Here's a link to an interesting article that explores how the chemicals in the food we eat may have at least as much influence on our body weight as the calorie content.
http://www.theatlantic.com/health/print/2012/03/whats-really-making-us-fat/254087/
http://www.theatlantic.com/health/print/2012/03/whats-really-making-us-fat/254087/