And the worst part is, you don’t even care.

Could your best friend make you fat?

Researchers who have studied “networks” of obesity think so: they found that if someone’s friend becomes obese, that person’s chances of becoming obese increase by more than half.

Siblings and spouses also have an influence, although a reduced one — people whose siblings became obese were themselves 40 percent more likely to grow obese, while people whose spouses became obese were 37 percent more likely to.

“This is the first (study) to show how obesity spreads through the social network from person to person to person,” James Fowler of the University of California, San Diego, who worked on the study, told a telephone briefing…

If someone became obese, their friends were 57 percent more likely to become obese over the 32 years, they found. If people named one another as contacts, they were 171 percent, or more than double, as likely to become obese if the other did.

The good news is it works the other way too. Exit question: Isn’t the obvious healthy solution to lead life as a shut-in with no contact with the outside world beyond one’s own cable modem? Ahem.