Being part of a couple seems to feed weight gain.

RODALE NEWS, EMMAUS, PA—It stands to reason that women gain weight after they have kids. They may not have time to exercise, or they could be overly stressed with the responsibilities of being a new parent. While a new study of a large female population in Australia confirms this fact, it also found that women who get married or move in with their boyfriends are just as prone to packing on the pounds, even if they never have children.

THE DETAILS: The study, published in the American Journal of Preventive Medicine, took place over the course of 10 years, during which 6,458 women completed surveys related to food consumption and calorie burn. The women also reported on their relationship status and whether they had children. The average annual weight gain of all women in the study was 0.93 percent of their body weight, or about 1.3 pounds for a 140-pound woman. Women who had children gained the most weight, an additional nine pounds per year, but women without kids who were married or living with a partner gained a fair amount, too—an additional four pounds per year.

WHAT IT MEANS: Women often blame weight gain on having kids, the authors write, but it appears that the social and lifestyle factors related to living with someone have an impact, as well. "When you get married, it's a change to the routine you have when you're single," says Suzanne Farrell, MS, RD, spokesperson for the American Dietetic Association, "and any type of change can have side effects." The trick to maintaining your singlehood weight throughout your married life and beyond, Farrell says, is realizing how those changes can affect your eating and exercising patterns.

Read on for tips on staying thin after falling in love…