Using the thrifty food plan to assess the cost of a nutritious diet.

The federal government's Thrifty Food Plan (TFP) minimizes the difference between a proposed food plan and a current consumption bundle, subject to cost and nutrition constraints. This article adapted the TFP framework to estimate the cost of a nutritious diet, distinguishing between nutrition constraints based on food categories (meat, vegetables) or nutrients (saturated fat, calcium). The official cost target for the TFP was sufficient if one tolerated a very high difference from current consumption patterns, or if one used nutrition standards instead of MyPyramid food category standards. In other scenarios, with different constraints, the official cost target was insufficient.

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How much does a nutritious diet cost?

This question is central to debates over U.S. anti-hunger and nutrition policy. The benefit level for more than 28 million low-income participants in the Supplemental Nutrition Assistance Program (SNAP), formerly called the Food Stamp Program (FSP), is related to the federal government's official estimate of the cost of a "thrifty" but nutritious diet (Carlson et al. 2007). This question also matters for nutrition policy more broadly, because one leading explanation for the current epidemic of obesity-related chronic disease emphasizes the comparatively low cost of energy-dense foods and the high cost of healthier foods (Drewnowski and Specter 2004).

The estimated cost of a nutritious diet depends systematically on the definition of "nutritious." In Stigler's famous 1945 application of linear programming, the minimum cost required to meet narrowly defined nutrition targets was only pennies per day (Stigler 1945). He acknowledged that his cost estimate would make dietitians unhappy, and implied that they were too generous in their "cultural requirements" for palatability, variety, and prestige, which "should not be presented in the guise of being part of a scientifically-determined budget." By contrast, researchers at the Brigham and Women's Hospital in Boston estimated the monthly cost in 2003 of a "heart-healthy" and "culturally appropriate" diet for a family of four in the low-income neighborhood of Roxbury to be $692, which was $242 higher than maximum food stamp benefit at the time (Johnson et al. 2004).

The U.S. Department of Agriculture (USDA's) Thrifty Food Plan (TFP), revised most recently in 2006, offers a useful framework for studying the cost of a nutritious diet. USDA generates the TFP by solving a constrained optimization problem, choosing a diet that is as similar as possible to the current consumption pattern for low-income Americans, while simultaneously meeting a cost constraint, food group constraints drawn from the MyPyramid nutrition education materials, nutrient constraints from the Dietary Guidelines for Americans, and other miscellaneous constraints.

The maximum benefit for the FSP is related to the value of the TFP, but this policy role is commonly misunderstood. Although the TFP is described as "the basis for maximum food stamp allotments," each revision of the TFP takes an inflation-adjusted cost of the preceding plan as the cost constraint for the new food plan. The official TFP does provide the food group quantity weights that are used in USDA's annual inflation adjustments for FSP benefits, but it would make only a modest difference in the time trends if the quantity weights in the Consumer Price Index (CPI) for food at home had been used instead. The main policy role of the TFP revision is to confirm that the previous budget allotment still suffices to purchase a nutritious diet. TFP revisions after the 1970s have not sought to reopen the more fundamental question of how much a nutritious diet should cost in the first place.