The effects of a 25% discount on fruits and vegetables: results of a randomized trial in a three-dimensional web-based supermarket

The effects of nudging and pricing strategies on the availability and purchases of ultra-processed foods: A secondary analysis of the Supreme Nudge trial

Regular consumption of ultra-processed foods (UPF) is a risk factor for morbidity and mortality. UPF are widely available in supermarkets. Nudging and pricing strategies are promising strategies to promote healthier supermarket purchases and may reduce UPF purchases. We investigated whether supermarket nudging and pricing strategies targeting healthy foods, but not specifically discouraging UPF, would change UPF availability, price, promotion and placement (UPF-APPP) in supermarkets and customer UPF purchases. We used data from the Supreme Nudge parallel cluster-randomized controlled trial, testing the effect of a combined nudging and pricing intervention promoting healthy products. The Dutch Consumer Food Environment Score (D-CFES) was used to audit 12 participating supermarkets in terms of UPF-APPP. We used customer loyalty card data of the first twelve intervention weeks from 321 participants to calculate the proportion of UPF purchases. Descriptive statistics were used to assess differences in D-CFES between supermarkets. Mixed model analyses were used to assess the association between the D-CFES and UPF purchases and the effect of the intervention on UPF purchases. No difference in the D-CFES between intervention and control supermarkets were found. No statistically significant association between the D-CFES and UPF purchases (β = -0.00, 95%CI: -0.02, 0.01) and no significant effect of the intervention on UPF purchases (β = 0.02, 95%CI: -0.07, 0.12) was observed. Given the significant proportion of unhealthy and UPF products in Dutch supermarkets, nudging and pricing strategies aimed at promoting healthy food purchases are not sufficient for reducing UPF-APPP nor purchases, and nationwide regulation may be needed.Trial registration number: Dutch Trial Register ID NL7064, May 30, 2018, https://trialsearch.who.int/Trial2.aspx?TrialID=NTR7302.

Every step you take: Nudging animal welfare product purchases in a virtual supermarket

Animal welfare (AW) is a growing concern for consumers in Germany; however, not all consumers regularly purchase products that have been produced according to high AW standards. The goal of the present study is to test the effect of a multilayered nudge to increase the availability and improve the visibility of AW products in a 3D online virtual supermarket (VS). The nudge included a shelf with AW products (referred to as AW shelf) which was made visible through banners and footsteps on the floor of the VS. The sample of this pre-registered experiment consisted of n = 374 German consumers who regularly purchase meat, milk, and eggs. The results demonstrated that the multilayered nudge was highly effective: the percentage of AW products purchased in the nudging condition was almost twice as high as in the control group. Furthermore, we investigated variables that mediate (ease of finding AW products in the VS) and moderate (price sensitivity) the effectiveness of the multilayered nudge, but no evidence for an effect was obtained. We conclude that multilayered nudges may be a promising tool to increase consumers' AW product purchases. More research is needed to replicate this finding with a field study in a real supermarket.

A Commentary on the Healthy Community Stores Case Study Project: Implications for Retailers, Policy, and Future Research

In the United States, low-income, underserved rural and urban settings experience poor access to healthy, affordable food. Introducing new food outlets in these locations has shown mixed results for improving healthy food consumption. The Healthy Community Stores Case Study Project (HCSCSP) explored an alternative strategy: supporting mission-driven, locally owned, healthy community food stores to improve healthy food access. The HCSCSP used a multiple case study approach, and conducted a cross-case analysis of seven urban healthy food stores across the United States. The main purpose of this commentary paper is to summarize the main practice strategies for stores as well as future directions for researchers and policy-makers based on results from the prior cross-case analyses. We organize these strategies using key concepts from the Retail Food Environment and Customer Interaction Model. Several key strategies for store success are presented including the use of non-traditional business models, focus on specific retail actors such as store champions and multiple vendor relationships, and a stores' role in the broader community context, as well as the striking challenges faced across store locations. Further exploration of these store strategies and how they are implemented is needed, and may inform policies that can support these types of healthy retail sites and sustain their efforts in improving healthy food access in their communities.

2022 Prevention of chronic non-communicable diseases in Of the Russian Federation. National guidelines

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Are nudging and pricing strategies on food purchasing behaviors equally effective for all? Secondary analyses from the Supreme Nudge virtual supermarket study

Nudging and pricing strategies are effective in promoting healthier purchases. However, whether the effects are equal across individuals with different personal characteristics is unknown. This exploratory study aimed to examine differential effects of nudging and pricing strategies on food purchases across individuals' levels of impulsivity, price sensitivity, decision-making styles, and food choice motives. Data from a virtual supermarket experiment where participants were exposed to five study conditions (control, nudging, pricing, salient pricing, and salient pricing with nudging) was used. Participants completed questionnaires assessing their impulsivity, price sensitivity, decision-making styles, and food choice motives. The outcome was the percentage of healthy food purchases. Effect modification was analyzed by adding interaction terms to the statistical models and post-hoc probing was conducted for statistically significant interaction terms. We used data from 400 Dutch adult participants (61.3% female, median age 30.0 years (IQR 24.0)). The effects of the nudging and pricing conditions on healthy food purchases were not modified by impulsivity, price sensitivity, decision-making styles, and the food choice motives 'health' and 'price'. Only the interactions of the food choice motive 'natural content of foods' x pricing (B = -1.02, 90%CI = -2.04; -0.01), the food choice motive 'weight control' x nudging (B = -2.15, 90%CI = -3.34; -0.95), and 'weight control' x pricing (B = -1.87, 90%CI = -3.11; -0.62) were statistically significant. Post-hoc probing indicated that nudging and/or pricing strategies were more effective in individuals who gave lower priority to these food choice motives. The effects of nudging and pricing strategies on increasing healthy food purchasing behaviors, at least in a virtual environment, do not seem to be influenced by personal characteristics and may therefore be implemented as general health promoting strategies.

