For years we've been hearing about how married people live longer, lead happier lives and are less prone to all manner of medical conditions.  Finally, the singletons get some semblance of revenge, as the latest research shows there is at least one area where married couples lose out. That area just happens to be their waistlines. A study into the body mass index of more than 10,000 people from Austria, France, Germany, Italy, the Netherlands, Poland, Russia, Spain and the United Kingdom found that in all countries BMI was higher for people who were married. Ralph Hertwig, director of the Center for Adaptive Rationality at the Max Planck Institute for Human Development in Berlin, said: “Our findings show how social factors can impact health. “In this case, that the institution of marriage and certain changes in behaviour within that context are directly related to nutrition and body weight.” Don't throw the engagement ring out with the bathwater though - as the average difference was not a big one. The average BMI of single men in the study was 25.7, while married men were 26.3. The average BMI for single women was 25.1 while married women were 25.6. It's still bad news overall, as according to the World Health Organization anyone with a BMI between 25 and 30 is actually overweight.