Does obesity breed obesity? A 2007 study out of Harvard University found that hanging out with fat people increase your chances of being fat. Now, based on the result of that study comes a new study from the Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology predicting obesity rates in the U.S. will slowly climb for another 40 years, at which point 42 percent of the population will be obese. Not just overweight, but obese. That finding contradicts previous predictions that the obesity rate has topped at its current rate of 32 percent of the U.S. population.

So is the solution as simple as not hanging out with big people, a solution that, presumably, would result in fewer and fewer big people to hang out with and, eventually, no big people to hang with?

No, according to University of Alabama at Birmingham obesity researcher David B. Allison. In another study, this one appearing in the Nov. 24 British journal “Proceedings of the Royal Society B,” Allison says it’s not even as simple as moving more or eating less. In fact, he claims, why we keep growing is a complex mystery.

Allison’s fascination with the obesity epidemic was piqued after checking out the marmoset population at the Wisconsin Non-Human Primate Center. He noticed that the entire population showed “pronounced weight gain” over time, yet after checking with staff at the center there was no obvious reason why. He began looking at other populations of mammals that lived with or around humans, from monkeys and chimps in research labs to feral cats in Baltimore. He wound up studying 24 sets of animals in all — and in all 24 sets the animals gained weight.

“The consistency of these findings among animals living in different environments, including some where diet is highly controlled and has been constant for decades, suggests the intriguing possibility that increasing body weight may involve some unidentified or poorly understood factors,” Allison told Science Daily.

Allison and Yann Klimentidis, Ph.D., a post-doctoral trainee in the School of Public Health and co-author of the study are investigating some of those “unidentified or poorly understood factors.” Among their initial suppositions, expressed to Science Daily:

Light. “Studies have shown that subtle changes in the amount of time spent in light or dark environments changes eating habits. Allison wonders if increased light pollution in our industrial society may play a role.”
Viruses. Infection with adenovirus-36 is associated with obesity, and the presence of antibodies to AD36 correlates to obesity in humans. Could AD36 or other infectious agents be contributing to obesity in populations?”
Epigenetics. “Genetic modifications brought about by any number of environmental cues such as stress, resource availability, release from predation or climate change.”

Again, Allison says the reasons behind our growing waistline are likely numerous and complex: don’t expect a silver bullet to emerge. Upshot for you: Keep eating well, keep moving.

Photo: What’s making this marmoset fat?