Helping parents provide vegetable snacks: Investigating price and taste as barriers

Snacks contribute nearly one-quarter of children's daily energy intake in the USA. Snack time therefore represents an opportunity for parents to provide foods with key nutrients. Instead, the most common snack foods are major contributors to children's consumption of added sugars and sodium. Parents face major barriers to providing healthier snacks, including perceptions of high cost and lack of child acceptance. We obtained both economic and qualitative data to inform and optimize interventions for parents to promote vegetable snacks for children. We conducted a survey with parents (n = 368) to estimate how much of a discount would influence vegetable snack purchases by estimating willingness-to-pay using the contingent valuation method, using baby-cut carrots as a sample product. We conducted three focus groups (n = 19) and 1 group interview (n = 2) with children to help understand how to increase the appeal of vegetable snacks. Most (70%) parents accepted the reference price for the vegetable snack. Among those who did not, contingent valuation analysis revealed that a mean discount of approximately 30% would shift consumers to purchasing the snack. Focus group results revealed that the appeal of vegetable snacks to children was influenced by how they were prepared and presented, and the child's familiarity with the vegetables and ability to choose among them. This study lays the groundwork for effective interventions to promote the provision of vegetable snacks by parents.

The effects of nudging and pricing on healthy food purchasing behavior in a virtual supermarket setting: a randomized experiment

BACKGROUND

Evidence on what strategies - or combination of strategies - are most effective and equitable in promoting healthier diets is needed. This study examined the efficacy of nudging and pricing strategies on increasing healthy food purchases and the potential differential effect by socio-economic position (SEP) among Dutch adults in a virtual supermarket.

METHODS

A randomized study design was conducted within a virtual supermarket (SN VirtuMart). Participants were exposed to five within-subject study conditions (control, nudging, pricing, price salience and price salience with nudging) and randomized to one of three between-subject study arms (a 25% price increase on unhealthy products, a 25% discount on healthy products, or a 25% price increase and discount). In total, 455 participants of low and high SEP (using either education or income as proxy) were randomized to conduct their weekly shopping in a virtual supermarket for five consecutive weeks. The primary outcome included the percentage of healthy purchases. Data were analyzed using linear mixed models.

RESULTS

In total, 346 (76%) adults completed all five shops within the SN VirtuMart. Median age was 32.5, 49.2% had high education and 32.8% had high income. Out of the 12 conditions, four conditions were statistically significantly different from the control condition. Nudging and non-salient pricing strategies alone did not statistically significantly increase healthy food purchases, whereas a combination of salient price increases and discounts led to an increase in the percentage of healthy food purchases (B 4.5, 95%CI 2.6; 6.4). Combining salient pricing and nudging strategies led to increases in the percentage of healthy products in all three pricing arms, with largest effects found in the combined price increase and discount arm (B = 4.0, 95%CI = 2.0; 6.0). Effects were not modified by SEP.

CONCLUSIONS

Combining health-related price increases and discounts and combining these salient pricing strategies with nudges in a supermarket setting seems to stimulate healthy food purchases for both low and high SEP populations. However, further research in real-world settings is needed.

TRIAL REGISTRATION

This randomized trial ( NTR7293 ) was registered in the Dutch trial registry ( www.trialregister.nl ).

Potassium Intake in India: Opportunity for Mitigating Risks of High-Sodium Diets

INTRODUCTION

Most Indians are vegetarian or eat very little meat, which could imply high potassium intake. Because a high-potassium diet could counterbalance the adverse health effects of high-sodium intake, this study aimed to describe potassium relative to sodium intake and investigate the relationship between blood pressure and potassium intake relative to sodium intake in rural and urban India.

METHODS

Investigators collected 24-hour urines from 1,445 participants in a subset of 2 population-based surveys in North India in 2012-2013. Standardized questionnaires were used to collect information on demography, behaviors (tobacco, alcohol consumption, physical activity, and diet [food frequency and 24-hour recall]), and medical history. After evaluating expected versus measured creatinine excretion, the authors calculated median urine potassium excretion and sodium/potassium ratio, according to sex and urban or rural residence, and estimated least square means for the urine measures by participant demographics and comorbidities, after accounting for caloric intake. Two-year blood pressure follow-up data were available in the urban study, and ANCOVA regression was used to determine the association with urine measures. All the statistical analyses of the data were done in January 2019.

RESULTS

Acceptable 24-hour urine collections were available in 1,397 participants (rural, n=730). Median urine potassium excretions were 1,492 (IQR=1,012-2,063) and 975 (615-1,497) mg/day; sodium/potassium ratios met the recommended target of <1 in 2.9% rural and 6.6% urban participants. Rural participants did not have higher potassium or lower (better) sodium/potassium ratios when diagnosed with hypertension or other cardiovascular conditions. Higher potassium excretion was associated with lower blood pressure during follow-up among the urban participants (mean systolic blood pressure, 129 vs 133 mm Hg in highest vs lowest potassium excretion tertiles; p=0.029).

CONCLUSIONS

Low potassium intake in India warrants dietary policies promoting intake of potassium-rich foods to improve heart health. This approach may be more acceptable than programs focused on sodium reduction alone.

DEBATE: Do interventions based on behavioral theory work in the real world?

BACKGROUND

Behavioral scientists suggest that for behavior change interventions to work effectively, and deliver population-level health outcomes, they must be underpinned by behavioral theory. However, despite implementation of such interventions, population levels of both health outcomes and linked behaviors have remained relatively static. We debate the extent to which interventions based on behavioral theory work in the real world to address population health outcomes.

DISCUSSION

Hagger argues there is substantive evidence supporting the efficacy and effectiveness of interventions based on behavioral theory in promoting population-level health behavior change in the 'real world'. However, large-scale effectiveness trials within existing networks are relatively scarce, and more are needed leveraging insights from implementation science. Importantly, sustained investment in effective behavioral interventions is needed, and behavioral scientists should engage in greater advocacy to persuade gatekeepers to invest in behavioral interventions. Weed argues there is no evidence to demonstrate behavioral theory interventions are genuinely effective in real world settings in populations that are offered them: they are merely efficacious for those that receive them. Despite behavioral volatility that is a normal part of maintaining steady-state population behavior levels creating the illusion of effectiveness, interventions fail in shifting the curve of population behaviors because they focus on individuals rather than populations. Hagger responds that behavioral interventions work in the 'real world' in spite of, not because of, flux in health behaviors, and that the contention that behavioral theory focuses solely on individual behavior change is inaccurate. Weed responds that the focus on extending the controls of efficacy trials into implementation is impractical, uneconomic and futile, and this has squandered opportunities to conduct genuine effectiveness trials in naturalistic settings. Hagger contends that interventions based on behavioral theory are effective in changing population-level behavior in 'real world' contexts, but more evidence on how best to implement them and how to engage policymakers and practitioners to provide sustained funding is needed. Weed argues for a paradigm shift, away from aggregative attempts to effect individual behavior change towards a focus on disrupting social practices, underpinned by understanding social and economic causation of the distribution and acceptance of behaviors in a population.

