Background
Low income is associated with a poor quality dietary intake [
1,
2]. Compared to those with higher income, lower income individuals consume fewer fruits and vegetables, more sugar-sweetened beverages and have lower overall diet quality [
1,
2].
Household food purchases are important to examine because they provide information about potential mediators of individual dietary intake, and have implications for intervention strategies to improve dietary intake and quality. Individual dietary intake is shaped in part by the household food purchases that create the home food environment [
3,
4]. Household food purchase receipt collection provides detailed, timely data on the type and cost of foods and beverages flowing into the home environment [
5]. Food purchase receipt data have been used to examine specific food categories of interest, nutrients and overall healthfulness of the home food environment. Low-income households purchase fewer fruits and vegetables, more sugar-sweetened beverages and fewer healthful foods compared with higher income households [
4‐
14].
The purpose of the present research was to examine differences in the quality of food purchased by household income level. Data are from an observational study of food shopping practices that included 202 urban households in a large city in the United States [
15]. It was hypothesized that lower income households’ food purchases would be lower in overall nutritional quality, and include fewer fruits and vegetables and more sugar-sweetened beverages compared with higher income households. A unique aspect of the present study was its examination of specific types of foods purchased and overall nutritional quality using the Healthy Eating Index 2010 [
16], and its inclusion of purchases from a variety of food stores, not just traditional grocery stores [
5,
6,
17].
Discussion
Household food purchases are important to examine because they may influence dietary intake quality, and are important potential intervention targets. In the present study, the overall nutritional quality of foods and beverages purchased was significantly lower among lower income households compared with higher income households. This remained significant with adjustment for education level, a strong correlate of both household income and diet quality. The specific food purchase categories that were associated with income were vegetables and dairy (HEI subscores) and frozen desserts (NDS-R food category). Vegetable purchases coded into the HEI subcategories were significantly positively associated with higher income-to-poverty ratio, and were marginally associated with purchases measured by NDS-R food categories coding. Dairy purchases, captured by the HEI subcategories, and frozen desserts, captured by the NDS-R food categories, significantly differed by income-to-poverty ratio.
The results of the present study are consistent with existing data regarding the association between income level and the nutritional quality of foods and beverages purchased [
6‐
14]. Food purchase data show that lower-income households purchase less healthful foods overall, fewer fruits and vegetables and more sugary beverages compared to households with higher income [
6‐
14]. The most recent comprehensive analysis of food purchase patterns from a nationally representative sample of 4826 US households showed that food purchase patterns among households of all income levels are lower in dietary quality than recommended [
4]. However, households that were participating in the federal food assistance program (called Supplemental Nutrition Assistance Program) purchased lower quality foods compared to households of comparable income that were not participating, and households with higher income. Overall Healthy Eating Index scores, fruits, vegetables and whole grains were significantly lower and empty calories significantly higher, among low-income households enrolled in SNAP compared with low-income households not enrolled in SNAP and higher income households [
4]. In another study, an analysis of 24,879 household food purchase receipts showed that food purchases by lower-income households were less healthful and included fewer fruits and vegetables than recommended, according to a standardized nutrient profile [
11]. In another study of 90 households with children, compared with higher income households, lower income households spent fewer dollars on fruits and vegetables and sweets and snacks, but spent a larger proportion of beverage dollars on sugary beverages [
7]. A study of 1003 households that used face to face interviews found that lower income households reported purchasing fewer fruits, vegetables and fiber, and more sugary foods, compared with higher income households [
9,
10]. In a study that used in-store shoppers’ purchase data, results showed that lower-income household purchases were lower in dietary quality per 1000 kcals purchased compared with higher income households’ food purchases [
8].
These findings further establish the link between income and the quality of the foods and beverages purchased by households. If diet quality is lower among lower-income groups, then food purchases may be a key intervention target. The present study indicates that lower income households are less likely to purchase recommended healthful foods such as vegetables, and spend a larger proportion of their grocery money on less healthful foods such as frozen desserts. Food assistance programs could help promote healthier food purchases through specific program guidelines, such as incentivizing the purchase of fruits and vegetables, or restricting the purchase of sugar-sweetened beverages or sweet baked goods [
19,
22]. These strategies have been shown to be effective in changing low-income households’ food purchases in community-based randomized trials [
18,
19,
22].
The present study was limited in its ability to separately examine income and education in relationship to food purchasing behavior. Income and education are closely intertwined, and may have independent or synergistic effects on food purchasing behaviors. It is noteworthy that many of the observed associations between income and food purchasing variables were substantially attenuated when adjusting for other socioeconomic variables such as education and race. The independent effects of education and income on food purchases warrants closer study, since intervention strategies may be differentially effective, depending on the answers to these questions.
The use of receipts to measure household food purchases has methodological limitations, including lack of information about the completeness of the receipts to represent all food purchases during the time interval covered [
5,
7,
23]. No objective measure exists of the true total number of receipts that participants should turn in to the research staff. Thus, it is not known whether participants turned in 100, 50% or some other portion of their total food purchase receipts. It is possible that participants may have omitted receipts for small purchases such as a single drink or candy item [
5,
7]. By contrast, a strength of the receipt data is its potentially lower reactivity than self-report assessments. It is an objective measure of food purchases, does not rely on participant memory, and may be less affected by social desirability responding. The enrolled sample was comprised of volunteers, and this could affect the generalizability of the results reported here.
Lower quality food purchasing among lower-income households may be due to higher food prices for higher quality foods [
3,
21‐
25]. Even within lower-income households, higher quality food purchases are associated with spending more money on those particular food categories [
3,
24]. Household configuration and the presence and number of children, and employment-related variables, including number of jobs and hours worked, may also influence the quality of foods and beverages purchased. Future research should examine the influence of these variables on the quality of household food and beverage purchases using large cohorts that will enable adequately powered analysis of these demographic and household variables.