We've all heard that going vegetarian is better for the environment. But how much better, exactly? In the chart below, from The Oil Drum, you can see the energy cost to produce different kinds of food, and then the efficiency of those foods based on the calories they provide.The moral of the story is that the efficiency of different foods varies widely. And while animal products tend to be lower efficiency foods, it's really more that beef is an outlier. Beef is nearly 20 times as costly, in energy terms, as apples. And it's more than twice as costly as pork. Dairy products, on the other hand, are actually pretty efficient because they're high-calorie. And chicken is as efficient as apples.On the opposite end of the spectrum, corn is another outlier. It is far and away the most efficient of these foods. It's no wonder corn is in everything we eat. I wonder where potatoes would rank. I imagine they'd be really efficient too.Ultimately, though, it's also the case that "food production and consumption amounts to only about 10% of first-world energy consumption." So if you're just trying to make the lifestyle changes that will lighten your footprint, try changing your habits as they relate to transportation, heating, and air conditioning.UPDATE: Praveen Ghanta did the analysis in the chart, and it was originally posted on his True Cost blog (which looks fascinating, by the way).