[matthewaustin]

I disagree with your claim that veganism and vegetarianism can't be backed by logical thinking. Producing meat requires significantly more natural resources (land area, water) and produces significantly more pollution (methane, ground contamination) than producing fruits and vegetables.

Here is an example comparing the amount of water needed to irrigate various crops compared to the amount needed to raise beef.

US Corn Production: 9 gallons water / lb corn

US Wheat Production: 14 gallons water / lb wheat

US Barley Production: 26 gallons water / lb barley

US Alfalfa Production: 31 gallons water / lb alfalfa

US Beef Production: 441 gallons water / lb beef

http://www.journalofanimalscience.org/content/71/4/818.full....

Global Spinach Production: 2 gallons water / lb spinach

Global Potato Production: 4 gallons water / lb potatos

Global Banana Production: 13 gallons water / lb bananas

Global Apple Production: 18 gallons water / lb apples

Global Lentil Production: 64 gallons water / lb lentils

Global Cashew Production: 121 gallons water / lb cashews

Global Almond Production: 252 gallons water / lb almonds

http://www.waterfootprint.org/Reports/Mekonnen-Hoekstra-2011...

I could look for more examples, but this took me about half an hour already, and I think it pains a rather compelling picture by itself. The difference would be less extreme when looking at pork and poultry, but there is still a stark contrast.

[jpwagner]

You need to normalize to nutritional value rather than weight.

But the whole point of this thread seems to be that such an analysis is hard to do.

[pron]

Exactly.

There are so many confounding variables here that it's really hard to tell. Everyone pretty much chooses to believe whatever data they like best. For example, cultivated land is probably less environmentally friendly than pasture land.

[matthewaustin]

It wouldn't matter how environmentally unfriendly it was to cultivate land as long as livestock are fed cultivated crops, since they require more than one pound of food to produce one pound of meat.

If x = environmental impact of cultivating crops

then R*x = environmental impact of raising livestock

where R = pounds of feed required to produce one pound of meat

Now if we raised our meat differently, such as only on grass-fed pastures, then things might look a lot different. But in the US at least, factory farming and animal feed is the norm.

[pron]

I'm not too fond of factory farming, but that has little to do with veganism. In any case, your math would be correct only if 1 pound of vegetables consumed by a person is the same as one pound of meat. I guess even vegetarians would admit that's wrong (I think humanoids started eating meat because it was the only thing providing enough concentrated nutrition to support a massive brain, at least without eating all day long).

Moreover, it's quite conceivable (again, no proof, but there's little proof af anything in this field) that herbivores would convert one pound of corn much more efficiently than we would. This might mean that humans are better off wasting energy by feeding vegetables to animals and then eating the animals, than eating the vegetables directly. Maybe we can't extract the nutrients from the vegetables as well as herbivores do, so that seemingly wasted energy is actually a net gain.

[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?

[matthewaustin]

You could measure by calories, since there will not be a huge difference in the number of calories consumed by people with different diets.

Giving an incredibly quick example, wheat and ground beef have roughly the same caloric density

Wheat: http://www.fatsecret.com/calories-nutrition/usda/whole-grain...

Beef: http://www.fatsecret.com/calories-nutrition/usda/ground-beef...

But since it requires numerous pounds of wheat to create one pound of beef, you are losing overall caloric density.

[itsybitsycoder]

I can easily eat a 1/2 lb steak for dinner and feel fine, but eating 8 slices of bread at once will make me feel very sick. so I don't think caloric density is the be all and end all of nutritional value. I mean, wheat and beef also have about the same caloric density as gummi bears...

http://www.fatsecret.com/calories-nutrition/kroger/gummi-bea... https://www.google.ca/search?q=40g*11.3+to+lb https://www.google.ca/search?q=140*11.3