Marlène Perignon

Christophe Dubois

Rozenn Gazan

Matthieu Maillot

Laurent Muller

Bernard Ruffieux

Hind Gaigi

Nicole Darmon
email: nicole.darmon@inra.fr

Co-construction and Evaluation of a Prevention Program for Improving the Nutritional Quality of Food Purchases at No Additional Cost in a Socioeconomically Disadvantaged Population

Keywords: Intervention, low-income, diet, nutritional quality, food purchasing behavior, 30

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

experimental economics; cost; food prices 31 32 Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on [START_REF] Smith | Minority recruitment and participation in health research[END_REF] in Current Developments in cdn.nutrition.org Downloaded from

Introduction

The diets of the most socially disadvantaged individuals in industrialized countries are characterized by low intakes of fruit and vegetables, and by an overall poorer nutritional quality [START_REF] Darmon | Does social class predict diet quality?[END_REF]. This is partly explained by the high price per calorie ratio of fruits and vegetables compared with that of high-fat high-sugar products [START_REF] Drewnowski | The economics of obesity: dietary energy density and energy cost[END_REF][START_REF] Maillot | Nutrient-dense food groups have high energy costs: An econometric approach to nutrient profiling[END_REF]. Socially disadvantaged individuals perceive food prices as a barrier to adopting healthier diets [START_REF] Beydoun | How do socio-economic status, perceived economic barriers and nutritional benefits affect quality of dietary intake among US adults?[END_REF][START_REF] Waterlander | Perceptions on the use of pricing strategies to stimulate healthy eating among residents of deprived neighbourhoods: a focus group study[END_REF]. It is especially important for these populations to develop strategies to achieve good nutritional quality with a small budget. An intervention targeting socially disadvantaged populations must take into account their actual beliefs and expectations. A co-construction approach is thus recommended, involving participants at each step of the intervention, in order to maximize its impact [START_REF] Peters | Outil de pilotage et d'analyse de l'efficacité attendue des interventions en promotion de la santé. Preffi 2.0. Guide explicatifs, les fondements de Preffi[END_REF][START_REF] Who | Interventions on diet and physical activity[END_REF].

It is more difficult to have a balanced diet with a low food budget [START_REF] Darmon | Contribution of food prices and diet cost to socioeconomic disparities in diet quality and health: a systematic review and analysis[END_REF], and a minimal food budget (estimated at around 3.5€/d.person in France) is strictly needed to design diets that are both nutritious and socially acceptable [START_REF] Darmon | Impact of a cost constraint on nutritionally adequate food choices for French women: an analysis by linear programming[END_REF][START_REF] Maillot | Are the lowest-cost healthful food plans culturally and socially acceptable?[END_REF]. When the food budget is low but above this critical threshold, designing a balanced diet involves favoring a selection of foods with good nutritional quality for their price [START_REF] Maillot | Nutrient profiling can help identify foods of good nutritional quality for their price: a validation study with linear programming[END_REF]. Additionally, for a given food product, replacing national brands by generic products can lower cost without impairing nutritional quality.

Branded products have been found to be up to four times more costly than generic products with equivalent nutritional contents [START_REF] Cooper | Economy" line foods from four supermarkets and brand name equivalents: a comparison of their nutrient contents and costs[END_REF][START_REF] Darmon | Low-cost foods: how do they compare with their brand name equivalents? A French study[END_REF].

Experimental economics is a powerful methodology for evaluating the impact of a public policy. The principle is to bring participants revealing their real choices by using incentivecompatible mechanisms [START_REF] Harrison | Making Choice Studies Incentive Compatible[END_REF]. In nutrition, experimental economics has been used for ex ante evaluations of policies such as taxes and subsidies or nutritional labeling systems [START_REF] Darmon | Food price policies improve diet quality while increasing socioeconomic inequalities in nutrition[END_REF][START_REF] Crosetto | Helping consumers with a front-of-pack label: Numbers or colors?[END_REF][START_REF] Muller | Modification des achats en réponse à l'apposition de différents logos d'évaluation nutritionnelle sur la face avant des emballages[END_REF][START_REF] Crosetto | Réponses des consommateurs à trois systèmes d'étiquetage nutritionnel face avant[END_REF].

Evaluating the impact of an intervention is a key step that has to be rigorous, feasible and controlled [START_REF] Cambon | Transferability of interventions in health education: a review[END_REF][START_REF] Inserm | Inégalités sociales de santé en lien avec l'alimentation et l'activité physique[END_REF]. However, when nutrition prevention interventions are evaluated, the methodology generally used exhibits limitations due to declarative and social desirability bias Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 [START_REF] Maillot | Are the lowest-cost healthful food plans culturally and socially acceptable?[END_REF], 1-10. , DOI : 10.3945/cdn.117.001107 5 [START_REF] Fisher | Social Desirability Bias and the Validity of Indirect Questioning[END_REF][START_REF] Hebert | Social Desirability Bias in Dietary Self-Report May Compromise the Validity of Dietary Intake Measures[END_REF][START_REF] Norwood | Social Desirability Bias in Real, Hypothetical, and Inferred Valuation Experiments[END_REF]. To reduce such bias, the present study implemented a framed field experiment [START_REF] Harrison | Field Experiments[END_REF] to evaluate the impact of the intervention on food purchasing behavior.

