The search query combined the terms related to foods/diet patterns, price, setting and time (supporting appendix 1). Because our focus was on contemporary price differences related to healthfulness, and because such price differences could vary in earlier decades, we focused our search on studies having collected price data in the year 2000 or later. Additional articles were identified by expert consultations, and hand-reviews of reference lists and the first 20 “Related citations” in PubMed for all studies included after full-text review. Systematic searches were conducted using MEDLINE (via PubMed) for all eligible English language articles published through December 2011.
Search strategy and selection of articles To address each of these key gaps in knowledge, we performed a systematic review and meta-analysis of the evidence for relationships between the healthfulness of foods/diet patterns and their price, including consideration of different food groups and diet patterns, definitions of healthfulness, intensities of the contrast and units of comparison (calorie, serving and daily diet). In particular, price differences per calorie may be limited by reverse causation, as healthier foods (eg, fruits and vegetables) often have fewer calories and evaluation of price differences per serving may alter the conclusions. Finally, price differences may vary by the unit of comparison, for example, per serving, per calorie, or per day. The intensity of the health contrast could also affect the price difference for example, a fast food meal versus a healthier home-cooked meal is a more extreme comparison than a low-fat versus high-fat cookie. Price differences may also depend on how healthfulness is defined, ranging from definitions based on single nutrients (eg, fat or sugar content) to those based on food types or more complex diet patterns.
Many studies compare healthier and less healthy versions of the same food (ie, more vs less healthy grains), while other studies examine the price differences of healthier vs less healthy overall diet patterns, containing very different foods. For example, price differences may vary by the foods or diets being compared. In addition, little is known about the potential heterogeneity of this relationship. Yet, while several studies have evaluated whether healthier foods or diets cost more, 6–10 the evidence has never, to our knowledge, been systematically reviewed nor quantified to critically evaluate all the evidence for the relationship between healthfulness of foods or diet patterns and price. One of the most commonly described barriers is cost: conventional wisdom holds that healthier foods and diets are more expensive than less healthy options, an assumption which has become “a reflexive part of how we explain why so many Americans are overweight.” 5 1–4 Many factors, including the availability and cultural acceptability of healthy foods, pose obstacles to the promotion of healthy diets. This is especially crucial for socioeconomically disadvantaged populations, who have less healthy diets and higher disease risk than higher socioeconomic groups. Consumption of a healthy diet is a priority for reducing chronic diseases including obesity, diabetes, cardiovascular diseases and several cancers.
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