In your experience, is weight gain/loss a simple ratio of calories in to calories out?

I had an interesting conversation with a scientist recently who told me about research showing that obesity increases when certain kinds of bacteria in the gut are eliminated. (She didn’t give me a citation, but here is an article for those interested.)

I think this is interesting because it really challenges the idea that weight change is simply a matter of how many calories you eat and burn. And could perhaps account for at least part of the rapid rate of increasing obesity.

What do you think? In your experience with weight gain/loss, has it been simply a matter of how much eat or don’t eat, and work out or don’t work out? Do you think research like this distracts from the real issue (eat less, exercise more) or could it be an important consideration in solving the obesity crisis?