Changes in the healthfulness of food and beverage purchases from 2006 to 2022 in formal, mixed, and informal outlets in Mexico

doi:10.21203/rs.3.rs-5291350/v1

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Research Article

Changes in the healthfulness of food and beverage purchases from 2006 to 2022 in formal, mixed, and informal outlets in Mexico

https://doi.org/10.21203/rs.3.rs-5291350/v1

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Background

To better inform retail food environment policies in the global south, it is necessary to further understand the healthfulness of food and beverages purchased by type of food outlet over time.

Methods

Using repeated cross-sectional data from the National Income and Expenditure Survey (ENIGH) in Mexico (2006 to 2022), we categorized food outlets as formal (supermarkets, chain convenience stores), informal (street markets, street vendors, acquaintances), fiscally mixed (public markets, small neighborhood stores, specialty stores), and others. We estimated the proportion of total purchases in each food outlet and the percentage of the types of foods purchased by outlet for the overall sample and stratified by education level and urbanicity.

Results

In 2006, the food outlets with the largest proportions of ultra-processed foods purchases were chain convenience stores (49%), small neighborhood stores (37%) and supermarkets (35%). In contrast, the outlets with the highest proportions of minimally processed food purchases were street markets (83%), public markets (81%), and specialty stores (75%). Over time, households improved the proportion of expenditure in minimally processed foods in supermarkets and slightly in small neighborhood stores (49 to 54% and 46 to 47%, respectively). Conversely, the proportion of expenditures in minimally processed foods decreased from 70 to 62% in street vendors. Households without formal education and residing in rural localities increased their minimally processed food purchases in specialty stores, but decreased in street vendors, acquaintances and public markets. Households with higher education and residing in more urbanized areas increased their purchases of minimally processed foods in supermarkets and small neighborhood stores and decreased in street vendors. These households also increased in ultra-processed foods in chain convenience stores.

Conclusions

Over time, purchases from informal outlets were healthier compared to purchases from the formal and mixed sectors, but no outlet sold only healthy or unhealthy foods. To ensure access to healthy foods, food policies should consider where the largest proportion of food purchases is being made, where the healthiest and unhealthiest purchases are, and why some purchases from certain food outlets are becoming healthier, while in others they are becoming less healthy.

Food purchases

healthfulness

formal-informal

longitudinal

ENIGH

processing levels

urbanicity

education

Mexico

The food environment in the global south is more varied than in the global north [1,2]. Despite the increased penetration of formal outlets such as supermarkets and chain convenience stores in the global south, a wide variety of food retailers outside the formal sector prevail. Small neighborhood stores, specialty stores, and public markets still predominate [3,4], and the presence of the informal food sector is ubiquitous [1,2,5–8]. Recent studies have tried to better understand the retail food environment in Mexico and its relationship with health [9–14]; however, little is known about the quality of food purchases at different food retailers. Thus, studies that use the density of food outlets or those that seek to develop or use an aggregate measure of food environment healthfulness (e.g., similar to the Retail Food Environment Index) [15,16] might be limited because it is unclear whether prevalent retailer types (e.g., public markets, small neighborhood stores, specialty stores) and formal outlets (e.g., supermarkets, chain convenience stores) should be considered healthy, unhealthy, or a mix of both. Moreover, these studies do not consider the informal sector, despite informality accounting for more than 23.7% of Mexico’s Gross Domestic Product (GDP) [17].

Recent research has made initial efforts to better understand the contribution of the different food outlets to total food purchases in Mexico [18,19]. In 1994, household purchases from mixed outlets (i.e., those without a clear definition of formality) represented 73.4% of total food purchases, followed by formal (12.8%), informal (12.3%), and other outlets (1.5%). By 2020, mixed outlets represented 71.6% of total food purchases, followed by informal (13.7%), formal (13.4%), and other outlets (1.3%) [18,19]. Another study using cross-sectional data from 2018 quantified what proportion of the total foods purchased by Mexican households the proportion of total foods purchased by Mexican households that was purchased at different types of food outlets [20]. They found that most unhealthy foods were purchased at small neighborhood stores and supermarkets, while healthy foods were predominantly purchased at markets and specialty stores [20]. Yet, little is known about the changes in the healthfulness of food purchases in the different food outlets over time, despite secular increases over the last decades in prevalence of diet-related chronic diseases among the Mexican population, as well as increases in distribution and density of formal food outlets, particularly of supermarkets and chain-convenience stores.

Several high-profile initiatives have implemented policies targeting the food environment to improve diet quality and address global secular increases in diet-related chronic diseases (e.g., INFORMAS) [21,22]. However, the evidence regarding these policies is scant and largely focused on the global north [22]. It is unclear whether policies designed and tested in the global north will be contextually relevant for the global south. Thus, to better inform retail food environment policies to ensure access to healthy foods for the entire population, it is imperative to understand how different types of food retailers contribute to food purchases. To address these gaps, we used the National Income and Expenditure Survey (ENIGH) from 2006 to 2022 to describe the trends in food and beverage purchases by processing level for each outlet type for the general population, and by socioeconomic strata and urbanicity levels.

Data sources

We used nine rounds of the National Income and Expenditure Survey (Encuesta Nacional de Ingresos y Gastos de los Hogares, ENIGH): 2006, 2008, 2010, 2012, 2014, 2016, 2018, 2020, 2022. We selected these years because the distinction of outlets according to their fiscal regime prior to 2006 was not as detailed, limiting our understanding of the healthfulness of food and beverage purchasing patterns in the informal, mixed, and formal food sector.