The Association Between Food Prices and the Blood Glucose Level of US Adults With Type 2 Diabetes

Objectives. We estimated the association between the price of healthy and less-healthy food groups and blood sugar among US adults with type 2 diabetes.

Methods. We linked 1999–2006 National Health and Nutrition Examination Survey health information to food prices contained in the Quarterly Food-at-Home Price Database. We regressed blood sugar levels on food prices from the previous calendar quarter, controlling for market region and a range of other covariates. We also examined whether the association between food prices and blood sugar varies among different income groups.

Results. The prices of produce and low-fat dairy foods were associated with blood sugar levels of people with type 2 diabetes. Specifically, higher prices for produce and low-fat dairy foods were associated with higher levels of glycated hemoglobin and fasting plasma glucose 3 months later. Food prices had a greater association with blood sugar for low-income people than for higher-income people, and in the expected direction.

Conclusions. Higher prices of healthy foods were associated with increased blood sugar among people with type 2 diabetes. The association was especially pronounced among low-income people with type 2 diabetes.

Appraisal of short and long versions of the Nutrition Environment Measures Survey (NEMS-S and NEMS-R) in Australia

OBJECTIVE

Research has begun to take a more ecological view of eating behaviour, examining multiple levels of influence: personal, social and environmental. The food environment is a major influence on eating behaviour, attracting the attention of researchers who have measured it in a number of ways. The present paper examines the short-form version, in comparison to the long-form version, of the Nutrition Environment Measures Survey (NEMS) - an observational food outlet audit tool.

DESIGN

Both the short-form and long-form were examined to qualitatively appraise the dimensions of the food environment assessed by each measure. Data from 135 food outlets in Australia were then used to compare results obtained using the short-form with the results from the long-form method, to consider the utility of the short-form measure.

SETTING

The retail food environment in Australia.ParticipantsOne hundred and thirty-five food outlets in Australia.

RESULTS

Results indicate that the short-form predominantly assessed availability of healthful foods (one aspect of the food environment). Several critical dimensions of the food environment known to influence eating behaviour were not assessed. For this data set, the short-form produced scores inconsistent with the longer version of the measure, delivering inflated estimates for stores and deflated estimates for restaurants.

CONCLUSIONS

Scores between the long-form and short-form versions were not comparable in this Australian study. Further development of food environment measures is recommended and must balance instrument brevity with the need to accurately capture important aspects of the food environment known to influence eating behaviour.

Grocery store interventions to change food purchasing behaviors: a systematic review of randomized controlled trials

Background

Diet is an important determinant of health, and food purchasing is a key antecedent to consumption.

Objective

We set out to evaluate the effectiveness of grocery store interventions to change food purchasing, and to examine whether effectiveness varied based on intervention components, setting, or socioeconomic status.

Design

We conducted a systematic review of randomized controlled trials (search performed June 2017). Studies must have: aimed to change food purchasing; been implemented in grocery stores (real or simulated); reported purchasing; and had a minimal control or compared interventions fulfilling our criteria. Searching, screening, bias assessment, and data extraction followed Cochrane methods. We grouped studies by intervention type (economic, environmental, swaps, and/or education), synthesized results narratively, and conducted an exploratory qualitative comparative analysis.

Results

We included 35 studies representing 89 interventions, >20,000 participants, and >800 stores. Risk of bias was mixed. Economic interventions showed the most promise, with 8 of the 9 studies in real stores and all 6 in simulated environments detecting an effect on purchasing. Swap interventions appeared promising in the 2 studies based in real stores. Store environment interventions showed mixed effects. Education-only interventions appeared effective in simulated environments but not in real stores. Available data suggested that effects of economic interventions did not differ by socioeconomic status, whereas for other interventions impact was variable. In our qualitative comparative analysis, economic interventions (regardless of setting) and environmental and swap interventions in real stores were associated with statistically significant changes in purchasing in the desired direction for ≥1 of the foods targeted by the intervention, whereas education-only interventions in real stores were not.

Conclusions

Findings suggest that interventions implemented in grocery stores-particularly ones that manipulate price, suggest swaps, and perhaps manipulate item availability-have an impact on purchasing and could play a role in public health strategies to improve health. Review protocol registered at https://www.crd.york.ac.uk/PROSPERO/ as CRD42017068809.

Using a UK Virtual Supermarket to Examine Purchasing Behavior Across Different Income Groups in the United Kingdom: Development and Feasibility Study

BACKGROUND

The majority of food in the United Kingdom is purchased in supermarkets, and therefore, supermarket interventions provide an opportunity to improve diets. Randomized controlled trials are costly, time-consuming, and difficult to conduct in real stores. Alternative approaches of assessing the impact of supermarket interventions on food purchases are needed, especially with respect to assessing differential impacts on population subgroups.

OBJECTIVE

The aim of this study was to assess the feasibility of using the United Kingdom Virtual Supermarket (UKVS), a three-dimensional (3D) computer simulation of a supermarket, to measure food purchasing behavior across income groups.

METHODS

Participants (primary household shoppers in the United Kingdom with computer access) were asked to conduct two shopping tasks using the UKVS and complete questionnaires on demographics, food purchasing habits, and feedback on the UKVS software. Data on recruitment method and rate, completion of study procedure, purchases, and feedback on usability were collected to inform future trial protocols.

RESULTS

A total of 98 participants were recruited, and 46 (47%) fully completed the study procedure. Low-income participants were less likely to complete the study (P=.02). Most participants found the UKVS easy to use (38/46, 83%) and reported that UKVS purchases resembled their usual purchases (41/46, 89%).

CONCLUSIONS

The UKVS is likely to be a useful tool to examine the effects of nutrition interventions using randomized controlled designs. Feedback was positive from participants who completed the study and did not differ by income group. However, retention was low and needs to be addressed in future studies. This study provides purchasing data to establish sample size requirements for full trials using the UKVS.