The Opticourses project is multi-factorial, territorial and participative. It was implemented in disadvantaged neighborhoods in Marseille (France) with the aim of improving the nutritional quality of food purchases in populations with budgetary constraints [START_REF] Darmon | Opticourses [Internet[END_REF][START_REF] Marty | Higher nutritional quality at no additional cost among low-income households : insights from food purchases of "positive deviants[END_REF]. The project addressed both the supply side, through an in-store intervention [START_REF] Gamburzew | In-store marketing of inexpensive foods with good nutritional quality in disadvantaged neighborhoods: increased awareness, understanding, and purchasing[END_REF], and the demand side, through a prevention program based on participatory workshops. By focusing on household food supply, a daily activity that everyone knows and feels able to handle, the Opticourses program is engaging and pragmatic, in accordance with the principles of health promotion (28). The objective of the current study was to describe the co-construction of the Opticourses program with participants in deprived social situations and the evaluation of its impact on the nutritional quality and cost of household food purchases, using experimental economics.

Methods

Population characteristics

Recruitment of socio-economically disadvantaged individuals was carried out in community centers (n=9) and health & care centers (n=2) whose staff showed interest in the intervention and motivation to be involved. All were located in socio-economically deprived districts of Marseille, France. The participants volunteered to take part in an intervention that included a set of five two-hour workshops on "Diet and Budget". Inclusion criteria were: voluntary consent to participate in the study, residence in a socio-economically deprived district of Marseille (13th, 14th or 15th district), involvement in household food purchases, and financial difficulties as assessed by social workers. All the participants gave their written informed consent to participate in the study. No institutional review board approval was required for this research, as stated by the Comité de Protection des Personnes Sud-Méditerranée, which

Co-construction of protocol and tools

To maximize its effectiveness, the intervention was designed on the basis of the principles of co-construction and participative research. Participants were involved in the elaboration of the intervention, in order to implement a non-binding, playful intervention tailored to the target population. This co-construction approach integrates the principles of health promotion (28) and social cognitive theory [START_REF] Bandura | Health Promotion by Social Cognitive Means[END_REF]. It was applied to develop the protocol, and the tools of the intervention and evaluation process. The intervention tools were developed through an iterative process (Figure 1 Different versions of the intervention protocol were also tested in the co-construction stage.

The standardized tools and protocol were then used in the intervention stage.

Intervention

The Opticourses workshops aimed at guiding the participants toward household food purchases of good nutritional quality at no additional cost, building on better knowledge of food groups and nutritional quality of foods, awareness of foods combining good nutritional quality with a "fair price", knowledge and know-how sharing among participants (discussions on "tips and tricks", beliefs about food, recipes, etc.), collection of all the household food supply over a month [START_REF] Marty | Higher nutritional quality at no additional cost among low-income households : insights from food purchases of "positive deviants[END_REF], and advice based on the analysis of actual participants' food purchase practices.

7

The standardized protocol resulting from the co-construction stage took the form of five twohour workshops held every two weeks, except for the last workshop, mainly dedicated to evaluation, held one month after the fourth workshop. Workshops were group sessions (6-12 participants) organized in the community or health & care centers, and led by a professional in health promotion and nutrition and dietetics. An assistant took charge of data collection and helped in conducting the workshops. The workshops were built on real food purchases, including participants' household purchase receipts they collected over a month. Complete information on the Opticourses program content was provided during the first workshop, so that individuals not interested could decide to not attend the subsequent workshops. The main activities set during workshops were: discussions about food purchase strategies; information on the characteristics of food groups using a food group categorization game; information on the nutritional quality of foods using a game where food was classified into four nutritional quality classes based on the SAIN,LIM nutrient profile system [START_REF] Darmon | Nutrient profiles discriminate between foods according to their contribution to nutritionally adequate diets: a validation study using linear programming and the SAIN,LIM system[END_REF]; overview of the notion of nutritional quality for price (NQP) based on a list of foods with both good nutritional quality and a low price within each food group, and the "fair price booklet" tool (31) (tool providing a list of foods with good nutritional quality and the price below which the product could be considered as relatively inexpensive); analysis of real food purchases by the participants using a game consisting in classifying food expenditure by food groups; working on beliefs about food using a tasting game (participants blindly compared the taste of commonly consumed foods of equivalent nutritional quality but of different prices and brands). During the fourth workshop, after an analysis of monthly household food receipts, the research team gave individual feedback to participants on the nutritional quality of their food purchases and the contribution of each food group to total food expenditure, and offered advice on how to improve the nutritional quality of their food purchases at no additional cost.

Quantitative evaluation

Evaluating the impact of the intervention on knowledge

Two tools were developed to evaluate the impact of the intervention on knowledge: the "food group test" and "NQP test". Both tests were taken voluntarily by the participants, before and after the intervention. In the "food group test", the participants were asked to assign a color code (e.g., green for fruit and vegetables, blue for dairy products, etc.) to 14 foods pictures. In the "NQP test", 10 pairs of foods were presented to the participants, each pair made up of foods differing in their NQP. Each pair was composed either of similar foods with a similar price but different nutritional content (e.g. whole-grain sliced bread at 1.75€ per kg vs. white sliced bread at 1.73€ per kg), or foods belonging to the same food group, with similar prices and different nutritional quality (e.g. canned chickpeas at 1.62€ per kg vs. frozen fried potatoes at 1.64€ per kg), or foods with similar nutritional quality but different prices (e.g., two types of potato flakes at 3.90 € per kg (National brand) or 1.78 € per kg (Discount version)), or two different foods (i.e., of different nutritional quality) but consumed similarly during meals (e.g. sweet flan at 2.60€ per kg vs. fruit compote at 2.75€ per kg). Participants were instructed to pick the food in each pair they would advise a friend to buy when he/she wants to balance his/her food purchases with a limited budget. For both tests, a global score was computed as the total points obtained from correct answers (wrong or non-responses were ignored).

