Observational studies have established consistent associations between degrees of nutrient intakes and health outcomes. The present study, for the first time, examined degrees of nutrient intakes, for every key nutrient in the diet, in relation to estimated diet cost and participant SES. The study took care to follow standard epidemiological adjustment and stratification techniques.
There were significant findings. First, lower intakes of beneficial nutrients were associated with lower diet costs. Study respondents with lowest intakes of dietary fiber, vitamins A, C, D, E, and B12, beta carotene, folate, iron, calcium, potassium, and magnesium were also those who had lowest estimated diet costs. Coincidentally, some of these nutrients have been identified as nutrients of concern by the 2010 Dietary Guidelines 
. By contrast, higher intakes of fats and added sugars, typically associated with adverse health outcomes, were associated with lower diet costs. These are the nutrients to limit, as identified by the 2010 dietary guidelines 
. Based on current eating habits, compliance with dietary guidelines is likely to entail higher diet costs for the consumer.
Second, persons with lower cost lower quality diets were more likely to be from lower SES groups. These findings are consistent with the existing literature on SES and diet quality 
and diet cost 
However, not all beneficial nutrients were equally expensive. The most pronounced positive gradient with diet cost was seen for vitamin C, beta carotene, potassium and magnesium – nutrients primarily obtained from fruits and vegetables. By contrast, calcium and vitamin D showed a weaker associations with diet cost, likely because milk and milk products are relatively inexpensive 
. Iron and folate also showed a weak association with diet cost, which may reflect the ubiquity and relatively low cost of grain products fortified with iron and folate. Further, gender differences were observed in some of these associations. Women with higher intakes of certain beneficial nutrients such as potassium and magnesium tend to have significantly higher diet costs as compared to men. This could be attributed to overall higher intakes of such nutrients per kcal among women than men, and that women also tend to choose more expensive sources of such nutrients. A recent study based on national level health survey found that women tend to have higher consumption of fruits and vegetables while men consume more meats 
. Consistent findings were obtained in the present sample (results not shown).
There is clearly a need to identify and promote inexpensive food sources of key nutrients in order to improve the dietary quality of lower SES groups. A recent analysis of the 4 shortfall nutrients in the US diets showed that, in the context of current eating habits, complying with potassium guidelines was a particular challenge 
The present study had certain limitations. First, estimates of nutrient intakes and diet cost were each based on FFQs, which has certain known biases 
. However, it is a useful tool to make comparisons across subjects and has been widely used in nutritional epidemiological studies. Second, diet cost estimates do not represent actual expenditures made by the study sample. Instead, these represent the lowest monetary value of the diet at which foods were available in the key retail supermarkets in the Puget Sound area. This method of estimating diet cost, in fact, offered certain advantages: a) it did not allow variation in diet cost, among individuals, simply due to differences in price of the same food item across stores, or due to differences in the amount spent while eating out, b) the use of retail food prices to calculate individual diet cost is the only method of estimating diet cost in the existing literature 
and opens the door to individual level studies on diet cost, diet quality and health. Third, the average calorie intakes observed in the present sample were lower. However, this could be attributed to higher proportion of older adults (mean age of the present sample was 56 years) as these values were comparable to calorie intake estimates observed in National Health and Nutrition Examination Surveys (NHANES, 2001–08) and other health studies for that age, particularly for women. Fourth, the present study was based on cross sectional data, hence, associations observed between SES, diet cost and nutrient intakes cannot be causally interpreted.
Nonetheless, the present findings have implications for future research. First, diet cost variable ought to be taken into account in future studies on diets and disease risk. Second, further research is needed to identify cheaper ways of promoting beneficial nutrients to the consumer, particularly among lower income and lower education group.