Using a Virtual Store As a Research Tool to Investigate Consumer In-store Behavior

People's responses to products and/or choice environments are crucial to understanding in-store consumer behaviors. Currently, there are various approaches (e.g., surveys or laboratory settings) to study in-store behaviors, but the external validity of these is limited by their poor capability to resemble realistic choice environments. In addition, building a real store to meet experimental conditions while controlling for undesirable effects is costly and highly difficult. A virtual store developed by virtual reality techniques potentially transcends these limitations by offering the simulation of a 3D virtual store environment in a realistic, flexible, and cost-efficient way. In particular, a virtual store interactively allows consumers (participants) to experience and interact with objects in a tightly controlled yet realistic setting. This paper presents the key elements of using a desktop virtual store to study in-store consumer behavior. Descriptions of the protocol steps to: 1) build the experimental store, 2) prepare the data management program, 3) run the virtual store experiment, and 4) organize and export data from the data management program are presented. The virtual store enables participants to navigate through the store, choose a product from alternatives, and select or return products. Moreover, consumer-related shopping behaviors (e.g., shopping time, walking speed, and number and type of products examined and bought) can also be collected. The protocol is illustrated with an example of a store layout experiment showing that shelf length and shelf orientation influence shopping- and movement-related behaviors. This demonstrates that the use of a virtual store facilitates the study of consumer responses. The virtual store can be especially helpful when examining factors that are costly or difficult to change in real life (e.g., overall store layout), products that are not presently available in the market, and routinized behaviors in familiar environments.

What is the effectiveness of obesity related interventions at retail grocery stores and supermarkets? -a systematic review

Background

The Prevalence of obesity and overweight has been increasing in many countries. Many factors have been identified as contributing to obesity including the food environment, especially the access, availability and affordability of healthy foods in grocery stores and supermarkets. Several interventions have been carried out in retail grocery/supermarket settings as part of an effort to understand and influence consumption of healthful foods. The review’s key outcome variable is sale/purchase of healthy foods as a result of the interventions. This systematic review sheds light on the effectiveness of food store interventions intended to promote the consumption of healthy foods and the methodological quality of studies reporting them.

Methods

Systematic literature search spanning from 2003 to 2015 (inclusive both years), and confined to papers in the English language was conducted. Studies fulfilling search criteria were identified and critically appraised. Studies included in this review report health interventions at physical food stores including supermarkets and corner stores, and with outcome variable of adopting healthier food purchasing/consumption behavior. The methodological quality of all included articles has been determined using a validated 16-item quality assessment tool (QATSDD).

Results

The literature search identified 1580 publications, of which 42 met the inclusion criteria. Most interventions used a combination of information (e.g. awareness raising through food labeling, promotions, campaigns, etc.) and increasing availability of healthy foods such as fruits and vegetables. Few used price interventions. The average quality score for all papers is 65.0%, or an overall medium methodological quality. Apart from few studies, most studies reported that store interventions were effective in promoting purchase of healthy foods.

Conclusion

Given the diverse study settings and despite the challenges of methodological quality for some papers, we find efficacy of in-store healthy food interventions in terms of increased purchase of healthy foods. Researchers need to take risk of bias and methodological quality into account when designing future studies that should guide policy makers. Interventions which combine price, information and easy access to and availability of healthy foods with interactive and engaging nutrition information, if carefully designed can help customers of food stores to buy and consume more healthy foods.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-016-3985-x) contains supplementary material, which is available to authorized users.

Preferred Healthy Food Nudges, Food Store Environments, and Customer Dietary Practices in 2 Low-Income Southern Communities

OBJECTIVE

To examine how food store environments can promote healthful eating, including (1) preferences for a variety of behavioral economics strategies to promote healthful food purchases, and (2) the cross-sectional association between the primary food store where participants reported shopping, dietary behaviors, and body mass index.

METHODS

Intercept survey participants (n = 342) from 2 midsized eastern North Carolina communities completed questionnaires regarding preferred behavioral economics strategies, the primary food store at which they shopped, and consumption of fruits, vegetables, and sugary beverages.

RESULTS

Frequently selected behavioral economic strategies included: (1) a token and reward system for fruit and vegetable purchases; and (2) price discounts on healthful foods and beverages. There was a significant association between the primary food store and consumption of fruits and vegetables (P = .005) and sugary beverages (P = .02).

CONCLUSIONS AND IMPLICATIONS

Future studies should examine associations between elements of the in-store food environment, purchases, and consumption.

Effects of Subsidies and Prohibitions on Nutrition in a Food Benefit Program: A Randomized Clinical Trial

IMPORTANCE

Strategies to improve the nutritional status of those participating in the Supplemental Nutrition Assistance Program (SNAP) are of interest to policymakers.

OBJECTIVE

To evaluate whether the proposed policy of incentivizing the purchase of fruits and vegetables and prohibiting the purchase of less nutritious foods in a food benefit program improves the nutritional quality of participants' diets.

DESIGN, SETTING, AND PARTICIPANTS

Lower income participants (n = 279) not currently enrolled in SNAP were randomized to 1 of 4 experimental financial food benefit conditions: (1) incentive (30% financial incentive for fruits and vegetables purchased using food benefits); (2) restriction (not allowed to buy sugar sweetened beverages, sweet baked goods, or candies with food benefits); (3) incentive plus restriction (30% financial incentive on fruits and vegetables and restriction of purchase of sugar sweetened beverages, sweet baked goods, or candy with food benefits); or (4) control (no incentive or restrictions on foods purchased with food benefits). Participants in all conditions were given a study-specific debit card where funds were added every 4 weeks for a 12-week period. Outcome measures were collected at baseline and in the final 4 weeks of the experimental period.

MAIN OUTCOMES AND MEASURES

Primary outcomes (from 24-hour dietary recalls) included intake of energy, discretionary calories, and overall diet quality.

RESULTS

A number of favorable changes were observed in the incentive plus restriction condition that were significantly different from changes in the control condition. These included (1) reduced intake of energy (-96 kcal/d, standard error [SE], 59.9); (2) reduced intake of discretionary calories (-64 kcal/d, SE 26.3); (3) reduced intake of sugar sweetened beverages, sweet baked goods, and candies (-0.6 servings/d, SE 0.2); (4) increased intake of solid fruit (0.2 servings/d, SE 0.1); and (5) improved Healthy Eating Index score (4.1 points, SE 1.4). Fewer improvements were observed in the incentive only and restriction only arms.

CONCLUSIONS AND RELEVANCE

A food benefit program that pairs incentives for purchasing more fruits and vegetables with restrictions on the purchase of less nutritious foods may reduce energy intake and improve the nutritional quality of the diet of participants compared with a program that does not include incentives or restrictions.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT02643576.

Contribution of food prices and diet cost to socioeconomic disparities in diet quality and health: a systematic review and analysis

CONTEXT

It is well established in the literature that healthier diets cost more than unhealthy diets.

OBJECTIVE

The aim of this review was to examine the contribution of food prices and diet cost to socioeconomic inequalities in diet quality.