Evaluating the impact of the intervention on food purchasing behavior using experimental economics

A catalogue of 300 food items (http://www.opticourses.fr/node/24) was specifically developed for the study, based on prices and pictures of foods collected a few months before the intervention from a supermarket located in the participants' neighborhood. Each page displayed pictures of food front packages, unit prices (€) and prices per kilo, as done in supermarket advertising catalogues. Use of the same catalogue ensured that participants were 1). The participants' task consisted in selecting foods for the next two days for their household, based on food items featured in the catalogue. This selection constituted a food purchase intent. Just as when doing their regular shopping, participants were free to choose the nature and amount of food they wanted to select. To avoid potential bias related to the declarative nature of these purchase intents, the task was made incentive-compatible, by informing participants that they could earn a 10€ coupon if their next food purchases in a real store reflected their purchase intent during the experiment. They were thus prompted to shop in the experiment as they would in a real food store. At the following workshop, shopping receipts of real food purchases brought by participants were confronted with their experimental food purchases. To get the coupon, the shopping receipts had to feature at least six items corresponding to the experimental purchase intents. The objective of this incentive was to assess true changes in food purchase behaviors by limiting the effects of social desirability, i.e. when participants direct their choices to please or impress the workshop facilitator. Workshop participants (intervention group) took part in two experimental sessions (at the first and last workshops), and the changes in their experimental purchases were compared between baseline and endline. In addition, to assess if having already performed the test affects the experimental purchases of the subsequent session, a control group composed of 23 persons recruited in the same community centers, but who did not participate in the workshops, also took part in two experimental sessions of food purchase intents at three-week intervals (baseline and endline), based on the same instructions and protocol than workshop participants i.e. using the catalogue and incentive with coupon.

Our hypothesis was that workshops could help improving the balance of food purchases, and consequently their nutrient content, with no additional cost. Thus, the nutritional Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 [START_REF] Maillot | Are the lowest-cost healthful food plans culturally and socially acceptable?[END_REF], 1-10. , DOI : 10.3945/cdn.117.001107 10 characteristics of the experimental purchases were assessed both at the food group and nutrient levels. For that purpose, each food in the catalogue was associated with a nutritional composition for 100g of food as consumed, based on the French CIQUAL database (Centre d'Information sur la Qualité des Aliments, https://pro.anses.fr/tableciqual/index.htm) that states the nutritional composition and edible portion of French food products. Total weight (grams per day per person) and total energy content (kcal per day per person) were estimated for each experimental purchase by summing the weight (as consumed) and energy content of all the foods and drinks selected, and dividing it by the number of household members and days for which purchases were planned. In addition to the classification into 22 categories relevant to the retail environment, as mentioned previously, all foods in the catalogue were classified into 8 groups (Starch, Fruit and Vegetables, Meat-Fish-Eggs, Dairy products, Fats, Foods high in fat/salt/sugar (HFSS), Mixed dishes, and Juices and soft drinks) derived from the French National Nutrition and Health Program [START_REF] Hercberg | The French National Nutrition and Health Program: 2001-2006-2010[END_REF]. Contribution of these 8 food groups to total food purchases was estimated in weight and energy. Water was excluded from all the analyses since it was mainly tap water.

The Mean Adequacy Ratio (MAR) and the Solid Energy Density (SED) were used to assess the nutritional quality of the experimental food purchases, as previously described by Vieux et al. [START_REF] Vieux | High nutritional quality is not associated with low greenhouse gas emissions in self-selected diets of French adults[END_REF]. In addition, three nutrients to be limited were also assessed, namely sodium, saturated fatty acids (SFAs) and free sugars. The nutritional quality assessment methodology is fully described in Supplemental File.

Based on experimental food purchases selected by the participants and food prices from the catalogue, the total expenditure (€/pers*d) and energy cost (€ per 2000kcal) were estimated for each experimental food purchase. 11 How the participants perceived the impact of the workshops on their food purchases was assessed by a qualitative evaluation. Individual semi-directed interviews and one group interview were conducted by an external evaluator one month after the intervention, using an interview grid including questions about modification of food purchases. These interviews were proposed to participants coming from the different community or health centers, yielding a sub-sample of 19 interviews. Interviews were recorded using field notes and transcribed. Interview transcriptions were analyzed using conventional content analysis [START_REF] Hsieh | Three Approaches to Qualitative Content Analysis[END_REF] and categorized thematically.

