Sex instead of starvation? Yes, please. Women who have the most sex tend to have smaller waists and hips than those who do the horizontal mambo less frequently, according to a German study. Higher levels of body fat are associated with less brain dopamine activity and overeating tends to increase mood-altering levels of serotonin, both of which can impair sexual desire and/or function, says Stuart Brody, PhD, who reviewed the research. At the very least, a vigorous roll in the hay can burn about 50 calories, so go ahead and have that extra chocolate kiss.