Obesity is spreading like a virus -- literally. According to recent analyses of thousands of participants over three decades, you're more likely to get fat if your friends do. Looking at obesity as a sort of social contagion may even help explain why the weight of America's residents has suddenly ballooned over the last generation.

Sound farfetched? Well, not according to Nicholas A. Christakis, physician and professor of medical sociology at Harvard Medical School, and a principal investigator of a study published in the New England Journal of Medicine that tracked a large social network of 12,067 people between 1971 and 2003. Unlike most studies of its kind, which only record the relationship of an individual and his/her contacts, the Framingham Heart Study looked at a network, practically tracking the entire town of Framingham, Massachusetts, and each participant's social contacts.

Studies like this could be especially important to Texas, where obesity has become a major health problem. Sixty-one percent of adults and 35% of children in the state are considered obese, and it's not just a cosmetic problem. The condition is a serious medical issue, and can lead to heart disease, type 2 diabetes (also at epidemic levels in Texas), stroke, and even certain cancers. In a state where 25% of the population is going without health insurance, and the health care systems are already overburdened -- particularly in the larger cities of Dallas, Houston, and Austin, where rural residents come seeking care -- any increase in disease could effectively collapse the system.

The Framingham study was actually a large federal study intended to investigate heart disease. Every four years, each subject was examined and asked to name at least one person who would know where he or she would be at the time of the next evaluation. As most of the town and its relatives participated in some fashion, a large social network was tracked and data, such as weight and body mass index, recorded. Investigators knew each participants' relationships with each other -- be it sibling, spouse, neighbor, or close friend.

Analysts concluded that an individual was 57% more likely to become obese when a close friend did. In fact, friends had more influence on each other than family. Statistically, there was no effect when neighbors gained weight, and close mutual friends had the most affect on each other, even if they were hundreds of miles apart. If one became obese, the other had a 171% chance of following suit. The same effect was noticed for weight loss, but as Americans have been predominantly growing fatter, an increase in weight was seen more often.

If the idea of likening obesity to a contagious disease seems harsh, perhaps it is, and, according to Christakis, he and colleagues are not intending to blame the patient for the disease so much as to determine why the epidemic is occurring. One explanation for the dramatic increase in American poundage is that an obese person is likely to influence another in his or her social network (i.e., a friend) to also become obese, in the same way that an individual losing weight might. Friends may also affect each other's perception of fatness, and what weight is acceptable. "[the effects] highlight the importance of a spreading process, a kind of social contagion, that spreads through the network," said Christakis.

While Richard M. Suzman, from the National Institute on Aging (which funded the study) hails it as "one of the most exciting studies to come out of medical sociology in decades," colleagues like Kelly D. Brownell, director of the Rudd Center for Food Policy and Obesity at Yale University, aren't so sure. "I think there's a great risk here in blaming obese people even more for things that are caused by a terrible environment," said Brownell.

Further, no one disputes the influence genetics have on the condition. An individual generally has a genetically predetermined weight range, usually around thirty pounds. The environment, then, can play a major role in determining whether a person is near the bottom or top of that range. With all the advertisements for heavily processed, sugary, and high-fat foods that are cheaper than healthier produce, it's easy to see how "environment" can be a negative influence, indeed.

The Framingham review is unique, which can be seen as a rare and tremendous breakthrough, as well as a study that's difficult to replicate -- an important aspect in determining its overall scientific validity -- according to Stephen O'Rahilly, an obesity researcher at the University of Cambridge. No other study has the same, long-term, detailed analysis of a population and its social networks, and it could take another thirty-two years to produce one. Its results are telling, and something to consider. How much do we influence each other, and not realize it? If we can encourage our friends to gain weight simply through our own attitudes and habits, then can we, instead, encourage them to be healthier? Viewing the results as an opportunity to be aware of how much we can influence each other to do better, or as just highlighting another factor working against us, is really a matter of perception.

Keeping your weight at a healthy level is an important aspect of taking care of yourself. How you take care of yourself will certainly affect you as you age, and eventually your wallet, as well.