This study examined diet cost and diet quality in a sample of northeast central Chinese adults. Overall, nutrient density, the mean adequacy ratio (MAR), and dietary energy density were independent predictors of the daily energy-adjusted diet cost. Whereas the more energy-dense diets cost less, the more nutrient-dense and nutritional quality diets were found to cost more. These associations were independent of each other and were not influenced by age, sex, energy intake, or family income.
Participants reported spending ¥14.05 on food and non-tap water beverages during every 24-hour observation period, while spending ¥19.14 per 2000 kcal, which were similar to the estimated mean expenditures on food at home (¥19.99/2000kcal) based on retail prices on the Nantong city of China[25], and were similar to the cost of school-aged children in Southwest China (¥11.0/1000kal)[14]. The differences between several socio-demographic characteristics and daily diet cost or daily energy-adjusted diet cost were explored. As we know a major determinant of economic well-being is the level of income that a household receives. The present results confirm past observations that family income appears to be an important correlate with food expenditure patterns[26].
This study showed that participants in the higher quartiles of daily energy-adjusted diet cost spent more on fruit, high protein foods, and other food groups, and less on the grain foods. At the nutrients level, the lower cost diets contained more energy, total fat, and carbohydrate, and contained fewer micro-nutrients such as vitamins A, and C. No matter from the point of view of food or nutrients, it is consistent with the recommendations of the Chinese Guidelines for Chinese Residents[27], which also was similar to that of a study in the America[28].
Subjects who closely adhered to the high-quality diets paid more for food consumption than those who weakly adhered to these dietary patterns. Meanwhile, increasing the daily energy-adjusted diet costs was associated with a positive change in diet quality. The present data confirm previous observations, based on a representative sample of the French population[29] and the Americans[28], that lower-cost diets are energy-dense and nutrient-poor. By contrast, higher quality diets cost more. Several studies have emphasized that the food budgets of the poor are insufficient to obtain a balanced diet[30]. Even when low-income groups develop efficient purchasing strategies[31], the food budget may not be adequate to procure the recommended diet.
Dietary energy density is one index of the overall quality of the diet[32]. Diets high in whole grains, lean meats, fish, and fresh vegetables, and fruit have a low energy density and a high content of vitamins and minerals[32], which are more costly per kilocalorie than are energy-dense diets rich in fats and sweets[33]. The present data, based on a sample of Chinese adults, are consistent with published findings on diets of energy density and diet quality of a large representative sample of adults in the United States[11, 28] and France[10, 34]. A study from China shows that vegetables and fruits had the lowest energy density, but their food prices were the highest per unit of energy[25]. The ability to adopt more healthful and, therefore, more costly diets can be viewed as behavior as an economic issue, which may have implications for some of the current strategies for health promotion.
The concept of nutrient density is critical to a better understanding of the relation between diet quality and its cost. Our finding that daily energy-adjusted diet cost was inversely associated with NRF9.2, MAR reflects the results of several other studies. Drewnowski et al. found that nutrient density score were positively associated with diet cost per 100g[35]. Meanwhile, from a nutritional quality point of view, Drewnowski et al. also found that nutrient adequacy scores was positively associated with diet cost per 1000 kcal[35] and Matthieu et al. showed that for a given energy intake and energy density, each 10% increase in MAR led to a 13% increase in estimated diet costs per 10 MJ[36]. In general, economic forces may hold the key to dietary change, given that the more nutrient-dense foods and higher-quality diets tended to be more expensive on a per calorie basis[37]. Meanwhile, there are also some examples where changing food prices can improve dietary quality or improve clinical outcomes. Beydoun et al found that an annual rate of change in the monetary value of the diet may have a stronger impact on dietary quality among American urban adult women and above-poverty individuals[38]. Anne Magnus et al. found that the cost-effectiveness of a 20% price discount on healthy food and beverages with and without consumer nutrition education led to a net loss of population health − 36 95%CI (-47,-25) or -21(-28, -15) disability-adjusted life years (DALYs) respectively in remote Australian[39]. Thus, for health promotion campaigns to be effective, it is essential that food prices are indeed a policy concern to ensure a nutritious food supply now and for future generations.
Arguably, not all healthier diets are necessarily associated with higher costs. It has been reported that healthy diets can be obtained at different cost levels. Mexican–Americans were found to consume higher-quality diets with lower costs than other populations[40]. And Zhou et al. found that it was not considered that the more expensive the food was, the higher the nutritive value it had in each group of foods[25]. Because the more food is processed, the more nutrients are lost, and the higher the unit price is. These studies highlight the need to identify dietary patterns that are both healthful and affordable for Chinese adults.
The present study is the first to provide evidence for an inverse relationship between dietary quality (from the dimensions of nutrient density, energy density and, nutrient adequacy) and daily energy-adjusted diet costs among Chinese adults. However, there are important limitations. First, in the absence of food expenditure data, the model was based on the national website and retail food prices. In effect, the model estimated what each diet cost, as opposed to what the consumer paid for it. However, a similar method was used in previous observational studies[41]. Secondly, the modeling of diet cost was based on the strong assumption that most foods consumed, other than fast foods, were purchased at retail and prepared at home. The validity of the diet cost estimates for individuals who frequently consumed away-from-home foods and beverages would likely be below. It is worth noting that this limitation is common to epidemiologic studies on dietary exposures. Furthermore, the participants' food records were only collected 2 days by 24-h dietary recalls method. Thus, the data may not provide an accurate reflection of daily dietary behaviour and food group. Thus, findings may be limited in their generalizability. Finally, our data were cross-sectional, and therefore, possible causal pathways indicated by the mediation analyses cannot be confirmed. Despite these limitations, our estimates of daily energy-adjusted diet costs and diet quality were comparable to those obtained from other sources. More research on larger and more diverse populations will be needed to establish whether the trade-offs between cost and quality of the diet revealed our sample also exists in other groups.