The recent upward trend in the adult obesity rate is attributable to an energy imbalance, where people consume more calories than they expend. Between 1970 and 2004, Americans increased their daily consumption by an average of 300–500 calories, and the quality of diets changed. The typical American diet today consists of foods and beverages with a greater degree of processing, including more calories consumed from restaurants, sugar-sweetened beverages (SSBs), and ready-to-eat and ready-to-heat foods. Meanwhile, although physical activity in leisure has increased slightly, physical activity in work, housework, and travel has declined steadily. The complex interaction between diet composition, eating and physical activity behaviors, and human physiology makes it difficult to pinpoint the exact mechanism through which prevalence of obesity has increased.