Qualitative evaluation

Statistical analysis

Descriptive and statistical analyses were performed using the SAS 9.4 software. Sociodemographic characteristics were compared (a) between workshop participants who performed the experimental economics quantitative evaluation (evaluated intervention group) vs. those who did not (non-evaluated intervention group), and (b) between intervention vs. control groups using the non-parametric chi-squared test for qualitative variables and the Mann-Whitney test for continuous variables. Within the evaluated intervention group, the scores of the 'Food group' and 'NQP' tests, and the nutritional characteristics and food composition of the experimental purchases were compared between baseline and endline (i.e. before vs. after the intervention) using a paired t-test and a generalized linear mixed model for repeated measures (with a compound symmetry covariance matrix) for adjustment on age, gender, the financial situation, number of individuals in the household and number of children. Within the control group, the nutritional characteristics and food composition of experimental food purchases were compared between the first and second session of experimental food purchases (i.e., baseline vs. endline) using paired t-tests as well with a generalized linear mixed model for repeated measures for adjustment on age, gender, the financial situation, number of individuals. Effect sizes for dependent groups (Cohen'

Results

Characteristics of the population

In all, 96 persons ( 9 (Supplemental Figure 1). Socio-demographic characteristics were not significantly different between the workshop participants who completed the evaluation and those who did not (Table 1). Evaluated workshop participants were mainly women (77%), with a mean age of 51y and a mean number of household members of 3.1, including 1.3 children; 44% declared severe financial difficulties (Table 1). Socio-demographic characteristics were not significantly different between evaluated workshops participants and the control group, except for age, which was significantly lower in the control group (45.4y vs. 50.9y, p=0.038) (Table 1). Participation rates in the five workshops varied (Figure 2): 94% of intervention participants attended the first workshop, and the participation rate then remained relatively stable (40-48%) over the following four workshops.

Impact on knowledge

Scores obtained in the "food group test" were significantly higher after the participative workshops than those obtained before the intervention (13.2 ± 1.8 and 12.1 ± 1.9 respectively, p<0.01). Scores of the "NQP test" were not significantly different before and after the intervention (6.6 ± 1.4 and 6.9 ± 1.6, respectively, p=0.30).

Impact on food purchasing behavior: experimental economics evaluation

Table 2 shows the nutritional characteristics and cost of experimental food purchases of workshops participants before and after the intervention. The energy content of the experimental food purchases significantly decreased by 38% after the participative workshops (5114 vs. 3385 kcal per person per day, p<0.01 for both crude and adjusted p-values), as did the food expenditure (9.73 vs 7.22 € per person per day, p<0.01 for both crude and adjusted pvalues). However, energy cost remained unchanged. The SED decreased from 128 kcal/100g to 119 kcal/100g after the intervention (crude p<0.04), i.e. a reduction of 7.6%, but the significance was lost after adjustment. The MAR did not change significantly. The energy contribution of free sugars decreased significantly from 8.5% to 5.8% (p<0.01 for both crude and adjusted p-values), while that of SFA and sodium content expressed for 2000kcal remained similar. The contribution of food groups to the total energy of the experimental purchases was significantly different at baseline and endline (Table 2). Percent energy from the HFSS group was halved (from 11.0 to 5.5%, p<0.01 for both crude and adjusted p-values).

In parallel, a decrease occurred in the energy contribution from fruit and vegetables (from 10.1 to 13.6% of total energy, crude p=0.03) and from meat-fish-eggs (from 15.8 to 21.1% of total energy, crude p=0.02,), but the statistical significances of those changes were lost after adjustment (adjusted p=0.06 for both food groups). Based on the classification proposed by Cohen (36), the calculated effect sizes (d) were medium for energy content (d=0.5) and the energy contributions from proteins (d=0.6), free sugars (d=0.5), meat-fish-eggs (d=0.5) and HFSS (d=0.5). Effect sizes were small for the food expenditure (d=0.4), the SED (d=0.3) and the energy contribution from fruits and vegetables (d=0.4) (Table 2).

In the control group, none of the characteristics of experimental food purchases were significantly different between the two sessions (all p>0.05, Table 3). In particular, the mean

Qualitative evaluation

The analysis of participants' declarations highlighted their improved knowledge about the nutritional quality of foods (e.g., the difference in nutritional quality between potatoes and vegetables, and between sweet dairy desserts and yogurts), and their awareness of the share of their food budget allocated to the different food groups. Fifteen out of the 19 participants interviewed 1 month after the intervention gave concrete examples indicating how they had modified their food purchase behavior. The analysis of participants' declarations identified three types of modification: changes in the type of foods purchased, changes in purchasing attitudes and strategies, and changes in culinary practices. Among changes in the type of foods purchased, soft drinks were the most frequently cited. One person in three declared they had reduced or even stopped their purchases of sodas and/or replaced their purchases of fruit 'nectars' (i.e. sugared fruit juices) by fruit juices. Other modifications of foods purchased were expressed in terms of quantity (e.g. increased legumes or fruits and vegetables purchases) and quality (e.g. substitution of white bread by whole-grain bread). The changes in purchasing attitudes and strategies included more attention paid to labeled information (product composition and price per kilo), changes and/or diversification of purchasing points, improved opinion of cheaper brand products, retrieval and purchases of these products, and better control of food budget. The changes in culinary practices included cooking oneself, or cooking differently (e.g., less fat, more vegetables). The following synthesis of transcripts illustrates the different modifications to food purchase behaviors: "Now, after shopping for food, I still keep the receipts. They help me check if I've managed my budget well. I look at the price per kilo of foods and don't get confused with orange juices anymore (sugar and fruit). I've bought canned fish, and several times I've prepared some "I buy cheaper brand products, before I never did because I thought they were poorer quality.

