Liz Neporent is a diet and fitness expert and author of 12 fitness bestsellers. She regularly appears on national TV programs and is the president of Wellness 360, a New-York based wellness provider.

Have you ever looked at your wedding picture and thought, "There is no way could we fit into that gown and tux anymore,"? You apparently have plenty of company, because women tend to gain weight in the few years following marriage, research suggests, and the typical married man is heavier than single or divorced men of the same age.

Just how many pounds do married people tend to gain after walking down the aisle, and how quickly does the weight pile on? No one knows for sure. Studies have produced very mixed results, and the research methods have been so varied, that it's tough to make generalizations. However, a brand new University of North Carolina study found that newly married women and men tend to gain six to nine pounds shortly after exchanging vows -- almost as if the words "I do" mean "I do like to eat."

Why might married folks be heavier than single people? One theory is that married couples eat more frequently and eat larger portions because they often dine together. Whereas a single person might grab a sandwich while reading a magazine, then move on to the next activity, a married couple might linger at the dinner table, heaping second helpings on their plates. Another theory is that single people may make more of an effort to keep their weight down as part of a strategy to attract a mate; once they've found a spouse, they grab a plate, unbutton their pants and head for the all-you-can-eat buffet. Or perhaps people exercise less after they get married because they're busy with family obligations and other couple stuff.

Whatever the reasons, there is mounting evidence that weight gain is contagious and your spouse isn't the only one you can catch extra pounds from. Your friends, your coworkers and your family also have a huge influence on what dress size you grab off the rack, and this is largely down to social factors rather than genetic ones. The on-going Framingham Study in Massachusetts has found that chances of becoming obese increased 57 percent if a friend also got fat. It went up "only" 40 percent if a sibling became morbidly heavy compared to "only" 37 percent if a spouse did. The odds of becoming obese went up by 71 percent if a same-sex friend gained weight, by 67 percent between sisters and 44 percent between brothers. In some cases, this was true even if individual weight gainers lived thousands of miles apart. This implies it can't all be blamed on similar exercise and eating habits but rather similar attitudes and levels of acceptance of weight gain, e.g., you may not be so bothered about being fat if your best friend or your sister is also a heavyweight.

So does this mean you should get divorced, quit work and go live in a cave if you want to remain thin? (And for that matter, you may want to disown your parents early on since there is plenty of data to show how strongly they influence your weight, eating habits and exercise patterns before you are even out of diapers.) Maybe a better strategy would be to gather up everyone in your "Fav Five" and head straight to the nearest gym or weight loss center so you all can make your lifestyle changes en mass. Or perhaps you could simply become more aware of how strongly your weight is influenced by those you love so you can make a conscious effort to be healthy no matter what those around you do, say or think.

What has your experience been with contagious weight gain? Have you caught any sympathy pounds sneaking under your belt when someone close to you has gained weight? Or, have you been motivated to muscle up when a friend set a good example? Would love some real life examples of this phenomenon to share with the group.