Obesity and the food environment: dietary energy density and diet costs.

The highest rates of obesity in the United States occur among population groups with the highest poverty rates and the least education. The impact of socioeconomic variables on obesity may be mediated, in part, by the low cost of energy-dense foods. The observed inverse relationship between energy density of foods, defined as available energy per unit weight (kilocalories per gram or megajoules per kilogram), and energy cost (dollars per kilocalorie or dollars per megajoule) means that diets based on refined grains, added sugars, and added fats are more affordable than the recommended diets based on lean meats, fish, fresh vegetables, and fruit. Taste and convenience of added sugars and added fats can also skew food choices in the direction of prepared and prepackaged foods. Paradoxically, attempting to reduce diet costs may lead to the selection of energy-dense foods, increased energy intakes, and overweight. The present energy-cost framework provides an economic explanation for the observed links between obesity and the food environment, with diet cost as the principal intervening variable. If higher food costs represent both a real and perceived barrier to dietary change, especially for lower-income families, then the ability to adopt healthier diets may have less to do with psychosocial factors, self-efficacy, or readiness to change than with household economic resources and the food environment. Continuing to recommend costly diets to low-income families as a public health measure can only generate frustration and culpability among the poor and less-well educated. Obesity in America is, to a large extent, an economic issue.