Buried in an article reviewing the myths and facts of obesity and weight-loss in this week’s New England Journal of Medicine is this gem:

“Myth number 7: A bout of sexual activity burns 100 to 300 kcal for each participant.”

There’s no shortage of Web sites extolling the cardiovascular virtues of sex, from undressing to foreplay to intercourse. Suffice it to say that they’re long on pseudo-science and short on data. A random sample:

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WebMD estimates that 30 minutes of sex can burn 85 calories or more. “It may not sound like much, but it adds up: 42 half-hour sessions will burn 3,570 calories, more than enough to lose a pound.”

HowAboutWe is slightly more enthusiastic. Unclasp a bra with your mouth? Sixty-seven calories. Make love standing up? Six hundred calories.

Gizmodo puts a Nike Fuelband to the test and reports that intercourse burned 179 calories—six times more than washing the dishes.

Livestrong argues that “in terms of calories burned, foreplay is roughly equivalent to an hour of watering the lawn while sex is equivalent to raking the lawn.” Even so, the site cautions, “You should not rely on sex as your only form of exercise.”

Woman’s Day, meanwhile, says that “the key for high-calorie-burning sex is making it hot and making it last.” Jaiya Kinzbach, an L.A.–based “sexologist,” adds that “a little moaning and sighing” can burn an extra 18 to 30 calories.And while you’re at it, why not mix in a few “calorie-blasting” pushups and yoga poses?

The New England Journal’s rather more sober assessment? 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.