It's not what you eat, it's who you are

The scientists summarized it in their paper: “The two major findings of this study were that there was a clear relation between the body-mass index of biologic parents and the weight class of adoptees, suggesting that genetic influences are important determinants of body fatness; and that there was no relation between the body-mass index of adoptive parents and the weight class of adoptees, suggesting that childhood family environment alone has little or no effect.”

In other words, being fat was an inherited condition.

Link: Genes Take Charge, and Diets Fall by the Wayside - New York Times