Does social class predict diet quality?

There is an inverse relation between socioeconomic status and mortality. Over the past several decades death rates in the United States have declined, but it is unclear whether all socioeconomic groups have benefited equally. Using records from the 1986 National Mortality Followback Survey (n = 13,491) and the 1986 National Health Interview Survey (n = 30,725), we replicated the analysis by Kitagawa and Hauser of differential mortality in 1960. We calculated direct standardized mortality rates and indirect standardized mortality ratios for persons 25 to 64 years of age according to race, sex, income, and family status. The inverse relation between mortality and socioeconomic status persisted in 1986 and was stronger than in 1960. The disparity in mortality rates according to income and education increased for men and women, whites and blacks, and family members and unrelated persons. Over the 26-year period, the inequalities according to educational level increased for whites and blacks by over 20 percent in women and by over 100 percent in men. In whites, absolute death rates declined in persons of all educational levels, but the reduction was greater for men and women with more education than for those with less. Despite an overall decline in death rates in the United States since 1960, poor and poorly educated people still die at higher rates than those with higher incomes or better educations, and this disparity increased between 1960 and 1986.

Highest rates of obesity and diabetes in the United States are found among the lower-income groups. The observed links between obesity and socioeconomic position may be related to dietary energy density and energy cost. Refined grains, added sugars, and added fats are among the lowest-cost sources of dietary energy. They are inexpensive, good tasting, and convenient. In contrast, the more nutrient-dense lean meats, fish, fresh vegetables, and fruit generally cost more. An inverse relationship between energy density of foods (kilojoules per gram) and their energy cost (dollars per megajoule) means that the more energy-dense diets are associated with lower daily food consumption costs and may be an effective way to save money. However, economic decisions affecting food choice may have physiologic consequences. Laboratory studies suggest that energy-dense foods and energy-dense diets have a lower satiating power and may result in passive overeating and therefore weight gain. Epidemiologic analyses suggest that the low-cost energy-dense diets also tend to be nutrient poor. If the rise in obesity rates is related to the growing price disparity between healthy and unhealthy foods, then the current strategies for obesity prevention may need to be revised. Encouraging low-income families to consume healthier but more costly foods to prevent future disease can be construed as an elitist approach to public health. Limiting access to inexpensive foods through taxes on frowned upon fats and sweets is a regressive measure. The broader problem may lie with growing disparities in incomes and wealth, declining value of the minimum wage, food imports, tariffs, and trade. Evidence is emerging that obesity in America is a largely economic issue.