During the past three decades, levels of excess weight and obesity have risen significantly in the United States. The reasons are physical, economical and sociological. The second half of the twentieth century is characterized by changes in the diets and levels of activity in the American society. Recent studies that focus on simple explanations that are based on a few determinants or classes of determinants are inadequate in explaining the recent rise in obesity. Cross-sectional and time series data are analyzed with a variety of statistical techniques. This paper empirically examines the factors correlated with the drastic increase in excess weight in the United States. Demographic characteristics (e.g., race and gender) and income level are significantly related to obesity. Controlling for these factors, energy expenditure in physical exercise are also linked to obesity. This study suggests that policies that merely target on food consumption and physical exercise levels are likely to be inadequate. Successful policies will have to produce specific messages that are relevant for distinct cultural, racial, gender, and income groups. Examples of such group-specific messages are provided.