Obesity is a major public health issue in the USA, and its prevalence continues to rise(Reference Rosenthal, Morton and Brethauer1). Obesity is linked to greater risk of various cancers, CVD and type 2 diabetes mellitus(Reference Guh, Zhang and Bansback2). Inadequate intake of fruits and vegetables (FV) is associated with higher risk of obesity and other diet-related chronic diseases such as heart disease and cancer(3–Reference Schwingshackl and Hoffmann8). Furthermore, while the variety of FV consumed is known to support good health(3,Reference Schwingshackl and Hoffmann8) , the USA population, on average, consumes few varieties of FV(3,9) . Rural populations and racially/ethnically diverse populations have disproportionate rates of chronic diseases and obesity, with low FV intake cited as a contributing factor(Reference Trivedi, Liu and Probst10–Reference Moore and Diez Roux12).
Evidence suggests that diet-related health disparities may be, in part, due to negative aspects of community food environments(Reference Bodor, Rice and Farley13,Reference Morland, Diez Roux and Wing14) . Access to healthy food sources, such as supermarkets and farmers’ markets, has been inversely associated with obesity, whereas the presence of convenience stores and fast food restaurants has been associated with an increased prevalence of obesity(Reference Bodor, Rice and Farley13,Reference Morland, Diez Roux and Wing14) . Limited evidence suggests that greater access to and use of farmers’ markets are associated with greater self-reported intake of FV(Reference Wheeler and Chapman-Novakofski15–Reference Jilcott Pitts, Hinkley and Wu18). Additionally, greater overall financial expenditures on FV have been associated with lower mortality(Reference Lo, Chang and Wahlqvist19). In a study of Taiwanese older adults, during a 10-year follow-up period, individuals with the greatest level of FV expenditures, ranking in the fourth and fifth quintiles, had a significantly reduced mortality rate and mortality risk decreased by 12 % and 10 % for every NT $15 (∼$0·50 USD) increase in daily vegetable and fruit expenditures, respectively(Reference Lo, Chang and Wahlqvist19).
Most studies examining associations between shopping at farmers’ markets and FV intake have only used self-reported measures of FV intake, which may be subject to errors in recall, which can increase both random error and systematic bias which tends to overestimate consumption of healthier foods(Reference Dhurandhar, Schoeller and Brown20–Reference Livingstone and Black24). Thus, objective measures of FV intake are needed to accurately quantify intake and determine effectiveness of interventions and policies to improve dietary behaviours. Carotenoids are antioxidants that are found in high concentrations in yellow, orange, red and dark green FV, which deposit and accumulate in blood plasma and skin(Reference Saini, Nile and Park25). The current criterion standard for objective assessment of FV intake is measurement of carotenoids in blood plasma(26). However, collection, storage and analysis of blood plasma for assessment of carotenoids is invasive, time-consuming and resource-intensive. As an alternative, skin carotenoids measured with pressure-mediated reflection spectroscopy is a validated method to approximate FV intake(Reference Ermakov, Ermakova and Sharifzadeh27–Reference Jahns, Johnson and Conrad29).
In this paper, we examined associations between self-reported and objectively measured FV intake and three measures of farmers’ market shopping behaviour: (1) monthly frequency of farmers’ market shopping; (2) variety of FV purchased on one market day and (3) money and/or benefits typically spent on FV at the farmers’ market/week, in both a rural population and a racially/ethnically diverse urban population. We hypothesised that FV intake, measured both by self-report and skin carotenoids, would be positively associated with shopping frequency at farmers’ markets, variety of FV purchased and money and/or benefits spent on FV.
This cross-sectional study used a convenience sample of farmers’ market shoppers identified through public intercept at ten farmers’ markets in six counties in rural eastern North Carolina (NC) and 7 farmers’ markets in New York City (NYC) from June to August 2019. Eligible participants were at least 18 years of age and able to speak English. The study purpose was explained to each prospective participant, after which they were given the opportunity to ask questions, and verbal consent was obtained by research staff. Participants received a canvas tote bag as compensation.
