People try, people fail — over and over again. In our efforts to adopt healthier lifestyles, drop extra pounds and get in shape, we try to go it alone, ignoring the most powerful tool many of us have at our disposal: a spouse or significant other.

As co-directors of the Relationship Institute at UCLA, psychology professors Thomas Bradbury and Benjamin Karney M.A. ’92, Ph.D. ’97 have recorded the interactions of nearly 2,000 volunteer couples over the last two decades to glean insights into how partners communicate, for better or worse. When these couples are asked what they would like to change, the majority — as many as 70 percent — express a desire to become healthier and more fit. The problem is that as much as they’d like to support a partner’s ambition to change his or her diet and exercise habits, most people don’t know how to do that — or they go about it the wrong way.

For many, Bradbury notes, talking with a partner about eating and weight loss can feel like tiptoeing through an emotional minefield. “To our surprise, these turn out to be very difficult conversations,” Karney says. “We study newlyweds who are deeply in love, and yet they have trouble navigating these issues without falling into what we recognize to be common traps that take them off course.”

In their 2014 book Love Me Slender: How Smart Couples Team Up to Lose Weight, Exercise More, and Stay Healthy Together, Bradbury and Karney outline pitfalls to avoid, as well as strategies partners can implement to help each other achieve their goals.

I Love You Just the Way You Want to Be

The interaction of one couple recorded by the UCLA professors presents a classic conundrum. “The wife says to the husband, ‘I think I’m getting too heavy and might need to do something about it. What do you think?’” Karney recounts. “And you could see the panic in the husband’s eyes as he went through his options and discarded them: If I dismiss her, I’m invalidating her concerns. If I agree with her, I’m saying she’s unattractive.” In fact, Karney and Bradbury note, while a well-intentioned partner might be inclined to offer assurance along the lines of “I think you’re perfect just the way you are,” that doesn’t indicate a willingness to support the partner’s desire to become healthier and is likely to foster complacency. A better response: “It doesn’t matter what I think. I love you either way, and if you want to make a change, I will support you.”

Do as I Do, Not as I Say

On the other end of the spectrum, what do you say to a partner who seems unmotivated to make the lifestyle changes you think he or she should undertake to get healthier?

In general, it’s best to stay mum. “If you say, ‘I think you need to lose weight,’ that might be seen as a profound rejection that leads to resistance,” says Bradbury. What you can do is model healthful behaviors and invite your partner to join you, even if the invitation is nonverbal. For example, when you stock the fridge with nonfat yogurt for yourself, it’s easier for your partner to partake. When you make regular trips to the gym, your partner might be more inclined to go as well. “The difference between a demand and an invitation,” says Karney, “is that a demand reduces your autonomy, while an invitation gives you choices.”

Tempt Me Not

Our ability to eat right and exercise regularly is profoundly affected by our environment. If you do the shopping and fill the pantry with healthful foods, your partner will be more likely to choose those. Avoid introducing unnecessary temptations by, say, leaving leftover pizza in the refrigerator. How about if the two of you are out to dinner and you have the urge to satiate your sweet tooth by ordering dessert? Even if you’re not the one who needs to watch what you eat, wait until you’re not with someone who is fighting that very urge.

Think Small

One common mistake well-meaning partners make is to present the lifestyle changes in grand terms, making the journey sound too daunting. “They’ll say, ‘Start running a mile, and then add a half-mile every week. In no time you’ll be running a marathon,’ or ‘OK, we’re starting over, I’m cleaning everything out of the pantry,’” Bradbury says. People respond much better to small changes than to sweeping, dramatic ones. “I stopped putting peanut butter on your toast — is that OK?” “I hear this low-fat dressing is good — do you want to try it?” “I’m going for a walk. Would you like to come?” Explains Bradbury: “It’s about going beneath the radar, below the defenses, so that you’re not incurring your partner’s resistance.”

Don’t Assume

Avoid making assumptions about the extent to which your partner is looking to change. “People who love each other want to solve each other’s problems,” Karney says. “The problem is that in my rush to solve a problem, I can sometimes skip the important step of understanding what that problem is from my partner’s perspective.” Find out your partner’s goals before offering to help, and allow your partner to articulate the solution so that he or she owns it and is therefore more likely to stick to the plan.

Keep It Positive

It’s common for someone attempting to make significant lifestyle changes to fall off the wagon at some point. How can you respond in a way that increases the likelihood that any setback is only temporary? For one, don’t be negative. “No one enjoys criticism,” says Bradbury. If you’re dismayed to hear your partner ordering one of the higher-calorie items on the menu, bite your tongue and simply go back to modeling by choosing the chicken salad, or try putting a positive spin on things. Instead of “We screwed up tonight by ordering cake,” Bradbury suggests, try something like, “Yes, let’s reward ourselves for the good work, and then tomorrow we can go back to eating healthier again.”

Eyes on the Prize

In the moment, the lure of the cheesecake that sits in front of us feels inexorable — until we stop thinking in the moment. Our partners can help with that. “The couples who are most successful help each other stay focused on the long term,” Karney says. “They unite around a shared commitment to growing old together and being able to enjoy active lives.”