Is obesity contagious?

I don’t know if you recall this article from the New Scientist discussing whether obesity is spreading through social norms.

However, there may be another pathway.

A 2007 Scientific American article mentions that bacteria can cause subjects to gain weight faster.

For one thing, bacteria produce chemicals that help us harness energy and nutrients from our food, Huffnagle explains. Germ-free rodents have to consume nearly a third more calories than normal rodents to maintain their body weight, and when the same animals were later given a dose of bacteria, their body fat levels spiked, even if they didn’t eat any more than they had before.

One day, we would not longer recognize ourselves as distinct organisms, but as composites.