DATA SOURCES

A systematic literature search of the PubMed, Google Scholar, and Web of Science databases was performed.

STUDY SELECTION

Publications linking food prices, dietary quality, and socioeconomic status were selected.

DATA EXTRACTION

Where possible, review conclusions were illustrated using a French national database of commonly consumed foods and their mean retail prices.

DATA SYNTHESIS

Foods of lower nutritional value and lower-quality diets generally cost less per calorie and tended to be selected by groups of lower socioeconomic status. A number of nutrient-dense foods were available at low cost but were not always palatable or culturally acceptable to the low-income consumer. Acceptable healthier diets were uniformly associated with higher costs. Food budgets in poverty were insufficient to ensure optimum diets.

CONCLUSIONS

Socioeconomic disparities in diet quality may be explained by the higher cost of healthy diets. Identifying food patterns that are nutrient rich, affordable, and appealing should be a priority to fight social inequalities in nutrition and health.

Differential Responses to Food Price Changes by Personal Characteristic: A Systematic Review of Experimental Studies

BACKGROUND

Fiscal interventions to improve population diet have been recommended for consideration by many organisations including the World Health Organisation and the United Nations and policies such as sugar-sweetened beverage taxes have been implemented at national and sub-national levels. However, concerns have been raised with respect to the differential impact of fiscal interventions on population sub-groups and this remains a barrier to implementation.

OBJECTIVE

To examine how personal characteristics (such as socioeconomic status, sex, impulsivity, and income) moderate changes in purchases of targeted foods in response to food and beverage price changes in experimental settings.

DESIGN

Systematic review.

DATA SOURCES

Online databases (PubMed, EMBASE, Web of Science, EconLit and PsycInfo), reference lists of previous reviews, and additional data from study authors.

STUDY SELECTION

We included randomised controlled trials where food and beverage prices were manipulated and reported differential effects of the intervention on participant sub-groups defined according to personal characteristics.

DATA ANALYSIS

Where possible, we extracted data to enable the calculation of price elasticities for the target foods by personal characteristic.

RESULTS

8 studies were included in the review. Across studies, the difference in price elasticity varied from 0.02 to 2.43 between groups within the same study. 11 out of the total of 18 comparisons of own-price elasticity estimates by personal characteristic differed by more than 0.2 between groups. Income related factors were the most commonly considered and there was an indication that own-price elasticity estimates do vary by income but the direction of this effect was not clear.

CONCLUSION

Experimental studies provide an opportunity to examine the differential effects of fiscal measures to improve population diets. Patterns in price sensitivity by personal characteristics are complex. General conclusions pertaining to the effects of personal characteristics on price sensitivity are not supported by the evidence, which shows heterogeneity between studies and populations.

TRIAL REGISTRATION

PROSPERO CRD42014009705.

Experimental analysis of the effect of taxes and subsides on calories purchased in an on-line supermarket

Taxes and subsidies are a public health approach to improving nutrient quality of food purchases. While taxes or subsidies influence purchasing, it is unclear whether they influence total energy or overall diet quality of foods purchased. Using a within subjects design, selected low nutrient dense foods (e.g. sweetened beverages, candy, salty snacks) were taxed, and fruits and vegetables and bottled water were subsidized by 12.5% or 25% in comparison to a usual price condition for 199 female shoppers in an experimental store. Results showed taxes reduced calories purchased of taxed foods (coefficient = -6.61, CI = -11.94 to -1.28) and subsidies increased calories purchased of subsidized foods (coefficient = 13.74, CI = 8.51 to 18.97). However, no overall effect was observed on total calories purchased. Both taxes and subsidies were associated with a reduction in calories purchased for grains (taxes: coefficient = -6.58, CI = -11.91 to -1.24, subsidies: coefficient = -12.86, CI = -18.08 to -7.63) and subsidies were associated with a reduction in calories purchased for miscellaneous foods (coefficient = -7.40, CI = -12.62 to -2.17) (mostly fats, oils and sugars). Subsidies improved the nutrient quality of foods purchased (coefficient = 0.14, CI = 0.07 to 0.21). These results suggest that taxes and subsidies can influence energy purchased for products taxed or subsidized, but not total energy purchased. However, the improvement in nutrient quality with subsidies indicates that pricing can shift nutritional quality of foods purchased. Research is needed to evaluate if differential pricing strategies based on nutrient quality are associated with reduction in calories and improvement in nutrient quality of foods purchased.

Healthy or Unhealthy on Sale? A cross-sectional study on the proportion of healthy and unhealthy foods promoted through flyer advertising by supermarkets in the Netherlands

Background

It is generally assumed that supermarkets promote unhealthy foods more heavily than healthy foods. Promotional flyers could be an effective tool for encouraging healthier food choices; however, there is a lack of good-quality evidence on this topic. Therefore, the aim of this study was to determine the proportions of healthy and unhealthy foods on promotion in Dutch supermarket flyers.

Methods

Supermarket food promotions were assessed using the weekly promotional flyers of four major Dutch supermarkets over a period of eight weeks. All promotions were evaluated for healthiness,

price discount, minimum purchase amount, product category and promotion type. The level of healthiness consists of a ‘healthy’ group; products which have a positive effect on preventing chronic diseases and can be eaten every day. The ‘unhealthy’ group contain products which have adverse effects on the prevention of chronic diseases. Data were analysed using ANOVA, independent t-tests and chi-square tests.

Results

A total of 1,495 promotions were included in this study. There were more promotions in the unhealthy category; 70% of promotions were categorised as unhealthy. The price discount was greater for the healthy promotions (mean 29.5%, SD 12.1) than for the two categories of unhealthy promotions (23.7%, SD 10.8; 25.4%, SD 10.5, respectively), a tendency which was mainly due to discounts in the fruit and vegetables category. To obtain the advertised discount, a significantly higher number of products had to be purchased in the unhealthy category than in the healthier categories. Promotions in the category meat, poultry and fish category occurred frequently.

Compared to traditional supermarkets, discounter supermarkets had higher percentages of unhealthy food discounts, lower discount levels and lower minimum purchase amounts.

Conclusion

This research confirmed that unhealthy foods are more frequently advertised than healthier foods in Dutch supermarket flyers. Moreover, consumers had to buy more products to achieve the discount when the promotion was categorized as unhealthy, providing extra incentive for buying additional unhealthy products. Future research should explore the proportion of healthy and unhealthy food discounts in relation to supermarkets’ total product range, to determine if unhealthy products are over-represented in promotions or if there are more unhealthy products stocked in supermarkets overall. The findings of this study provide an important basis for future intervention and policy development aiming to achieve healthier supermarket environments.

