Every time we eat meat, it's as though we're throwing away 6-20 calories worth of grains and legumes for every calorie we take in.
And that's just the pure "calories in, calories out" equation. When you factor in all the extra stages of production that are required for meat relative to grains and legumes, the anti-environmental nature of meat consumption becomes even more stark: First, you have to grow many times more corn, grain, and soy (with all the required tilling, irrigation, crop dusters, poisons, and so on), than would be required if we ate the plants directly. Then you have to transport all that grain and soy to feed manufacturers, in gas-guzzling, pollution-spewing 18-wheelers. Then you have to operate the feed mill (again, using massive amounts of resources), truck the feed to the factory farms, operate the factory farms, truck the animals many miles to slaughterhouses, operate the slaughterhouses, truck the meat to processing plants, operate the meat processing plants, truck the meat to grocery stores (in refrigerated trucks), and keep the meat in refrigerators or freezers at the stores.