Serious about toning up and losing weight in 2017? Your biggest challenge might not be the drive to the gym or lack of time — but the spouse who is happy eating junk food and vegging out in front of the TV.

When couples agree on a lifestyle, there’s a mutual bond and perspective on life. But when one partner seeks to make positive change and the other is not interested, it can challenge the success of the goal and the relationship.

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Partners Influence Each Other
Not only do partners wish to please each other, they also want to live harmoniously. This can mean not speaking up for themselves — or caving in to pressure to join their spouse in unhealthy habits.

It’s not unusual for couples to have very different outlooks on food, alcohol, exercise, and downtime, according to Jonathan Bennett, a certified counselor and dating/relationship coach in Columbus, Ohio. And it can be tough for couples to see these differences in the early part of a relationship.

Positive habits can slowly erode in the face of poor habits.

“As people fall in love, they tend to see the only the best in the other person,” Bennett told LifeZette. “It’s called the halo effect. So unhealthy habits might be seen as quirks or outright ignored, rather than viewed as possibly destructive in the beginning.”

It’s also common for one partner to believe the other will change after marriage or cohabitation, but that may be the last thing on that partner’s mind. Instead, that person might ease up on any emphasis on their appearance, since he or she is out of the dating scene.

Sabotage Is So Common
Positive habits slowly erode in the face of poor habits, said Bennett. It doesn’t happen overnight, and it can be a shock when one partner realizes he or she has let his health go (or the partner has). Often, this can disrupt a relationship.

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“One partner can sometimes feel threatened if the other starts developing better habits,” Bennett explained. “If one person gets clean from alcohol, loses weight, or betters himself or herself, the other might feel inadequate or jealous. In that case, the partner stuck in bad habits may try to sabotage the other. For example, a person trying to improve might hear comments like, ‘One cheeseburger won’t kill you,’ or, ‘Since you stopped drinking, you’ve been boring.'”

Resentment often builds in these situations, said clinical psychologist and behaviorist Dr. Jennifer Guttman of New York City.

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“I believe it’s possible to stay together, but it’s difficult if they have different levels of health,” Bennett explained. “You see this with addicts. It’s very common for the unhealthy partner to drag the recovering one into relapse, rather than the other way around. Usually, they both need to stop the behaviors or split up, for one or both to have any success.”

Time for Professional Help?
If a couple stays together even though they have different health habits, a bigger structure has to bind them. Exploring the topic with a qualified professional before marriage can help both parties plan for how they will deal with the challenges of differing lifestyles.

It took Ken and Emme Buford, of Milwaukee, Wisconsin, several tries to get healthier.

“Invariably, he would drop weight so much faster than me,” Emme Buford said. “He got so many positive comments, I couldn’t stand it. It always led to me sabotaging myself, because I couldn’t keep up with his pace, and felt I wasn’t doing it right. He would then feel bad and then join me in the descent back to bad habits.”

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The couple finally met with a coach and set some ground rules about how they spoke to each other, and how they supported each other, no matter what friends said or didn’t say.

“I realized he hit plateaus differently, and struggled with other issues about losing weight and being more fit,” Emme Buford said. “We had to learn what to share and what to keep private. We had to learn to keep our eye on the goal, not the missteps along the way.”

Pat Barone, MCC, is a professional credentialed coach and author of the Own Every Bite! bodycentric re-education program for mindful and intuitive eating, who helps clients heal food addictions.