You are right, western food has had an adverse effect on Thai kids. Traditionally, Thais eat very healthy food in smaller amounts, but frequently, which keeps the metabolism running high. The spiciness also speeds up metabolism. If you ever notice how Thais eat, you will see them taking a bite or two to their plate at a time. When they have had enough to eat, the stop eating. Being the product of Depression Era parents, I was always told to "clean your plate".