I know how to tell the real juices from the ones with only sugar: I buy the real ones and I don't buy sodas anymore. I buy whole-grain bread instead of white bread. For minced meat, I look and I take no more than 12% fat, 5% I can't, it's too expensive. I've changed many things, I spend 330€ (per month) instead of 360€ before, so it's a bit cheaper and I'm purchasing better things. I use more different oils, I like canola oil, I blend them. I also try to add less salt. I used to buy a lot of sweet products. I buy a bit more fish, beef and chicken and less pork. I diversify shops a bit (Aldi, Leader Price) but I don't have a car, it's not easy." (Female,51y) Participants were able to analyze their own food purchases and identify ways to improve them, as supported by several transcripts: "I realized the burden of sweet products in my food budget" (group interview); "For me it's easy since I save money and it's a true motivation" (Female, 59y); "Now I look at what I purchase, I used not to necessarily" (group interview); "I look differently when I do my shopping" (Female, 42y); "I look at labels more carefully, especially the price per kilo."(Female, 53y). The present study shows that co-constructed participative workshops based on recreationalentertaining activities around food purchase practices and nutritional quality and price of foods can favorably change food purchasing behaviors of individuals in deprived social situations without significantly increasing their food expenditure. Interviews revealed three types of change in purchasing behaviors: changes in the type of foods purchased, changes in purchasing attitudes and strategies (attention paid to label information, purchasing points, and opinion on cheaper brand products), and changes in culinary practices. Quantitative evaluation of the intervention was performed on food purchase intents using experimental economics to limit social desirability bias. Unlike controls, workshop participants decreased the total energy of their experimental food purchases (toward more realistic energy levels), suggesting a better ability to assess the needs of their households for 2 days and adapt purchases accordingly. The evaluation also showed that the intervention improved food purchasing behaviors, as indicated by decreased energy contribution from free sugars and from products high in fat, salt, and sugar, and nearly significant increased energy contribution from fruit and vegetables (adjusted p-value=0.06) at the endline in the intervention group only, and at no additional cost.

Discussion

Similar reduction in the total number of calories purchased were previously observed in lowincome families in the US who received home-based nutrition education sessions [START_REF] Cortés | Food Purchasing Selection Among Low-Income, Spanish-Speaking Latinos[END_REF] 17 than on food intake can induce a stronger motivation of the participants, which is a success factor for interventions in health education [START_REF] Peters | Outil de pilotage et d'analyse de l'efficacité attendue des interventions en promotion de la santé. Preffi 2.0. Guide explicatifs, les fondements de Preffi[END_REF].

Many population-directed policies designed to improve the nutritional quality of food purchase rely on enhancing access to information [START_REF] Downs | Strategies for Promoting Healthier Food Choices[END_REF]. The underlying assumption is that people act rationally when making food choices. In economics jargon, rationality means that consumers maximize their lifetime happiness when they allocate their scarce resources of time and money [START_REF] Cawley | An economic framework for understanding physical activity and eating behaviors[END_REF]. Nonetheless, various studies have shown that the provision of nutritional information has moderate effects [START_REF] Downs | Strategies for Promoting Healthier Food Choices[END_REF][START_REF] Bassett | Purchasing Behavior and Calorie Information at Fast-Food Chains in New York City, 2007[END_REF][START_REF] Burton | Attacking the Obesity Epidemic: The Potential Health Benefits of Providing Nutrition Information in Restaurants[END_REF][START_REF] Finkelstein | Mandatory Menu Labeling in One Fast-Food Chain in King County, Washington[END_REF][START_REF] Harnack | Effects of calorie labeling and value size pricing on fast food meal choices: Results from an experimental trial[END_REF]. The main reason may be that consumers do not behave as Econ [START_REF] Kahneman | Maps of Bounded Rationality: Psychology for Behavioral Economics[END_REF]. For instance, consumers have a limited capacity to process information and may even be distracted when provided with additional information [START_REF] Simon | A Behavioral Model of Rational Choice[END_REF]. In that respect, the Opticourses workshops focused on tacit knowledge (know-how) rather than explicit knowledge (know-what). With tips & tricks on food purchasing (fair price booklet, real purchase analyses), the intervention provided participants with practical knowledge on how to build healthy diets. By doing so, the Opticourses workshops provide participants with the necessary tools for fast and frugal food decision making, allowing the construction of healthier diets despite bounded rationality [START_REF] Gigerenzer | Fast and Frugal Heuristics: the Tools of Bounded Rationality[END_REF].

Different reports and studies explored the levers for effective interventions on diet, in particular for socioeconomically disadvantaged populations [START_REF] Peters | Outil de pilotage et d'analyse de l'efficacité attendue des interventions en promotion de la santé. Preffi 2.0. Guide explicatifs, les fondements de Preffi[END_REF][START_REF] Who | Interventions on diet and physical activity[END_REF][START_REF] Inserm | Inégalités sociales de santé en lien avec l'alimentation et l'activité physique[END_REF][START_REF] Mcgill | Are interventions to promote healthy eating equally effective for all? Systematic review of socioeconomic inequalities in impact[END_REF][START_REF] Oldroyd | The effectiveness of nutrition interventions on dietary outcomes by relative social disadvantage: a systematic review[END_REF][START_REF] Reicks | Impact of cooking and home food preparation interventions among adults: outcomes and implications for future programs[END_REF][START_REF] Brandstetter | A systematic review on empowerment for healthy nutrition in health promotion[END_REF][START_REF] Ball | Traversing myths and mountains: addressing socioeconomic inequities in the promotion of nutrition and physical activity behaviours[END_REF]. A WHO report assessing the evidence on effective interventions on diet and physical activity [START_REF] Who | Interventions on diet and physical activity[END_REF] underlined that multi-component interventions adapted to the local context and involving participants in the planning and implementation stages were found to be the most successful.

