If you find yourself gaining weight once you’re in a relationship, you’re not alone. A recent study that compared the body mass indexes of singles to spouses found that, on average, coupled people had higher BMIs than people who were single.
Scientists from across Europe analyzed data from over 10,000 people in Austria, France, Germany, Italy, the Netherlands, Poland, Russia, Spain and the U.K. They found that while the average single man had a BMI of 25.7, the average married man had a BMI of 26.3. The average single lady had a BMI of 25.1, while the average married woman had a BMI of 25.6.
For reference, a BMI of 25 or higher is considered overweight; a BMI of 30 or higher is considered obese.
The study doesn’t explain why there are weight differences between married and single people, but lead author Jutta Mata of the University of Basel said that her findings did support what scientists called the “Marriage Market Hypothesis.” That is, once you’ve found a mate and are “off the market,” there’s less incentive for you to invest in your looks by keeping your weight down. For instance, said Mata, in countries with high divorce rates, married people have lower BMIs than married people in countries with a low divorce rate. Perhaps this is because those who live in a high-divorce culture understand that there's a higher chance they’ll return to the “marriage market.”
Counterintuitively, marrieds reported buying more organic and fair trade food, as well as more local and unprocessed food, compared to singles. That means they were probably eating healthier meals or at least eating more consciously than singles, but the better diet didn’t translate into healthier weight, on average.
Part of it may have to do with the fact that husbands reported doing less exercise than single men, Mata said. It could also be because marrieds, on average, said that they paid less attention to the amount of fat in their food as well as their own body weights.
Previous research, most notably a smaller 2013 study, found that the happier a couple was, the more weight spouses gained in the first years of their marriage.
A few extra pounds doesn't mean there's anything unhealthy about marriage. Quite the opposite, in fact: a large body of evidence supports the conclusion that marriage is linked to many health benefits (which makes the Supreme Court’s recent ruling on gay marriage all the more exciting). Happily married people are more likely to live longer, have overall better health, have stronger bones and are less likely to have heart attacks.
Mata advises couples who struggle with their weight to take advantage of the fact that they have someone with whom they can share resources and goals. In most instances, married couples have more resources than single people, which they can use toward a shared goal of healthier habits, she concluded.
CORRECTION: A previous version of this story incorrectly spelled Jutta Mata's last name. We apologize for the error.