You've had a rotten day and all you can think about is curling up on the couch with [insert your favorite comfort food here]. What gives some foods the power to soothe? "Stress causes most people to want to eat, period," says David LaPorte, Ph.D., an associate professor at Indiana University of Pennsylvania who specializes in the psychology of eating disorders. "That's just built into our brains as mammals. If you put a paper clip on a rat's tail, the first thing it will want to do is eat. Also, food is extremely rewarding to the brain. Just the act of eating lights up the lateral…