Declining Food Prices
The real price of unhealthy foods has been declining for decades. An analysis of Consumer Price Index (CPI) data found that the real price of vending-machine food had dropped during 1978–2007 by about 11 % and soda had dropped by about 38 %, but the real price of fruit and vegetables had increased by about 18 % . Kuchler and Stewart  found that this price increase for fruit and vegetables has been driven by new produce items that incorporate labor-saving innovations (i.e., “prepared” produce such as washed and bagged spinach, broccoli florets, and baby-cut carrots). Their study analyzed price trends for unprepared produce that remained unchanged between 1980 and 2006 and showed that price trends for unprepared produce were similar to those for the less-healthy categories of snacks and desserts. This implies that consumers who wish to economize financially by purchasing unprepared (rather than prepared) produce face an additional time burden, as they bear the time cost of labor such as washing, peeling, cutting, and chopping the produce.
In addition, Lakdawalla and Philipson found that the price of food fell relative to the price of non-food items from 1976 to 1994. This relative decrease in the price of food may have promoted overeating—one component of unhealthy eating—because the price of food rose less than inflation and was thus comparatively more affordable than other goods . However, this trend of declining relative prices for food compared to non-food recently reversed as food prices surged in 2007 and 2008 .
Total Cost of a Healthy Diet
The Center for Nutrition Policy and Promotion’s Thrifty Food Plan (TFP) is a national standard for a healthy diet at minimal cost and is used as the basis for maximum Supplemental Nutrition Assistance Program (SNAP; formerly the Food Stamp Program) allotments . The TFP assumes that all food is prepared at home and minimizes deviations from currrent dietary patterns. The TFP finds that it is possible to eat healthy for low cost: the TFP budget in 2008 for a family of four was $136 per week, of which $54 (40 %) was earmarked for fruit and vegetables. However, adherence to the TFP imposes significant time costs (e.g., the need for bargain-hunting, traveling to and from the store, shopping, food preparation, cleanup). Because of these and other limitations, the TFP has been criticized as unrealistic [8, 9•].
Mediterranean dietary patterns are considered healthy, partly because they are associated with lower incidence of cardiovascular disease and lower rates of total mortality [2••]. The diet can be expensive , but Goulet et al.  found that middle- and upper-class consumers can achieve it (at no extra cost) by focusing on the lower-cost foods from the diet (e.g., pulses, legumes, nuts, dried fruit, canned fish) and buying less red meat, sweets, and fast foods in favor of healthy foods. However, Goulet et al. note that their study of the affordability of Mediterranean dietary patterns underrepresented people of low socioeconomic status, so no conclusions could be drawn about this population who may very well find such diets unaffordable.
Energy-dense foods have a high ratio of calories per gram. Some researchers [12–15] argue that low-income consumers eat energy-dense foods (e.g., sweets, fast food, many snacks) because these foods are a cheaper source of calories than low-energy-density foods (e.g., fish, vegetables, fruit).
This claim has been contentious for a few reasons. First, the negative association between energy density (calories/gram) and cost per calorie ($/calorie) may be spurious because of mathematical coupling, in which two variables that share a common component are compared . Second, consumers with energy-dense diets in many cases spend the same amount of money on food as those with less-energy-dense diets —so healthy eating is financially within reach for many consumers with energy-dense diets [17, 19••]. Third, if consumers chose foods based on cost per calorie, then the current trend of marketing foods with phrases such as “low-calorie” would not exist because such marketing claims would imply a poor bargain in terms of cost per calorie .
Weighing in on this debate is a recent study by Carlson and Frazão [19••] comparing various measures of food cost. The authors systematically compared the cost of healthy and unhealthy foods using three different cost metrics: price per 100 calories, price per 100 edible grams, and price per average portion. They found that healthy foods are actually less expensive than unhealthy foods when cost is measured as price per 100 edible grams or price per average portion. (Healthy foods were defined as those containing at least half a portion size of a Dietary Guidelines major food group and containing low to moderate amounts of saturated fats, added sugars, and sodium.) These findings underscore how important the choice of cost metric is when discussing the cost of healthy versus unhealthy foods.