Price promotions on healthier compared with less healthy foods: a hierarchical regression analysis of the impact on sales and social patterning of responses to promotions in Great Britain

BACKGROUND

There is a growing concern, but limited evidence, that price promotions contribute to a poor diet and the social patterning of diet-related disease.

OBJECTIVE

We examined the following questions: 1) Are less-healthy foods more likely to be promoted than healthier foods? 2) Are consumers more responsive to promotions on less-healthy products? 3) Are there socioeconomic differences in food purchases in response to price promotions?

DESIGN

With the use of hierarchical regression, we analyzed data on purchases of 11,323 products within 135 food and beverage categories from 26,986 households in Great Britain during 2010. Major supermarkets operated the same price promotions in all branches. The number of stores that offered price promotions on each product for each week was used to measure the frequency of price promotions. We assessed the healthiness of each product by using a nutrient profiling (NP) model.

RESULTS

A total of 6788 products (60%) were in healthier categories and 4535 products (40%) were in less-healthy categories. There was no significant gap in the frequency of promotion by the healthiness of products neither within nor between categories. However, after we controlled for the reference price, price discount rate, and brand-specific effects, the sales uplift arising from price promotions was larger in less-healthy than in healthier categories; a 1-SD point increase in the category mean NP score, implying the category becomes less healthy, was associated with an additional 7.7-percentage point increase in sales (from 27.3% to 35.0%; P < 0.01). The magnitude of the sales uplift from promotions was larger for higher-socioeconomic status (SES) groups than for lower ones (34.6% for the high-SES group, 28.1% for the middle-SES group, and 23.1% for the low-SES group). Finally, there was no significant SES gap in the absolute volume of purchases of less-healthy foods made on promotion.

CONCLUSION

Attempts to limit promotions on less-healthy foods could improve the population diet but would be unlikely to reduce health inequalities arising from poorer diets in low-socioeconomic groups.

Identifying the effects of environmental and policy change interventions on healthy eating

Obesity has been characterized as a disease. Strategies to change the incidence and prevalence of this disease include a focus on changing physical and social environments, over and above individual-level strategies, using a multilevel or systems approach. We focus our attention on evidence published between 2008 and 2013 on the effectiveness of interventions in nutrition environments, i.e., environmental interventions designed to influence the intake of healthful foods and amount of energy consumed. An overarching socioecological framework that has guided much of this research was used to characterize different types of environmental strategies. Intervention examples in each area of the framework are provided with a discussion of key findings and related conceptual and methodological issues. The emphasis in this review is on adults, but clearly this literature is only one part of the picture. Much research has been focused on child-specific interventions, including environmental interventions. Some evidence suggests effectiveness of policy-based or other types of interventions that aim to regulate or restructure environments to promote healthy dietary choices, and these strategies would apply to both children and adults. Opportunities to evaluate these policy changes in adults' social and physical environments are rare. Much of the existing research has been with children. As conceptual and methodological issues continue to be identified and resolved, we hope that future research in this domain will identify environmental strategies that can be included in intervention toolboxes to build healthy nutrition environments for both adults and children.

Socio-demographic and behavioural determinants of weight gain in the Swiss population

Background

In Switzerland, socio-demographic and behavioural factors are associated with obesity, but no study ever assessed their impact on weight gain using prospective data.

Methods

Data from 4,469 participants (53.0% women), aged 35 to 75 years at baseline and followed for 5.5 years. Weight gain was considered as a rate (kg/year) or as gaining ≥5 kg during the study period.

Results

Rate of weight gain was lower among participants who were older (mean ± standard deviation: 0.46 ± 0.92, 0.33 ± 0.88, 0.21 ± 0.86 and 0.06 ± 0.74 kg/year in participants aged [35-45], [45-55], [55–65] and [65+] years, respectively, P<0.001); physically active (0.27 ± 0.82 vs. 0.35 ± 0.95 kg/year for sedentary, P < 0.005) or living in couple (0.29 ± 0.84 vs. 0.35 ± 0.96 kg/year for living single, P < 0.05), and higher among current smokers (0.41 ± 0.97, 0.26 ± 0.84 and 0.29±0.85 kg/year for current, former and never smokers, respectively, p<0.001). These findings were further confirmed by multivariable analysis. Multivariable logistic regression showed that receiving social help, being a current smoker or obese increased the likelihood of gaining ≥5 Kg: Odds ratio (OR) and 95% confidence interval (CI) 1.43 (1.16-1.77); 1.63 (1.35-1.95) and 1.95 (1.57-2.43), respectively, while living in couple or being physically active decreased the risk: 0.73 (0.62-0.86) and 0.72 (0.62-0.83), respectively. No association was found between weight gain and gender, being born in Switzerland or education.

Conclusions

In Switzerland, financial difficulties (indicated by receiving social help) and current smoking were associated with increases in body weight over a 5 years follow-up. Living in couple, being older or physically active were protective against weight gain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-015-1451-9) contains supplementary material, which is available to authorized users.

Testing for baseline differences in randomized controlled trials: an unhealthy research behavior that is hard to eradicate

Background

According to the CONSORT statement, significance testing of baseline differences in randomized controlled trials should not be performed. In fact, this practice has been discouraged by numerous authors throughout the last forty years. During that time span, reporting of baseline differences has substantially decreased in the leading general medical journals. Our own experience in the field of nutrition behavior research however, is that co-authors, reviewers and even editors are still very persistent in their demand for these tests. The aim of this paper is therefore to negate this demand by providing clear evidence as to why testing for baseline differences between intervention groups statistically is superfluous and why such results should not be published.

Discussion

Testing for baseline differences is often propagated because of the belief that it shows whether randomization was successful and it identifies real or important differences between treatment arms that should be accounted for in the statistical analyses. Especially the latter argument is flawed, because it ignores the fact that the prognostic strength of a variable is also important when the interest is in adjustment for confounding. In addition, including prognostic variables as covariates can increase the precision of the effect estimate. This means that choosing covariates based on significance tests for baseline differences might lead to omissions of important covariates and, less importantly, to inclusion of irrelevant covariates in the analysis. We used data from four supermarket trials on the effects of pricing strategies on fruit and vegetables purchases, to show that results from fully adjusted analyses sometimes do appreciably differ from results from analyses adjusted for significant baseline differences only. We propose to adjust for known or anticipated important prognostic variables. These could or should be pre-specified in trial protocols. Subsequently, authors should report results from the fully adjusted as well as crude analyses, especially for dichotomous and time to event data.

