Couples who live together are more than twice as likely to become obese than those who live separately
The study to be published next month in the journal Obesity also showed that the risk of obesity rises the longer people live together.
Penny Gordon-Larsen, associate professor of nutrition at the University of North Carolina, found some positive health benefits to marriage, including decreased cigarette smoking and lower mortality.
But she added: “We also see greater weight gain than in others of the same age, and greater risk of obesity.
“Maybe the cause of weight gain is not just age, but the pressure of shifting behaviours that result in weight gain.”
She said people living together – married or not – tended to eat meals together, possibly cooking bigger meals or eating out more often than they did when they were single.
They were more likely to watch television together instead of going to the gym or playing a sport. Her research found that couples who lived together for more than two years – especially those who were married – were most likely to display similar obesity patterns and physical behaviours.
She added: “Maybe this a good time to intervene with these young couples and get them to have a more positive effect on each other.
“Couples can use that phenomenon to their advantage if they’re aware of what’s going on.” “They can be good influences on each other. That may be how they can avoid the extra pounds now associated with marriage.”