Married people are twice as likely to become obese than their single counterparts, scientists claim.
Greek researchers found that married couples were more likely to become fat due to their significantly changed lifestyle as they "let themselves go".
Married men are three times as likely to suffer obesity while married women are twice as likely to have weight problems, it found.
The research, based on the study of more than 17,000 couples aged between 20 and 70, found that married couples exercised less frequently, had less sex, had poor nutrition and were "comfortable" in their lives.
Married couples spend more time eating together, sit in front of the TV more and often order takeaway ready meals while exercising less.
Scientists from Salonica and Ioannina Universities, who presented their research on Friday to the Panhellenic Medical Conference, in Athens, concluded that "abdominal obesity, or belly fat" was the worst problem among married people.
Prof Dimitris Kiortsis, one of the study's co-authors, said that obesity was found to be directly related to a change in lifestyle.
Prof Kiortsis, from Ioannina University who is also president of the Hellenic Medical Association for Obesity, said most married couples also have less sex, which is considered intense exercise that burns calories.
He said that unmarried individuals originally spend a lot of time keeping fit and making themselves attractive in order to find a partner "but once they get married they let themselves go".
"The need to hunt for a partner is reduced," he said.
"Stress and anxiety is reduced in a good marriage, there is less smoking, and therefore one's appetite increases."
The study advised married couples to take up more exercise, to have only one home-cooked meal a day, to avoid snacks, and to follow a Mediterranean diet which includes a lot of fruit, vegetables and olive oil.