Summary

Based on our arguments, which were illustrated by our findings, we propose that journals in and outside the field of nutrition behavior actively adopt the CONSORT 2010 statement on this topic by not publishing significance tests for baseline differences anymore.

The relation of potassium and sodium intakes to diet cost among U.S. adults

The 2010 Dietary Guidelines recommended that Americans increase potassium and decrease sodium intakes to reduce the burden of hypertension. One reason why so few Americans meet the recommended potassium or sodium goals may be perceived or actual food costs. This study explored the monetary costs associated with potassium and sodium intakes using national food prices and a representative sample of US adults. Dietary intake data from the 2001-2002 National Health and Nutrition Examination Survey were merged with a national food prices database. In a population of 4744 adults, the association between the energy-adjusted sodium and potassium intakes, and the sodium-to-potassium ratio (Na:K) and energy-adjusted diet cost was evaluated. Diets that were more potassium-rich or had lower Na:K ratios were associated with higher diet costs, while sodium intakes were not related to cost. The difference in diet cost between extreme quintiles of potassium intakes was $1.49 (95% confidence interval: 1.29, 1.69). A food-level analysis showed that beans, potatoes, coffee, milk, bananas, citrus juices and carrots are frequently consumed and low-cost sources of potassium. Based on existing dietary data and current American eating habits, a potassium-dense diet was associated with higher diet costs, while sodium was not. Price interventions may be an effective approach to improve potassium intakes and reduce the Na:K ratio of the diet. The present methods helped identify some alternative low-cost foods that were effective in increasing potassium intakes. The identification and promotion of lower-cost foods to help individuals meet targeted dietary recommendations could accompany future dietary guidelines.

A school based study of time trends in food habits and their relation to socio-economic status among Norwegian adolescents, 2001-2009

Background

In recent years, adolescents’ food habits have become a major source of concern, and substantial policy and intervention efforts have been made to influence adolescents to consume more fruit and vegetables and less sweets and soft drink. Particular attention has been devoted to the social gradient in food habits, aiming to reduce dietary inequality. However, few internationally published studies have evaluated trends in teenagers’ food habits, or investigated how dietary inequalities develop.

Methods

We used Norwegian cross-sectional data from the international Health Behaviour in School-Aged Children (HBSC) study, collected via three nationally representative and comparable questionnaire surveys in 2001, 2005 and 2009. Food habits were identified by students’ consumption of fruit, vegetables, sweets and sugar rich soft drink. Socio-economic status (SES) was measured with the Family Affluence Scale (FAS). Multilevel logistic regression was used to analyze the data.

Results

The analyses indicated an overall positive trend in food habits among adolescents in Norway. Students were more likely to consume fruit (OR 1.76, CI 1.61-1.92) and vegetables (OR 1.51, CI 1.37-1.66) daily in 2005 as compared to 2001, and were less likely to consume sweets (OR 0.58, CI 0.51-0.66 resp. OR 0.77, CI 0.67-0.90) and soft drink (OR 0.55, CI 0.49-0.62 resp. OR 0.84, CI 0.73-0.96) daily when comparing, respectively, 2005 with 2001 and 2009 with 2005. Across all survey years, students with higher SES were more likely to eat fruit (OR 1.47, CI 1.32-1.65) and vegetables (OR 1.40, CI 1.24-1.58) daily than did students with lower SES. Our analyses indicated that the socio-economic differences were stable in the period 2002 - 2010, with uniform improvement in fruit and vegetable consumption across all SES levels. No significant associations between SES and intake of sweets and sugar-added soft drink were found.

Conclusion

The study identifies an overall improvement in diet among adolescents over a period characterized by onset of as well as ongoing initiatives targeting young people’s food habits. However, the observed socio-economic gradient in fruit and vegetable consumption remained unchanged.

Food prices and food shopping decisions of black women

Identifying food pricing strategies to encourage purchases of lower-calorie food products may be particularly important for black Americans. Black children and adults have higher than average obesity prevalence and disproportionate exposure to food marketing environments in which high calorie foods are readily available and heavily promoted. The main objective of this study was to characterize effects of price on food purchases of black female household shoppers in conjunction with other key decision attributes (calorie content/healthfulness, package size, and convenience). Factorial discrete choice experiments were conducted with 65 low- and middle-/higher-income black women. The within-subject study design assessed responses to hypothetical scenarios for purchasing frozen vegetables, bread, chips, soda, fruit drinks, chicken, and cheese. Linear models were used to estimate the effects of price, calorie level (or healthfulness for bread), package size, and convenience on the propensity to purchase items. Moderating effects of demographic and personal characteristics were assessed. Compared with a price that was 35% lower, the regular price was associated with a lesser propensity to purchase foods in all categories (β = -0.33 to -0.82 points on a 1 to 5 scale). Other attributes, primarily calorie content/healthfulness, were more influential than price for four of seven foods. The moderating variable most often associated with propensity to pay the regular versus lower price was the reported use of nutrition labels. Price reductions alone may increase purchases of certain lower-calorie or more healthful foods by black female shoppers. In other cases, effects may depend on combining price changes with nutrition education or improvements in other valued attributes.

The association between food prices and the blood glucose level of US adults with type 2 diabetes

OBJECTIVES

We estimated the association between the price of healthy and less-healthy food groups and blood sugar among US adults with type 2 diabetes.

METHODS

We linked 1999-2006 National Health and Nutrition Examination Survey health information to food prices contained in the Quarterly Food-at-Home Price Database. We regressed blood sugar levels on food prices from the previous calendar quarter, controlling for market region and a range of other covariates. We also examined whether the association between food prices and blood sugar varies among different income groups.

RESULTS

The prices of produce and low-fat dairy foods were associated with blood sugar levels of people with type 2 diabetes. Specifically, higher prices for produce and low-fat dairy foods were associated with higher levels of glycated hemoglobin and fasting plasma glucose 3 months later. Food prices had a greater association with blood sugar for low-income people than for higher-income people, and in the expected direction.

CONCLUSIONS

Higher prices of healthy foods were associated with increased blood sugar among people with type 2 diabetes. The association was especially pronounced among low-income people with type 2 diabetes.

