Sex is a great green way to lose weight. In fact, the average sex session burns 150 to 250 calories per half hour—depending on how athletic your sex tends to be. Dr. Laura Berman, PhD, LCSW, a clinical assistant professor of obstetrics-gynecology and psychiatry at the Feinberg School of Medicine of Northwestern University in Chicago, and director of the Berman Center has said that sex is definitely a good workout—even if you aren't extremely acrobatic, as sex naturally gets your heart rate up, which in turn improves circulation and burns calories and fat. By practicing positions other than just missionary, you are also engaging different muscle groups, so it can be both a cardio and toning exercise. The best thing about it (well maybe not the best, but?) is that it's green. There is absolutely no energy or equipment necessary—except your own.