Farmers’ market shopping behaviours
Each participant completed a short, self-administered questionnaire (approximately 5–10 min.) electronically on a tablet device. If requested by the participant, the researcher would administer the questionnaire orally. Three farmers’ market shopping behaviours were assessed. Participants were asked ‘During the farmers’ market season, approximately how often do you purchase fruits or vegetables from the farmers’ market?’ Response options were never, less than once a month, once a month, every other week and once a week. This variable was coded numerically as 0, 0·5, 1, 2 and 4 times/month, respectively. Participants were asked ‘Which fruits and vegetables did you buy at today’s market?’ Participants responded by selecting from a list of 68 FV, including options to write in any FV that was not included in the list. The total number of FV purchased was used as a measure of FV variety. The questionnaire also asked, ‘When you go to a farmers’ market, how much money (cash and/or benefits) do you usually spend on fresh fruits and vegetables?’ Benefits were defined as federal food assistance benefits such as the Supplemental Nutrition Assistance Program and participants responded with a numeric value.
Self-reported fruit and vegetable intake
Self-reported fruit intake was assessed by asking participants ‘How much fruit (in cups) do you eat in an average day?’ Participants were provided examples of quantities of fruit that are approximately equal to one cup and prompted not to include fruit juice. Likewise, vegetable intake was assessed by asking participants ‘How many vegetables (in cups) do you eat in an average day?’ Participants were again provided examples of quantities of vegetables that are approximately equal to one cup and prompted not to include French fries. Response options were whole and half numbers from 0 to 6 cups. These two fruit and vegetable questions were adapted from the American Heart Association’s Life’s Simple 7 score(Reference Tomaselli, Harty and Horton30).
Skin carotenoid measurement
Skin carotenoid scores were assessed using pressure-mediated reflection spectroscopy (the ‘Veggie Meter®’, Longevity Link Corporation, Salt Lake City, UT, USA). The Veggie Meter® is a valid, non-invasive, objective approximation of FV intake(Reference Pitts, Jahns and Wu28). Participants provided finger scans three times, and the mean of which generated skin carotenoid scores. Skin carotenoid scores range from 0 to 800, with higher numbers indicating higher skin carotenoid levels and thus greater FV intake. This tool has been validated against plasma carotenoids in diverse populations with a correlation between plasma carotenoids and Veggie Meter® assessed skin carotenoid scores of r = 0·71, P < 0·0001(Reference Pitts, Jahns and Wu28). The Veggie Meter® has also been used among diverse New Zealanders with findings indicating positive correlations between skin carotenoid scores and FV intake(Reference Rush, Amoah and Diep31).
Participants reported height in feet and inches and weight in pounds as part of the questionnaire from which BMI was calculated. Participants also reported their age, sex, race, smoking status, education and household income.
Farmers’ market shoppers were characterised using descriptive statistics, including means and standard deviations for continuous variables and frequencies for categorical variables. Descriptive statistics were calculated for the pooled sample of farmers’ market shoppers and for NYC and NC separately. To test for significant differences between NYC and NC shoppers, χ 2 tests (for nominal variables), Wilcoxon rank sum tests (for ordinal variables) and t tests (for continuous variables) were used.
Linear regression models were used to estimate the unadjusted relationships between each shopping behaviour and each measure of FV intake separately. Then, multivariable regression models were used to control for age, sex, race, smoking status, education, household income and state. To account for clustering of responses within markets, multi-level models included a categorical farmers’ market variable as a random effect when there was enough variation across markets to make this computation possible, which was only the case for skin carotenoids. All models used age < 60 years, male, Caucasian, less than college graduate, household income < $40 000 and NYC as reference groups. Reference groups were chosen based on the median responses to demographic questions. The assumption of non-multicollinearity was tested by analysis of the variance inflation factor and tolerance of each model, and none suggested multicollinearity (variance inflation factor < 10, Tolerance > 0·2). FV purchase variety was not normally distributed (skewness = 3·6, kurtosis = 20·0, Shapiro–Wilk P < 0·001) and was log transformed and identical regressions performed as sensitivity analyses. Analysis was performed using SAS version 9.4 (SAS Institute Inc.). The α < 0·05 significance level was used to determine statistical significance.