Co-construction was a key component of the present study to engage participants, with a specific attention given to the format of the intervention to be both playful, with multiple, diversified activities, and with reachable goals. Empowerment is known to be a success factor in health promotion in the field of nutrition [START_REF] Brandstetter | A systematic review on empowerment for healthy nutrition in health promotion[END_REF]. This is particularly true for vulnerable [START_REF] Inserm | Inégalités sociales de santé en lien avec l'alimentation et l'activité physique[END_REF]. The present workshops enabled participants to appropriate tools and knowledge to act favorably on their purchases, thus enhancing auto-efficacy and self-esteem. Moreover, conducting the intervention in the form of group workshops has been identified as a key lever to improve the effectiveness of interventions promoting nutrition and physical activity among socioeconomically disadvantaged populations [START_REF] Ball | Traversing myths and mountains: addressing socioeconomic inequities in the promotion of nutrition and physical activity behaviours[END_REF].

Interventions promoting healthy eating are generally evaluated through self-reported and so potentially biased dietary intakes or behaviors [START_REF] Reicks | Impact of cooking and home food preparation interventions among adults: outcomes and implications for future programs[END_REF][START_REF] Perez-Escamilla | Impact of Peer Nutrition Education on Dietary Behaviors and Health Outcomes among Latinos: A Systematic Literature Review[END_REF]. The experimental economics approach has already been used in public health and nutrition to assess food tax [START_REF] Darmon | Food price policies improve diet quality while increasing socioeconomic inequalities in nutrition[END_REF] and labeling policies [START_REF] Muller | Modification des achats en réponse à l'apposition de différents logos d'évaluation nutritionnelle sur la face avant des emballages[END_REF]. To our knowledge, the present study is the first to implement this approach in an innovative way to evaluate the impact of a nutritional intervention in a real setting.

Experimental economics limits social desirability bias, and so reveals true consumer preferences by using incentive mechanisms [START_REF] Harrison | Experimental Evidence on the Existence of Hypothetical Bias in Value Elicitation Methods (Chapter 81)[END_REF]. Also, placing participants under controlled conditions, as close as possible to those of the real world, ensured that the observed changes in purchasing behavior were not influenced by modifications in the purchasing environment (diversity and price of food supply, purchasing points, etc.). In addition, the conditions of implementation of the evaluation method were tailored for a target population with potentially low literacy skills. While questionnaires could be perceived as demanding, normative and difficult to fill out, the food catalogue and instructions given placed the participants in a comfortable day-to-day activity that preserved their self-esteem. The main strength of this study is that it improved food purchasing behaviors despite the limited room for maneuver in terms of economical means. Participants had a low budget for food (previously estimated at The present study has limitations. In the intervention stage, attrition rate was approximately 50% after the first workshop. This was expected, because recruitment is known to be difficult in low-income populations [START_REF] Inserm | Inégalités sociales de santé en lien avec l'alimentation et l'activité physique[END_REF][START_REF] Smith | Minority recruitment and participation in health research[END_REF]. The high attrition rate may reflect a sensible economic decision about the time/benefit ratio of attending the workshops [START_REF] Cawley | An economic framework for understanding physical activity and eating behaviors[END_REF]. However, the participation rate in the following workshops, once the participants had understood and agreed with the format and contents of the intervention, remained stable, which highlights the importance of providing complete information and engaging people during the first workshop.

Another limitation is that the quantitative evaluation was only performed by a sub-sample of intervention participants, was not randomized, and did not assess the long-term effect of the intervention. However, the participants who carried out the quantitative evaluation (n=35)

were not significantly different in terms of socio-demographic characteristics from those who did not (n=58), the specificity of the observed changes were tested with a control group (n=23), and the sample sizes were sufficient to highlight significant differences between the control and intervention groups. In addition, the endline experimental food purchases of the control group were assessed after a shorter interval of time (3 weeks) than the intervention group (10 weeks). This may have introduced a bias in the design but allowed to limit the attrition rate that might have been higher in control after 10 weeks. Also, the evaluation tools were new and not quantitatively validated, but face validity was assessed by researchers and participants who evaluated whether the items were relevant to assess the measured concept, and acceptability and feasibility were tested with the co-construction group. Finally, the size of the effects was medium or small. However, moderate effects were expected since it is unlikely that an intervention on its own induces radical shifts in food purchase behaviors. These moderate effects can comfort the idea that social desirability bias was limited and that participants revealed true choices.

The present study shows that co-constructed participative workshops, based on actual food purchase practices, can guide individuals in deprived social situations towards household food purchases of better nutritional quality without increasing their food expenditure. It shows relevance and feasibility of using experimental economics for evaluating the impact on food purchasing behavior of a public health nutrition intervention conducted in a real setting. The "game-like" aspect of the experimental economics approach enables participants to deliver unbiased evaluations, while preserving their self-esteem.

33

where Q bn is the quantity of each beneficial nutrient (bn) adjusted to a total energy of 2000 kcal, and RDA bn is the corresponding Recommended Dietary Allowance (RDA) for this nutrient. The age and gender being known for the study participants but not for each member of their households, the average value of the RDA for adult men and women has been used.

The reference values for the 23 recommended nutrients are given in Supplemental Table 2.

