Adam Drewnowski and his colleagues at the University of Washington have been doing a series of papers on the cost of food per calorie. The latest is a research brief answering the question, "Can low-income Americans afford a healthy diet?" Not really, they say. Federal food assistance assumes that low-income people spend 30 percent of their income on food, but that assumption was based on figures from an era when housing, transportation, and health care costs were much less.

As Drewnowski has shown repeatedly, healthier foods cost more, and sometimes a lot more, when you look at them on a per-calorie basis. Here's an excerpt from his report:

Studies on the social and economic determinants of health have shown that persons and groups of higher socioeconomic status (SES) have lower rates of obesity, type 2 diabetes, and cardiovascular disease (1). The literature suggests that some of the observed disparities in health may be related to disparities in diet quality (2-5). More affluent people are not only healthier and thinner but also consume higher-quality diets (6). It is not clear whether the more favorable health outcomes can be attributed to better diets, higher SES, or some combination of both (7).

The energy density of a diet (ie, available energy per unit weight) (8) is one indicator of diet quality. Lean meats, fish, low-fat dairy products, and fresh vegetables foods, sweets, candy, and desserts (9,10). Whereas energy-dense foods tend to be nutrient-poor, foods of low energy density provide more nutrients relative to kilocalories (11). An inverse relation between energy density and nutrient density has now been demonstrated both for individual foods (11) and for total diets (12).

[...] The important question is whether higher-quality but more costly diets are more likely to be consumed by more affluent persons. A key challenge in nutritional epidemiology is to make sure that persons or groups characterized by a given eating pattern do not differ in some fundamental yet unobserved way from persons with another type of eating pattern. Given that higher SES groups often have both higher quality diets and lower disease risk, epidemiologic studies tend to treat SES as a potential confounder. To reveal associations between dietary exposures and chronic disease risk, studies have adjusted for SES (38) whenever such variables were available. Our study had a different purpose, focusing on indicators of SES as exposure variables, and exploring the association between SES measures and dietary energy density and energy-adjusted diet cost.

Read the full report here.