Diet Quality, Income, and Spending
If healthy diets cost more, then consumers who spend more may eat healthier. The weight of the literature suggests that consumers who spend more on food tend to have healthier diets as meaured by the Healthy Eating Index [22, 23]. On the other hand, individuals who switch to a healthier diet—such as pregnant women following a low-glycemic diet  or obese children undergoing dietary treatment —can do so without increasing their daily dietary costs.
If healthy diets are more expensive, then poorer people should have worse diets. Two systematic reviews [26, 27••] support this conclusion, finding that consumption of fruit and vegetables was positively associated with income. In England, the poor had worse diets and ate less fruit . Poor consumers in the Phoenix, Arizona, area had worse diets, with the exception of lower quantities of saturated fat . On the other hand, a study using 2001–2002 National Health and Nutrition Examination Survey data showed that income had little influence on diet quality .
We conclude that there is a weak positive relationship between food spending and healthy diet. Although the TFP shows that it is possible to eat healthy at low (monetary) cost, adhering to the TFP guidelines imposes a high utility cost on individuals (such as time), so few people actually follow it. Economic theory suggests that people maximize utility subject to their budget constraint; as their budget constraint relaxes, people can purchase food that provides more utility in terms of health, leisure time, and palatability.
Time costs are driven by the opportunity cost of time. People may therefore eat healthier during brief recessions because joblessness increases leisure time, making it cheaper to undertake health-producing activities such as preparing healthy meals . (However, during a long-lasting economic downturn, reductions in employment and income likely do not lead to healthier diets.)
Food prepared at home (FAH) is generally healthier than food away from home [32, 33] but it requires the time cost of activities such as grocery shopping, food preparation, and cleanup. These costs can be substantial. Economists have estimated the time costs of FAH by multiplying the opportunity cost of people’s time (e.g., wage rate) by the number of hours spent in FAH activities. The daily household time cost of food preparation and cleanup was $20.43 (50 min) per SNAP household and $21.62 (45 min) per non-SNAP household for people who performed housework and market work in 2003–2006 [34••]. Women have a higher time cost than men [35••].
Compared to the general population, SNAP participants have higher time costs and lower food input costs for FAH. But if SNAP participants were to follow the TFP, their daily time costs would have to increase further, from the current $8.66 (38 min) to $15.84 (72 min), while their monetary costs would marginally increase from $8.40 to $8.56 [35••]. That is, when total TFP time costs are monetized, they are 85 % higher than the cost of the food itself. In other words, the TFP is expensive once its associated time requirements are factored in [8, 35••]. Households' actual SNAP participation status was not known in this study [35••], so the authors inferred SNAP participation from household demographics.)
Time is also required to develop cooking skills in the first place. Cooking skills may have deteriorated over the last several decades, leaving many people without the skill to time-efficiently prepare healthy meals . (Declining confidence in one’s skills may also be an issuel .) A study of young adults 18–23 years old found that 18 % of women and 23 % of men cited their inadequate cooking skills as a barrier to food preparation; the study also found an association between cooking and healthy diet . Cooking skill is positively associated with consumption of fruit and vegetables and negatively associated with consumption of convenience foods .
Consumers also incur transportation costs (e.g., gasoline) while traveling to grocery stores. People who live in food deserts—areas with limited access to affordable, healthy food—often incur higher transportation (and time) costs because supermarkets are far from their homes [40, 41]. Low-income Americans are especially likely to live in food deserts, but evidence regarding socioeconomic disparities for other countries is scant .
Apart from grocery stores, access to healthy restaurants is also an issue. Restaurants in poorer Los Angeles County neighborhoods with a higher proportion of black residents have fewer healthy food options . Higher concentrations of fast-food restaurants exist in poor and minority communities, although further work is needed to understand if and how access to fast food impacts dietary intakes and health outcomes .
This section reviews the psychological costs of healthy eating—that is, the psychological stress caused by healthy eating or the pursuit of healthy eating.
Habit, convenience, preferences, and taste are important determinants of a diet. Taste is enhanced by fat, sugar, and sodium, which are prevalent in many unhealthy products [45, 46]. Food marketing caters to consumers’ preferences for these substances—and stimulates their demand for these products—by developing foods designed to hook consumers and by advertising especially to children [47, 48].