The contribution from each nutrient was capped at 100% so that a high intake of one nutrient could not compensate for the low intake of another [START_REF] Darmon | Does social class predict diet quality?[END_REF]. The SED, calculated as the ratio between total energy and total weight and expressed in kcal/100g was also used as an indicator of nutritional quality. As proposed by Ledikwe et al. [START_REF] Drewnowski | The economics of obesity: dietary energy density and energy cost[END_REF], only items typically consumed as foods, including soups, were included in the calculation of SED, whereas foods typically consumed as beverages, such as milk, juices, and other drinks, were excluded. Three nutrients to be limited were also assessed, namely sodium (expressed in mg/d*pers and mg/2000kcal), saturated fatty acids (SFAs) and free sugars, both expressed in percentage of total energy. The term "free sugars" refers to added sugars plus sugars naturally present in honey, syrups, and fruit juices (3). The free sugar content of each food item had previously been added to the CIQUAL database (4).

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 6 reviewed the protocol of the Opticourses intervention. This trial was registered at clinicaltrials.gov as NCT02383875.

  ): initial proposition of a tool by the research team, based on operational objectives, participants' expectations expressed in early workshops, estimated feasibility and cost; design of a first version by the research team; testing of the first version by the participants during the workshops and collection of information, both qualitative (understanding, participants' opinion, time of use) and quantitative (test answers, consistency of results); development of improved versions that were re-tested; validation and finalization.

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

  groups, 8 centers) participated in the co-construction stage (September 2012-April 2013). Then, 93 persons (14 groups, 7 centers) took part in the intervention stage, with intervention in site 1 starting in April 2013 and intervention in site 7 ending in June 2014. Thirty-five persons took part in the evaluation of knowledge and in the food purchase experiment, i.e. 38% of the intervention participants; 23 other persons (3 sites) also took part in the food purchase experiments, but without participating in the workshops (control group)

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 14 energy contents were 4523 and 4711 kcal/pers*d at baseline and endline respectively (p=0.71).

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 lovely dishes with raw vegetables and sardines. When I'm cooking starches, I add some fresh vegetables. I shared the tips and tricks with my friends who by the way have noticed that I've changed the way I cook." (Female, 51y) "I buy too much fat, I've cut back a bit. I buy more fruit and vegetables, it doesn't get too expensive for me, I do my shopping at Noailles [very popular market in the center of the town]. I already used to, but I wasn't buying much fruit and legumes. I also buy more legumes (red beans and lentils). I used to shop at Dia or Simply markets and now I go to Carrefour, the other participants told me it's less expensive and it's true. I pay more attention to labels and especially the price per kilo" (Female, 46y).

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 16

  To our knowledge, most individual-directed interventions to promote healthy eating are based on activities around food consumption or cooking skills (38-40). Yet, changing food consumption behavior implies changing food purchasing behavior. An originality and asset of the present study was to use food purchases and prices as an entry point to address the question of healthy diet with individuals in deprived social situations. Implementing workshops on food purchases a major daily, tangible concern for this population -rather Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 18 populations, who are more prone to low self-esteem

3 .

 3 65€/pers*d (26)), very close to the lowest cost at which a nutritionally adequate diet can be achieved (~3.5€/pers*d) as estimated by Darmon et al. (9), and very close to the cost of 2000kcal of experimental food purchases in the present study. The beneficial changes in food Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.00110719 purchasing behaviors could be explained by the anticipation and rationalization of food purchasing highlighted by the decrease in the total energy of experimental food purchases after the intervention. Workshop participants may have realized the importance of the act of purchase, and of purchasing foods rationally rather than automatically/routinely.

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 20

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

Figure legends Figure 1 .Figure 2 .

 legends12 Figure legends

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

35 Supplemental Figure 1 :

 351 : 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 Flow chart of the study Supplemental References 1. Vieux F, Soler L-G, Touazi D, Darmon N. High nutritional quality is not associated with low greenhouse gas emissions in self-selected diets of French adults. Am J Clin Nutr. 2013;97:569-83. 2. Ledikwe JH, Blanck HM, Khan LK, Serdula MK, Seymour JD, Tohill BC, Rolls BJ. Dietary energy density determined by eight calculation methods in a nationally representative United States population. J Nutr. 2005;135:273-8. 3. World Health Organization. Diet, Nutrition, and the Prevention of Chronic Diseases: Report of a Joint WHO/FAO Expert Consultation. WHO technical report series 916. Geneva, Switzerland: WHO; 2003. 4. Bocquier A, Vieux F, Lioret S, Dubuisson C, Caillavet F, Darmon N. Socio-economic characteristics, living conditions and diet quality are associated with food insecurity in France. Public Health Nutr. Cambridge University Press; 2015;1-10.

5 .

 5 Martin A. Apports nutritionnels conseillés pour la population française. 3ème édition [Recommended nutritional intakes for the French population]. AFSSA. Paris, France: Lavoisier; 2001. 660 p. in the study Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

Figure 1 . 1 Figure 2 .

 112 Figure 1.

20%

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Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

Table

	Downloaded from	cdn.nutrition.org	on October 17, 2017 -First published online on September 13, 2017 in Current Developments in
			Nutrition. DOI: 10.3945/cdn.117.001107
			9
	faced with the same supply and diversity of foods throughout the study. Foods were grouped
	in the catalogue according to a retail-based categorization (22 categories, Supplemental
		Comment citer ce document :
	Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon,
	N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional
	quality of food purchases at no additional cost in a socio-economically disadvantaged
	population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from

  s d (35))

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			Nutrition. DOI: 10.3945/cdn.117.001107
			12
	were computed for significant variables. The significance level was set at 5% (p < 0.05) for
	all the tests.

Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from

Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

[START_REF] Darmon | Low-cost foods: how do they compare with their brand name equivalents? A French study[END_REF]

Table 1 .

