This a tangent, but on another website I read a comment which made me wonder about the efficiency of car fuel vs human fuel. I wouldn't know how to begin to figure this out, but it's worth thinking about.

Does also the production, distribution and preparation of x human energy food calories burn less than x gallons of gas?”

There is so much oil embodied in food production and distribution, that on certain assumptions bicycles have a mpg consumption which is no better than a car.