It's common knowledge that Americans live in an environment that promotes obesity. But, despite years of warnings, they're getting fatter than ever. The Centers for Disease Control and Duke University have reported that one third of children from two to 19 are overweight, and by 2030, 42 percent of adults will be obese. The question is what to do. Is the food industry just like Big Tobacco, marketing products that are harmful to health, rather than being nutritious? Is it time for new regulations? Is it all about brain chemistry? Are there cultural pressures that make some Americans fat because they want to be? Public agencies, universities and healthcare organizations conducted a conference this week called "The Weight of the Nation," and next week HBO will air a four-part series by the same name.