For most of the 20th century, North American food consumption was relatively stable, but the 1980s marked the beginning of a dramatic shift. We're eating, on average, 200 calories per day more than we did just thirty years ago. We're eating larger portions, and we're eating more often. What happened to bring about this sudden change? In this two-part series Jill Eisen explores the politics, economics and science of overeating. When it comes to food America is the land of plenty. Food is everywhere and the portions are humungous. It's no surprise that the US is ground zero for what's been called "the obesity epidemic." Canadians aren't far behind. It's no secret. We North American's have gotten fatter. But what's surprising is the just how fast it happened. For most of the 20th century, our average weight was fairly stable. Then suddenly, in 1980, something changed. By 2010, the average adult had gained a staggering 20 pounds, and obesity rates had skyrocketed. The usual suspects are eating too much and exercising too little. But why 1980? What happened to cause such a dramatic shift in the way we eat?