Apparently a new study just published in the New England Journal of Medicine, sex only burns up 21 calories. Of course they based that on a time of six minutes for sex. The study conducted at the University of Alabama also concluded that many other long-held beliefs were in fact myths.
http://news.yahoo.com/blogs/sideshow...224521651.html
http://www.cbsnews.com/8301-204_162-...y-researchers/