Of or relating to a factor that causes or tends to cause obesity.
"We know that most 70-year-old women who are fat were not obese as children," Horlick said. "But today we have an unprecedented epidemic of childhood obesity, and kids are growing up in an 'obesogenic' environment, which did not used to be the case."
Sandra G. Boodman, "Fat Kids, Bad to the Bones," The Washington Post, July 3, 2001
Our environment is obesogenic. The level of physical activity it encourages is extremely low, so we don't burn as much energy. Parents are loathe to allow their children to play outside because it's dangerous, riding a bike is suicidal and trying to find the stairs in a building is an exercise only in ingenuity. On the other side of the equation our food supply has gone from low energy, high roughage to being dominated by fat.
Hilary Bower, "Selling the Big Issue," The Independent, November 17, 1996
English may have the biggest lexicon of any language in the world, but there are still many gaps that need to be filled in. For example, we still need a word for the mixture of surprise and disappointment you feel when you call a person expecting to get their voice mail but they answer live, instead.
Today's word is a gap-filler because it gives us a way to describe those things that lead to obesity. It gets there by scrunching together the word obesity and the suffix -genic, "producing; generating." Its leap from the labs to the mainstream appears to have happened around five years ago (see the earliest citation).