[saalweachter]

"Vegetables" are the wrong thing too look at.

Soybeans have about 2000 calories / lb, based on the number Google gives me of 446 calories / 100g. A random website claims soybeans take 200 gallons of water to produce 1 lb, which comes out to about 10 calories / gallon.

That said, you can make huge gains just by switching from beef to pork or chicken. Pork uses about half the resources of beef, per pound, and chicken about a third. Eat your beefs for special occasions, eat chicken and pork if you want every-day meats.