An average guy, supposing he weighs about 150 pounds, burns closer to 3.5 calories per minute having sex. The authors write, “Given that the average bout of sexual activity lasts about 6 minutes, a man in his early-to-mid-30s might expend approximately 21 kcal during sexual intercourse. Of course, he would have spent roughly one third that amount of energy just watching television, so the incremental benefit of one bout of sexual activity with respect to energy expended is plausibly on the order of 14 kcal” (emphasis added).
So there you have it. Sex is better for you than watching Downton Abbey…but only by 14 calories.