 1 Population characteristics Results are mean ± SD or %,1 from Chi-squared test of homogeneity for qualitative variables and Mann and Whitney test for continuous variables to test difference between participants who did vs. did not complete the evaluation; 2 from Chi-squared test of homogeneity for qualitative variables and Mann and Whitney test for continuous variables to test difference between evaluated intervention participants vs. controls. Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1[START_REF] Maillot | Are the lowest-cost healthful food plans culturally and socially acceptable?[END_REF], 1-10. , DOI : 10.3945/cdn.117.001107[START_REF] Bandura | Health Promotion by Social Cognitive Means[END_REF]

	Tables							Downloaded from
	Age, y (n) Number in household (n) Number of children (n) Women, % (n) Financial situation, % (n) Stable Precarious Severe difficulties	Co-construction (n=96) 48.4 ± 7.7 (67) 3.7 ± 2.0 (62) 2.0 ± 1.7 (59) 80.0 (96) (48) 12.5 52.1 35.4	Intervention (n=93) Non-evaluated (n=58) 50.9 ± 11.2 (34) 47.0 ± 13.0 (27) Evaluated (n=35) 3.1 ± 1.8 (35) 2.3 ± 1.4 (25) 1.3 ± 1.5 (35) 1.2 ± 1.4 (22) 77.1 (35) 70.7 (58) (34) (17) 11.8 17.7 44.1 47.1 44.1 35.3	p-value 1 0.094 0.080 0.941 0.496 0.770	Control ± (23) 3.3 ± 1.6 (23) 45.4 9.6 1.6 ± 1.3 (23) 91.3 (23) (23) 13.0 47.8 39.1 (n=23)	p-value 2 0.038 0.186 0.135 0.163 0.932	Nutrition. DOI: 10.3945/cdn.117.001107	on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org

Table 2 .

 2 Nutritional and cost characteristics of experimental food purchases of workshops participants (n=35) before the intervention (baseline) and after it (endline).

	Baseline	Endline	p-value 1 Adjusted p-value 2	Effect size 3

, Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107 30

Table 3 .

 3 Nutritional and cost characteristics of experimental food purchases of the control group (n=23) during the first session (baseline) and the second session (endline)

	Baseline	Endline	p-value 1 Adjusted p-value 2

Comment citer ce document : Perignon, M., Dubois, C., Gazan, R., Maillot, M., Muller, L., Ruffieux, B., Gaigi, H., Darmon, N. (2017). Co-construction and evaluation of a prevention program for improving the nutritional quality of food purchases at no additional cost in a socio-economically disadvantaged population. Current Developments in Nutrition, 1 (10), 1-10. , DOI : 10.3945/cdn.117.001107

34 Supplemental Table 2 .

 Supplemental2 Reference values for the 23 recommended nutrients used in the 647 calculation of the Mean Adequacy Ratio 648

	Nutrient	Reference value 1
	Proteins (g/d)	60
	DHA (mg/d)	0.11
	Fiber (g/d)	30
	Linolenic acid (g/d)	1.8
	Linoleic acid (g/d)	9
	Vitamin A (mcg/d)	700
	Vitamin B6 (mg/d)	1.7
	Vitamin D (mcg/d)	5
	Thiamin (mg/d)	1.2
	Riboflavin (mg/d)	1.6
	Niacin (mg/d)	13
	Folates (mcg/d)	315
	Vitamin B12 (mcg/d)	2.4
	Vitamin C (mg/d)	110
	Vitamin E (mg/d)	12
	Calcium (mg/d)	900
	Potassium, (mg/d)	3100
	Magnesium, (mg/d)	390
	Iodine (mg/d)	150
	Selenium (mcg/d)	55
	Copper (mg/d)	1.8
	Zinc (mg/d)	11
	Iron (mg/d)	13
	1 Mean of the recommended dietary allowances for
	men and women (5)

  Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from

		100%
		90%
		80%
	P a r t i c i p a t i o n r a t e	50% 60% 70%
		40%
		30%
		Workshop 1	Workshop 2	Workshop 3	Workshop 4	Workshop 5

Nutrition. DOI: 10.3945/cdn.117.001107 on October 17, 2017 -First published online on September 13, 2017 in Current Developments in cdn.nutrition.org Downloaded from

Acknowledgments

We thank the scientists, dieticians, project manager and assistants who helped carry through the Opticourses project, and all the study participants.

This work was funded by the Regional Health Agency in the Provence Alpes Côte d'Azur Region (ARS PACA) and the French National Cancer Institute (INCA).

The funding bodies had no role in the protocol design, analysis or interpretation of the data, writing the manuscript, or the decision to submit the manuscript for publication.

Conflict of interest:

The authors declare that they have no conflict of interest.

Authors' contributions: ND, CD and HG designed and conducted the intervention. MP, CD and ND interpreted the data and drafted the manuscript. MM and RG analyzed the data. LM and BR designed the experimental economic assessment and were involved in the interpretation of the results. All authors critically reviewed the manuscript and approved the final version.

Online Supporting Material

Supplemental method: Nutritional quality of food purchases

The MAR was used as an indicator of nutritional quality, as previously described by Vieux et al. [START_REF] Darmon | Does social class predict diet quality?[END_REF], to evaluate if the workshops helped improve the nutritional content of food purchases for a whole set of nutrients. The MAR, expressed for 2000 kcal, was calculated as the mean percentage of daily recommended intakes for [START_REF] Norwood | Social Desirability Bias in Real, Hypothetical, and Inferred Valuation Experiments[END_REF]