Perception also affects dietary behavior. When consumers see information touting the healthiness of a food, they often assume that the food has an inferior taste, and this assumption decreases their enjoyment of the product [49, 50]. When consumers are told that a food is healthy, they perceive it to be low in calories, which leads to overeating . Large portions increase the psychological costs of healthy diet as consumers are tempted to finish their portions, leading them to overeat . Furthermore, food vendors tend to supersize portions as the marginal cost of adding food to the portion is low . Competition between food manufacturers can reduce incentives to introduce smaller portions and packages, especially many consumers have self-control problems with limiting their consumption .
Healthy behavior in one dietary area can be compensated for by unhealthy indulgence in another . For example, consumers who take vitamins tend to eat less healthy, as they feel protected from negative health consequences . Thus, healthy dietary behaviors may increase psychological costs by requiring greater self-discipline in other dietary areas.
One important feature of a healthy diet is that its benefits often occur in the distant future, while its costs (e.g., perceived inferior taste) occur immediately. Uncertainty about the future , impatience, and future discounting  all increase the psychological costs of healthy eating. One way to alleviate such problems is to introduce a lag between the day one selects and pays for groceries and the day one actually receives the food, as this delay leads to healthier purchases [57•].
Physiology and sociocultural norms also affect the cost of healthy eating. For individuals with strong self-control, consumption of unhealthy food leads to earlier satiation of the desire for such foods, reducing the psychological costs of eating healthy . Genetic variations, as in the TAS2R38 gene, affect preferences for sugar, fat, fruit, and vegetables [59, 60]. Choosing unhealthy food is easier when one is alone and anticipates dealing only with one’s own guilt rather than with the shame of being witnessed . Exposing children to healthy eating early in life creates good dietary habits, which reduces the psychological costs of healthy diet in the future .
Impulse shopping is associated with the purchase of unhealthy foods, so curbing impulsive purchases of unhealthy foods is a psychological cost of healthy eating. Consumers are more likely to purchase unhealthy foods when they pay by credit card rather than cash because paying in cash feels more painful and this pain can curb impulsive purchase decisions .
The information costs of healthy eating are the time and effort required to obtain nutrition information and update one’s nutrition knowledge. Getting people to eat healthy may also require funding for education and informational campaigns designed to reorient people to a culture centered around healthy diets.
Researchers have identified three types of nutrition knowledge that promote healthy eating: 1) awareness that there is a link between diet and health (e.g., a link between saturated fat and heart disease), 2) knowledge of nutrition principles (e.g., recommendations on the percentage of calories that should come from fat), and 3) and knowledge of foods’ specific nutrient content (e.g., which foods have more fiber, fat, or cholesterol) [64, 65].
Providing consumers with nutrition information at the point of purchase reduces their information costs. By requiring that nutrition labels have a standardized format and be easy to read, the 1990 Nutrition Labeling and Education Act (NLEA) helped consumers use nutrition information if they were already motivated to search for and process such information  and improved the diets of consumers who used nutrition labels [67, 68]. Providing nutrition information to consumers can cost firms as well, as in the case of firms being required to comply with the 2010 Patient Protection and Affordable Care Act, which mandates nutrition labeling of menu items.
After finding nutrition information, consumers must then analyze it. Consumers spend an average of 12.3 s acquiring nutrition information for each grocery item they select . To calculate total time spent per shopper, this number would have to be multiplied by the number of grocery items that a shopper selects, and then added to the time cost for all other items that a consumer examines but does not ultimately select. This information cost may diminish somewhat over time as consumers learn the nutritional content of their favorite items but consumers may also have to continually spend time examining new products entering the market.
As nutrition science advances, consumers also face the cost of periodically updating their basic nutrition knowledge. Trans fat is a recent example. Consumers who were uninformed about the link between trans fat and poor health were unable to take advantage of the trans fat information that was added to the Nutrition Facts panel in 2006 [71, 72].
Costs of Longer Life Expectancy
Healthy diets extend life expectancy, which can result in extra costs due to age-related health conditions. The prevalence of chronic conditions (e.g., cardiovascular disease, diabetes, cancer, dementia, physical disability) increases with age .