Monitoring the price and affordability of foods and diets globally

Food prices and food affordability are important determinants of food choices, obesity and non-communicable diseases. As governments around the world consider policies to promote the consumption of healthier foods, data on the relative price and affordability of foods, with a particular focus on the difference between 'less healthy' and 'healthy' foods and diets, are urgently needed. This paper briefly reviews past and current approaches to monitoring food prices, and identifies key issues affecting the development of practical tools and methods for food price data collection, analysis and reporting. A step-wise monitoring framework, including measurement indicators, is proposed. 'Minimal' data collection will assess the differential price of 'healthy' and 'less healthy' foods; 'expanded' monitoring will assess the differential price of 'healthy' and 'less healthy' diets; and the 'optimal' approach will also monitor food affordability, by taking into account household income. The monitoring of the price and affordability of 'healthy' and 'less healthy' foods and diets globally will provide robust data and benchmarks to inform economic and fiscal policy responses. Given the range of methodological, cultural and logistical challenges in this area, it is imperative that all aspects of the proposed monitoring framework are tested rigorously before implementation.

Understanding price elasticities to inform public health research and intervention studies: key issues

Pricing policies such as taxes and subsidies are important tools in preventing and controlling a range of threats to public health. This is particularly so in tobacco and alcohol control efforts and efforts to change dietary patterns and physical activity levels as a means of addressing increases in noncommunicable diseases. To understand the potential impact of pricing policies, it is critical to understand the nature of price elasticities for consumer products. For example, price elasticities are key parameters in models of any food tax or subsidy that aims to quantify health impacts and cost-effectiveness. We detail relevant terms and discuss key issues surrounding price elasticities to inform public health research and intervention studies.

Effectiveness of subsidies in promoting healthy food purchases and consumption: a review of field experiments

OBJECTIVE

To systematically review evidence from field interventions on the effectiveness of monetary subsidies in promoting healthier food purchases and consumption.

DESIGN

Keyword and reference searches were conducted in five electronic databases: Cochrane Library, EconLit, MEDLINE, PsycINFO and Web of Science. Studies were included based on the following criteria: (i) intervention: field experiments; (ii) population: adolescents 12–17 years old or adults 18 years and older; (iii) design: randomized controlled trials, cohort studies or pre–post studies; (iv) subsidy: price discounts or vouchers for healthier foods; (v) outcome: food purchases or consumption; (vi) period: 1990–2012; and (vii) language: English. Twenty-four articles on twenty distinct experiments were included with study quality assessed using predefined methodological criteria.

SETTING

Interventions were conducted in seven countries: the USA (n 14), Canada (n 1), France (n 1), Germany (n 1), Netherlands (n 1), South Africa (n 1) and the UK (n 1). Subsidies applied to different types of foods such as fruits, vegetables and low-fat snacks sold in supermarkets, cafeterias, vending machines, farmers’ markets or restaurants.

SUBJECTS

Interventions enrolled various population subgroups such as school/ university students, metropolitan transit workers and low-income women.

RESULTS

All but one study found subsidies on healthier foods to significantly increase the purchase and consumption of promoted products. Study limitations include small and convenience samples, short intervention and follow-up duration, and lack of cost-effectiveness and overall diet assessment.

CONCLUSIONS

Subsidizing healthier foods tends to be effective in modifying dietary behaviour. Future studies should examine its long-term effectiveness and cost-effectiveness at the population level and its impact on overall diet intake.

Price discounts significantly enhance fruit and vegetable purchases when combined with nutrition education: a randomized controlled supermarket trial

BACKGROUND

Reducing fruit and vegetable (F&V) prices is a frequently considered policy to improve dietary habits in the context of health promotion. However, evidence on the effectiveness of this intervention is limited.

OBJECTIVE

The objective was to examine the effects of a 50% price discount on F&Vs or nutrition education or a combination of both on supermarket purchases.

DESIGN

A 6-mo randomized controlled trial within Dutch supermarkets was conducted. Regular supermarket shoppers were randomly assigned to 1 of 4 conditions: 50% price discounts on F&Vs, nutrition education, 50% price discounts plus nutrition education, or no intervention. A total of 199 participants provided baseline data; 151 (76%) were included in the final analysis. F&V purchases were measured by using supermarket register receipts at baseline, at 1 mo after the start of the intervention, at 3 mo, at 6 mo (end of the intervention period), and 3 mo after the intervention ended (9 mo).

RESULTS

Adjusted multilevel models showed significantly higher F&V purchases (per household/2 wk) as a result of the price discount (+3.9 kg; 95% CI: 1.5, 6.3 kg) and the discount plus education intervention (+5.6 kg; 95% CI: 3.2, 7.9 kg) at 6 mo compared with control. Moreover, the percentage of participants who consumed recommended amounts of F&Vs (≥400 g/d) increased from 42.5% at baseline to 61.3% at 6 mo in both discount groups (P = 0.03). Education alone had no significant effect.

CONCLUSIONS

Discounting F&Vs is a promising intervention strategy because it resulted in substantially higher F&V purchases, and no adverse effects were observed. Therefore, pricing strategies form an important focus for future interventions or policy. However, the long-term effects and the ultimate health outcomes require further investigation. This trial was registered at the ISRCTN Trial Register as number ISRCTN56596945 and at the Dutch Trial Register (http://www.trialregister.nl/trialreg/index.asp) as number NL22568.029.08.

Introducing taxes, subsidies or both: the effects of various food pricing strategies in a web-based supermarket randomized trial

OBJECTIVE

Fiscal policies may form a solution in improving dietary intake. This study aimed to examine the effectiveness of varying taxing and subsiding schemes to stimulate healthier food purchases.

METHODS

A randomized controlled trial with three levels of price reduction on healthy foods (no; 25%; 50%)×three levels of price increase on unhealthy foods (5%; 10%; 25%) factorial design was used. 150 participants were randomized into one of nine conditions and were asked to purchase groceries at a web-based supermarket. Data were collected in the Netherlands in January-February 2010 and analyzed using analysis of covariance.

RESULTS

Subjects receiving 50% discount purchased significantly more healthy foods than subjects receiving no (mean difference=6.62 items, p<0.01) or 25% discount (mean difference=4.87 items, p<0.05). Moreover, these subjects purchased more vegetables (mean difference=821 g;p<0.05 compared to no discount). However, participants with the highest discount also purchased significantly more calories. No significant effects of the price increases on unhealthy foods were found.

CONCLUSION

Price decreases are effective in stimulating healthy food purchases, but the proportion of healthy foods remains unaffected. Price increases up to 25% on unhealthier products do not significantly affect food purchases. Future studies are important to validate these results in real supermarkets and across different countries.