Obesity and Socioeconomic Status

Obesity follows a socioeconomic gradient in which disease burden is greatest among those with limited economic resources. Regardless of race or ethnicity, obesity disproportionately affects individuals of lower socioeconomic status (SES). Findings from the National Health Interview Survey, reported that 26 percent of the population below the poverty level is obese, compared with populations in the highest income bracket, which had a 15 percent prevalence of obesity.

The inverse relationship between SES and obesity begins in adolescence and continues through the life span. In limited-resource women, the weight gradient actually increases with age. Limited-resource women tend to gain more weight each year than comparable populations of women with higher SES. A number of potential mechanisms have been suggested to explain the relationship between limited-resource individuals and obesity, including overconsumption of inexpensive, high-energy foods; periods of overeating followed by periods of deprivation, also known as the “food stamp cycle”; and limited access to recreational resources.

Overconsumption of Inexpensive Foods

In terms of total food purchases, limited-resource families spend nearly 34 percent of their disposable income on food, compared with 8.7 percent spent by [Page 537]higher-income families. The disparity between the percentage of money spent by limited-resource populations compared with higher-income populations is great enough such that food spending effectively functions as an indicator of affluence. Although limited-resource families spend a higher percentage of their incomes on food, these families actually spend less total money on food. If limited-resource families spent as much per person on food as their higher-income counterparts, they would outlay more than 54 percent of their total disposable income on food alone. Instead, limited-resource families appear to maximize their money by purchasing less costly foods.

It is well established that higher diet quality is associated with higher incomes and with lower rates of obesity. When financial resources are lacking, nutrition and health tend to function in a secondary role to economic considerations. Households reduce food spending by changing the quality or variety of foods consumed before they reduce the quantity of food eaten. As a result, while families may get enough food to avoid feeling hungry, they may be poorly nourished because they cannot afford a consistently adequate diet that promotes health and averts obesity. The need to satisfy hunger overrides considerations for health.

Inexpensive Foods: Energy Dense and Less Nutritious

Energy density is defined as the quantity of energy per unit of edible weight and is often expressed in kilocalorie per kilogram (kcal/kg) of food. The energy density of foods is a function of their water content. Low energy-dense foods are heavily hydrated and tend to be rich in nutrients. These include lean meats and fruits and vegetables. High energy-dense foods are dry, contain large quantities of fat and sugar and tend to be nutrient poor. Examples include refined grains, most fast foods, soft drinks, and snack foods, such as potato chips and cookies.

High energy-dense foods usually cost less than low energy-dense foods. A unit of energy from high-fat, high-sugar foods, such as potato chips and cookies, tends to be less expensive than a unit of energy from fruit and vegetables. For example, consider the relationship between energy density (kcal/kg) of the following foods and their “energy cost” as expressed in kcal/$. The energy cost of potato chips is 1,200 kcal/$ and the energy cost of soft drinks is 875 kcal/$. In contrast, the energy cost is approximately 250 kcal/$ for fresh carrots and approximately 170 kcal/$ for frozen orange juice. The difference in cost per calorie between the high energy-dense foods and those of lower density is more than sixfold.

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