(View videos of married couples discussing their health and more from Bradbury and Karney.)
After analyzing thousands of hours of video recordings of married couples talking with each other about their health, two UCLA psychology professors were shocked by what they saw. 
The recordings showed hundreds of couples, many of whom wanted to lose weight and get more exercise. Almost all of them were still early in their marriages, so the psychologists assumed their conversations would be warm and affectionate, said Thomas Bradbury, a psychology professor in UCLA's College of Letters and Science who co-directs the Relationship Institute at UCLA.
"That's not what we observed at all," said Benjamin Karney, also a UCLA psychology professor and the co-director of the institute. "Yes, couples were turning to each other for support, but their conversations went awry in more cases than not. The couples struggled to have these conversations, and they were as surprised as we were at how difficult it was."
This revelation led the professors to write "Love Me Slender: How Smart Couples Team Up to Lose Weight, Exercise More, and Stay Healthy Together" (Touchstone/Simon & Schuster), which will be published Feb. 4. In the book, Bradbury and Karney, who have studied close relationships for more than two decades, offer new solutions for couples trying to communicate about the emotionally charged issue of weight loss.
"Even couples who love each other have difficulty doing this effectively," Karney said. "There are skillful ways to talk about physical appearance and attractiveness that may not come naturally to couples; that's why we wrote this book."
Bradbury said couples who succeeded in those conversations provided each other with motivation, encouragement and support. "They said things to each other like, 'I love you and that's not going to change, but I'm going to help you stay healthy and lose weight. We'll work on this together.'"
Less than 10 percent of U.S. adults meet all four criteria for a low-risk lifestyle: not smoking, exercising regularly, maintaining a healthy weight, and eating enough fruits and vegetables. But long commutes, demanding jobs, and caring for children and aging parents are among the many challenges that get in the way of healthy living. 
Fortunately, loved ones can help us maintain healthy habits.
"If we live with our partner, then we share a kitchen with someone else," Bradbury said. "So it makes sense that when one partner goes on a diet, the other partner often loses weight, too."
Similarly, Karney said, when one partner exercises, the other is typically influenced to do so as well. 
Weight and appearance are sensitive subjects for most couples because the topics are directly related to the question of whether partners still find each other attractive — and it can be a challenge to provide emotional support while lovingly and effectively criticizing each other.
"It's a delicate balance," Bradbury said. "If your spouse says, 'You look fantastic the way you are,' the partner can think, 'OK, then I'll stay on the couch and eat more chips.'"
Karney said that can be a difficult line to navigate. "'Are you saying you love me the way I am or that I need to change?' Those seem like contradictory messages."
Citing previous research, the authors said that relationships benefit when both partners are healthy.
"When we exercise more and eat better, our moods improve," Bradbury said. "We manage stress better; the quality of our sleep improves and we are mentally sharper; our sexual performance improves, and we become closer and more content in our relationship. After a while, you no longer think of yourself as being on a diet, and you start to identify yourself as a healthy couple.
"Your partner can be your conscience," he said. "When we're alone, we may be unwilling to make sacrifices, but if we have someone we love who says, 'We can have a great dessert on Saturday, but let's go without a dessert during the week,' we can use the strength both of us have to do the healthy thing. The trick is to do that in a way that respects your partner and is not threatening. It's hard, but important, so why not turn to the person who loves you the most?"
Paradoxically, though, a good relationship can get in the way of couples taking care of themselves. Karney said that one husband in the study simply did not want to exercise without his wife, even when she encouraged him to do so. "His desire for togetherness became an excuse not to do anything at all for his health," he said.
Karney's advice? "When we commit to a relationship or to a marriage, we commit long-term, often for a lifetime," he said. "Borrow a little of that kind of commitment and apply it to your own health and to a diet and exercise plan. The relationship helps us to think of the rewards of being healthy, and not just the ice cream you're not eating." 
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