A good portion of that excess weight is caused by parts of the plant that we, as humans, can not digest either (cell walls, exceptionally long carbohydrate chains, etc). So while inefficient, us humans wouldn't get much more nutrition out of those 8 lbs of grains.

Also, it's worth remembering that we get a lot more than just meat out of your average cow. We get medicines, leather, meat, fertilizer, gelatin, and pet feed. In fact, the ~40% of the cow which is left after butchering is rendered down into a streams of protein and fat for secondary uses, resulting in zero waste of the animal.

There are simply a lot of things you use day to day which come from those cows and those 8 lbs of grain...

You aren't looking at the whole picture.

http://opinionator.blogs.nytimes.com/2012/05/15/we-could-be-...

>It takes 100 times more water (up to 2,500 gallons) to produce a pound of grain-fed beef than it does to produce a pound of wheat. We’re also running out of land: somewhere around 45 percent of the world’s land is either directly or indirectly involved in livestock production

http://www.scientificamerican.com/article/the-greenhouse-ham...

>the meat [in our diets] cause more greenhouse gases carbon dioxide (CO2), methane, nitrous oxide, and the like to spew into the atmosphere than either transportation or industry.

http://www.nytimes.com/2008/01/27/weekinreview/27bittman.htm...

>Global demand for meat has multiplied in recent years, encouraged by growing affluence and nourished by the proliferation of huge, confined animal feeding operations. These assembly-line meat factories consume enormous amounts of energy, pollute water supplies, generate significant greenhouse gases and require ever-increasing amounts of corn, soy and other grains, a dependency that has led to the destruction of vast swaths of the world’s tropical rain forests.

>Just this week, the president of Brazil announced emergency measures to halt the burning and cutting of the country’s rain forests for crop and grazing land. In the last five months alone, the government says, 1,250 square miles were lost.

That's true, but on the other hand you get a much bigger nutritional boost out of eating the beef - it's rich in protein and other things that we need to live, which can't simply be replaced with more carbs. I'm not a big consumer of beef and I agree with your general point, but it's not the 1:1 equivalence which would mean 7/8ths of the beef someone consumes is a waste.

I do not eat meat and I do not have to eat more food than I did when I did eat meat. You've made a statement of fact, but it's at best highly ambiguous, but probably just outright false. You're confusing a bunch of nutritional concepts and coming to a non-sequitur conclusion.

That's not what I meant at all - there are plenty of other non-meat sources of protein, from cheese to nuts, depending on how vegan you are. Once again, what I'm taking issue with is the notion that because 8 units of grain are needed to provide 1 unit of beef, the units are nutritionally identical. Making weight for weight comparisons as above is what's a non-sequitur.

Getting such comparisons fully correct is certainly hard, but I don't think it goes the way you think it does in this case... looking at a few different specific possibilities for "beef" and "grain", the "grain" looks to usually be nearly twice the calories of the "beef" per pound. Humans do not actually need huge amounts of protein and there is rarely a (medical) need to go out of your way to get protein no matter what your diet is.