We surveyed a total of 645 shoppers, in seven farmers’ markets in NYC (n 377) and ten farmers’ markets in rural NC (n 268). The number of participants surveyed in each market ranged from 1 to 95. Farmers’ market shoppers in this study were mostly female (79·2 %) and more fell into the age 60+ years (36·9 %) category than the other age categories. The shoppers surveyed in NC were relatively homogonous (70·2 % Caucasian, 22·8 % African American and 1·1 % Hispanic/Latino), while those in NYC were significantly more racially and ethnically diverse (23·1 % Caucasian, 30·5 % African American and 33·4 % Hispanic/Latino). Farmers’ market shoppers typically had a household income of at least $40 000 (52·7 %), about half were college graduates (52·6 %), few currently smoked (8·1 %) and mean BMI was 28·0 kg/m2. Age, race, ethnicity and BMI differed significantly between shoppers in NYC and rural NC: NC shoppers were older, less racially/ethnically diverse and had higher BMI than NYC shoppers (Table 1).
Significance at the α < 0·05 level indicated using boldface type.
On average, farmers’ market shoppers purchased FV at the farmers’ market approximately 2·5 times/month, spent $23·15 on FV each visit to the farmers’ market and purchased 2·7 different varieties of FV on the day of survey (Table 2). Compared with farmers’ market shoppers in rural NC, NYC shoppers purchased more varieties of FV (3·1 v. 2·3, P = 0·011) and spent more on FV at the farmers’ market ($24·88 v. $20·87, P = 0·035). On average, participants reported consuming 2·2 cups of fruits/d, 2·5 cups of vegetables/d and had a mean skin carotenoid score of 289·2. There was a significant difference in the mean skin carotenoid scores of NYC shoppers and NC shoppers (313·4 v. 254·1, P < 0·001) but no differences in self-reported fruit or vegetable intake.
FV, fruits and vegetables.
Significance at the α < 0·05 level indicated using boldface type.
There were positive, statistically significant associations between FV purchasing frequency (times/months) and self-reported fruit (P = 0·007) and vegetable intake (P < 0·001) and mean skin carotenoid scores (P = 0·009) in the adjusted models (Table 3). FV purchase variety was also positively associated with self-reported fruit intake (P = 0·002) and self-reported vegetable intake (P = 0·005), but not skin carotenoids, in the multivariate regression models. Sensitivity analyses using the log of FV variety produced results that were similar in direction and significance (data not shown). After adjustment, the amount of money typically spent on FV at a farmers’ market was positively associated with self-reported fruit intake (P < 0·001) and self-reported vegetable intake (P < 0·001), but not skin carotenoids. Adjustment for state was significant in models of objectively measured carotenoids, but not self-reported FV intake.
FV, fruits and vegetables.
Significance at the α < 0·05 level indicated using boldface type.
* Farmers’ market was included as a random effect in this model to account for clustering.
In the current study, we found that frequency of shopping at farmers’ markets was positively associated with self-reported and objectively assessed FV intake in a diverse sample of farmers’ markets shoppers from two geographic areas – one urban (NYC) and one rural (NC). This is in agreement with prior studies which found that increased shopping at farmers’ markets is associated with greater FV intake(Reference Wheeler and Chapman-Novakofski15–Reference Jilcott Pitts, Hinkley and Wu18), yet adds to the current literature by demonstrating this cross-sectional association persists when FV intake is assessed by a valid, objective measure (skin carotenoids). We also found that the amount of money typically spent on FV purchases on each trip to the farmers’ market and the variety of FV purchased at the farmers’ market on the day of survey were positively associated with self-reported FV intake, but neither was associated with skin carotenoids. These seemingly contradictory findings may be because many of the vegetables sold at farmers’ markets, such as cucumbers, squash, onions and potatoes are low in carotenoids(32).
Our findings support the evidence that frequent farmers’ market shopping is associated with greater FV intake and adds data regarding two other relevant dimensions of the farmers’ market shopping experience (amount of money spent on FV at the farmers’ market and variety of FV purchased). Our findings are in agreement with others that have found that greater vegetable variety is associated with higher intake of vegetables(Reference Keim, Forester and Lyly33–Reference Parizel, Labouré and Marsset-Baglieri35).
