We've all had that friend who disappears for a month, only to emerge newly coupled and minus ten pounds. Or the friend who gets hitched and then develops a belly. What appears to be an individual phenomenon is actually deep seated in our social and psychological behavior. Food and love are inexorably linked, thanks to a complex hormonal reaction that affects our emotional attachments to loved ones -- and our need for food.

Notably, early in the relationship, eating takes on weighted significance, according to Maryanne Fisher, a professor of psychology St. Mary's University in Halifax, Nova Scotia, whose research focuses on the evolutionary basis of romantic behavior. "Food is a way to display skills to a potential mate," Fisher told HuffPost Healthy Living. "You might buy nicer food, prepare better meals. It's fascinating how it can be used as part of the relationship."

If the food is a display -- say, if one partner cooks food for another, or one buys a fancy dinner for the other -- that's preferable, because those who are newly in love tend not to eat much. As Fisher noted in her essay on the subject, those who are newly infatuated produce an overabundance of "reward hormones" like norepinephrine. Those in turn produce feelings of euphoria, giddiness and energy. But they also suppress appetite in many, according to Fisher.

But as with all things, "love hormones" that go up must come down, and, in extreme cases, that can lead to obesity. One 2008 University of North Carolina, Chapel Hill study found that women who were married were twice as likely to become obese as their peers who were single. Those who were cohabiting, but not married, were 63 percent more likely to become obese than single women. Men didn't emerge unscathed: married men were also twice as likely to grow obese, though cohabiting men were no more likely to be obese than their single counterparts.

For one thing, weight gain includes an element of social contagion. If one spouse has poor eating habits, such as a lack of portion control or a preference for unhealthy foods, that may extend to the other spouse. And, as nutritionist Joy Bauer explained during a segment on TODAY about the subject, there is little motivation to stay away from the cozy snacking:

Most importantly, if you’ve settled down with someone, you’re no longer facing the competition of the dating field. That means you may have less incentive to stay in shape and look your best. Plus, your lifestyle starts to revolve around food a bit more. As a couple, you probably stay in and cozy up (with food) on the couch more often than you did when you were single.

Did you gain weight during the course of a relationship or after marriage? Did you lose weight falling in love? Tell us in the comments!

Photo from amazon.com.

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