming that raising livestock violates the laws of physics, but that's an entirely different argument.

[itsybitsycoder]

No, he's suggesting that it's possible humans digest plants much less efficiently than herbivores do, and less efficiently than humans digest meat. E.g., if the herbivore can capture 90% of the energy in a plant, and we can capture 80% of the energy in the herbivore, that may be a better deal than if we can only capture 10% of the energy in the plant directly. In the case of cows eating grass, that doesn't sound that far-fetched. They have the benefit of multiple stomachs evolved to break down fibers, and we don't. Surely you don't think that every animal digests plants more efficiently than they digest meat? What about obligate carnivores, which can extract roughly 0% of the energy from plants?