You may head to the supermarket with the best of intentions—all organic, baby!—but if your junk food-loving partner tags along, you may find yourself caving to the cookies. It’s not that you’re weak: In relationships, the partner with the least self-control influences joint decisions the most, according to a new study in the Journal of Consumer Research.
You might think that all of your decisions are entirely yours, but the truth is, choices where self-control factors in are heavily influenced by the people around us, the study authors say. Think about it: When your coworkers are ordering takeout, are you swayed by what they’re eating? Do your boyfriend’s vacation preferences influence yours? These types of scenarios are what the researchers call “joint self-control decisions.â€
In their first study, the scientists gauged 74 people’s level of self-control, then paired them off into three types of couples: one person with high self-control and one with low, two people with high self-control, or two with low self-control. The duos were then asked to agree upon one meal off of a menu, which included nutritional information—keeping in mind that they’d pledged to stay in shape this summer.
A surprising trend emerged: If there was a low self-control individual involved in the decision making, the couples tended to choose significantly fattier dishes—even when there was a high self-control person participating.
MORE: Up Your Self-Control ASAP
In other words, if your significant other usually gives in to temptation and you’re a very regimented eater, he may be more likely to influence your eating than vice-versa. Why? It may be easier to indulge than to try to sway him to eat healthily.
To test whether this is true in long-term relationships, the researchers surveyed married couples about their fast-food consumption and spending/saving habits. Yet again, the low self-control partner dominated the decision-making—couples with at least one spouse with poor restraint tended to eat fast food more often, save less money, and have more credit card debt.  A follow-up study showed that when couples considered booking a luxurious vacation, those where one or both partners had low self-control were willing to shell out 1.3 times more money for the trip than couples where both were high in self-control.
MORE: How To NOT Gain Weight When Your Partner Eats Crap
What this suggests: When it comes to weight loss, the buddy system may lead to “suboptimal results†if your partner doesn’t have as much willpower as you, the scientists say. But there is a way to steel yourself against your S.O.’s influence: Simply remind yourself that it’s important to stand your ground—your health is at stake! In the study, this strategy helped people with high self-control hold more sway over joint decisions.Â
MORE: The Pros and Cons of Working Out with a Friend