This study also adds to the literature regarding expenditures at farmers’ markets: a Canadian study revealed that farmers’ market shoppers spent on average $5 CAD (∼$3·60 USD)/trip to the market v. $23/trip in our sample(Reference Rebouillat, Bonin and Kestens36). The mean variety of FV purchased in the Canadian study was similar to the mean variety in our study (2·8 v. 2·7)(Reference Rebouillat, Bonin and Kestens36). In addition, Freedman et al.(Reference Freedman, Flocke and Shon37) suggested that an approach that includes the establishment of farmers’ markets in low-income neighbourhoods, acceptance of federal food assistance benefits for payment and availability of healthy food incentive programming may increase purchasing at farmers’ markets among underserved populations. In the current paper, we examined cross-sectional associations between farmers’ market shopping behaviours and FV intake. We hypothesised that more intense shopping behaviours (greater frequency, variety and monetary value of FV purchased at farmers’ markets) would be positively associated with FV intake. This hypothesis was supported, suggesting that research should test the relative effectiveness of programmes to increase farmers’ market shopping intensity (e.g. double-up bucks, variety incentives, return visitor incentives) in addition to mechanisms that simply incentivise initial farmers’ market attendance (e.g. first time shopper coupons, introduction coupons).
Interestingly, there were significant state-level differences in mean skin carotenoid scores, an objective measure of FV intake, with urban NYC shoppers having higher skin carotenoids than rural NC shoppers. This is in agreement with prior studies demonstrating differences in FV intake by rural/urban residence(Reference Trivedi, Liu and Probst10,Reference Dean and Sharkey11) and should be examined in future studies.
Much of the literature on farmers’ market shopping is among Caucasian, higher socio-economic status, females(Reference Byker, Shanks and Misyak38–Reference Elepu and Mazzocco40). The geographic and racial/ethnic variability of the sample is a key strength of this study, along with the assessment of three dimensions of farmers’ market shopping behaviour, and the use of an objective measure of FV intake (skin carotenoids) in addition to self-reported FV intake data. However, the study was limited by its cross-sectional design from which we could not infer causality between farmers’ market shopping behaviours and FV intake nor understand the direction of any potential links. Another limitation of this study is the possibility of measurement bias in self-reported data. Farmers’ market shopping behaviours and FV intake may be subject to potential overestimation of positive behaviour due to social desirability bias. Assessment of FV intake used questions from the widely employed American Heart Association’s Life’s Simple 7 questionnaire(Reference Tomaselli, Harty and Horton30) to reduce this potential for bias. It is also possible that skin carotenoid scores were influenced by environmental factors. Smoking status is known to be associated with skin carotenoids and was controlled for in adjusted models, but other environmental factors such as secondhand smoke in the home were not available(Reference Moran, Mohn and Hason41). Additionally, the measure of FV variety was not divided into smaller groupings of FV, some of which may be carotenoid rich, while others are not a significant source of carotenoids. This may have confounded potential associations between FV variety and skin carotenoids. Finally, generalisability is limited based upon the use of convenience samples in rural NC and urban NYC.
The current study contributes important findings related to shopping behaviours and spending at farmers’ markets and their positive relationships with FV intake among shoppers. Further research is needed to test causality between farmers’ market shopping behaviours and FV intake and to test the relative effectiveness of programs to increase farmers’ market shopping intensity in addition to farmers’ market introductions, in order to effectively promote FV intake in a variety of community food environments.
Acknowledgements: We would like to acknowledge Simran Malhotra, Zoe Bertol-Foell, Ciara Roche and Adhirai Muthukumar, Nevin Johnson, Victoria Edwards Donadio and others who collected data for the study. Financial support: This research was supported by an Engaged Undergraduate Research Grant from Cornell University and the East Carolina University Department of Public Health. Conflicts of interest: There are no conflicts of interest. Authorship: C.J.K., S.B.J.P., L.C.V., K.L.H. and R.S.F. conceived of the study. L.C.V., K.L.H., A.R., R.S.F. and S.B.J.P. collaborated on questionnaire design and development. C.J.K., L.C.V., R.S.F. and S.B.J.P. supervised data collection. C.J.K. and G.M. completed statistical analyses, guided by K.L.H. C.J.K. drafted the manuscript, with guidance from S.B.J.P. and K.L.H., with revision from L.C.V. and G.M. All authors reviewed and approved the manuscript as submitted. Ethics of human subject participation: This study was conducted according to the guidelines laid down in the Declaration of Helsinki, and all procedures involving research study participants were approved by the Institutional Review Boards at Cornell University (IRB# 1806008085) and East Carolina University (IRB# 19-001223). Verbal informed consent was obtained from all subjects. Verbal consent was witnessed and formally recorded.
For supplementary material accompanying this paper visit https://doi.org/10.1017/S1368980021004602