I do believe that, to a point, he is correct in saying that the human body is not as efficient as a combustion engine. If you look at joules of energy put in vs. joules output, an engine is at best 35% effiicient, whereas the human body is a good bit less. However, what he didn't figure in was the amount of energy which goes to powering cognitive ability, sight, hearing, and all the other things which were running, anyways. Come to think of it, a combustion engine needs a human to operate it (unless you are using it as a pump, generator, or some other industrial usage), so that lowers the efficiency of the operating system considerably!
Of course, this nut never seems to realise that the waste products of a combustion engine are much worse than those of any animal.
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Je vais à vélo, donc je suis!