The survey is conducted every two years by the National Institute of Statistics and Geography of Mexico (INEGI), with every round of the survey being representative at the national level. Starting in 2016, the survey also became representative at the state level. ENIGH collects information on household income and expenditure, sociodemographic characteristics, characteristics of the household members, among others [23]. Households’ information on daily expenses in ENIGH was collected for seven consecutive days. Household expenditure in foods and beverages was reported by the household member responsible for the purchases. Additionally, each member of the household kept a food diary. The food diary included the name of the food/beverage, quantity purchased (liters or kilograms), the price paid (MXN), and the food outlet where purchases happened [23].

In rounds 2006 to 2022, ENIGH included a total of 430,545 households with a variability of 20,330 households in 2006 to 90,102 in 2022. We excluded households that did not report purchases on food or beverages, and households that only reported purchases in restaurants, cafés, bars, and low-budget restaurants (n = 5,461, 1.27%), given that we do not know what was purchased. The number of households that reported food purchases by food outlet can be found in Additional File 1. The final analytical sample included 425,084 households.

Food and beverage outlets

Over the years, ENIGH has categorized Mexico’s food and beverage outlets differently. In 2006 and 2008, ENIGH classified outlets in 15 categories: public markets; street markets (tianguis); street vendors; small neighborhood stores (abarrotes); specialty stores; low-budget restaurants; restaurants, cafes, bars; chain convenience stores; supermarkets; department stores; membership stores; purchases out of the country; and others. Starting in 2010 and up to 2022, ENIGH added four new outlets: acquaintances; internet purchases; and two government food establishments, Diconsa and Liconsa.

Considering that food outlet categorization varied over time, we classified outlets into 9 mutually exclusive categories (Table 1): 1) street markets (tianguis); 2) street vendors; 3) acquaintances; 4) public markets; 5) specialty stores; 6) small neighborhood stores (abarrotes); 7) supermarkets; 8) chain convenience stores; and 9) others. Others include food outlet categories that individually accounted for a small percentage of the total food and beverage expenditure (< 1%). Since ENIGH does not specify the fiscal regime of the food outlets, we categorized the food outlets as informal, mixed, and formal according to their type [18,19]. The informal sector, defined as outlets that are not registered or regulated by fiscal laws, included street markets, street vendors, and acquaintances. The fiscally mixed sector included public markets, specialty stores, and small neighborhood stores given that these outlets could be fiscally unregulated or regulated. The formal sector, defined as outlets that are fiscally regulated, included supermarkets and chain convenience stores.

Table 1

Food and beverage outlet classifications and their characteristics.
Food Outlet	Characteristics	Fiscal Regime
Street markets (tianguis)	An open-air market that is traditionally held on certain market days in the streets of a town or city neighborhood.	Informal
Street vendors	Stands in public roads or spaces, vendors from home to home, and vehicles that offer goods or services (mobile vendors) are considered street vendors.	Informal
Acquaintances	People dedicated to the sale of products and food that do not have a fixed establishment. They sell foods to neighbors, friends, family, or workplaces.	Informal
Public markets	Public space where retail sales take place in different fixed establishments	Mixed
Specialty stores	Outlets that are dedicated to the commercialization of a single product or service: fruit and vegetable shops, chicken shops, tortilla shops, butcher shops, among others.	Mixed
Small neighborhood stores (abarrotes)	Outlets dedicated to the retail sale of various products (grocery stores or ‘mom and pop’ stores)	Mixed
Supermarkets	Large commercial stores, divided into specialized departments, by items or products and have self-service for the public (Walmart, Soriana, etc).	Formal
Chain convenience stores	Commercial chains that sell food products, packaged snacks and cookies, soft drinks, bottled water, alcoholic beverages, among others. These outlets are less than 500 m², with > 18 business hours, and open 365 days a year. (e.g., 7-eleven, Oxxo).	Formal
Others	Wholesalers, department stores, international purchases, government establishments that provide food, and internet purchases (included from 2010 onwards).	Formal

Processing level of food and beverage purchases

We used the processing level of foods and beverages according to the NOVA classification criteria [24] as a reference measure of the healthfulness of food purchases. Since 2006, food and beverages in ENIGH have been classified into 247 items, of which 234 items were classified according to their processing level (Additional File 2). The excluded items were purchases of food for animals, tobacco-related products, expenses related to food preparation and food provided by the government. We classified the 234 items as: 1) unprocessed and minimally processed foods, including foods that have not been transformed in any way, such as fresh fruits, vegetables, legumes, grains, and unprocessed meat; 2) processed culinary ingredients, including ingredients used to add flavor to food, such as oils, fats, salt, sugar, and spices; 3) processed foods, including foods that go through a transformation process like canned, cured, and smoked; and 4) ultra-processed foods, which are products manufactured from highly complex industrial procedures and have added sweeteners, flavors, and other additives. Some examples include sugary drinks, packaged snacks, and candy.

Education and urbanicity

We used the highest education level of the head of the household as a proxy for the household's socioeconomic status. Education was used instead of income because income was collected differently over the years. ENIGH considers eleven categories of education level: 1) without formal education, 2) preschool, 3) incomplete primary school, 4) complete primary school, 5) incomplete middle school, 6) complete middle school, 7) incomplete high school, 8) complete high school, 9) incomplete professional degree, 10) complete professional degree, 11) postgraduate degree. For this analysis, we grouped them into 4 mutually exclusive categories: 1) without formal education (1); 2) preschool or primary school (2 to 5); 3) middle school or high school (6 to 9); and 4) higher education (10 to 11).

Urbanicity is defined by the National Institute of Statistics and Geography of Mexico according to the number of inhabitants: 1) rural areas are those with less than 2,500 inhabitants; 2) small cities include localities with a population between 2,500 and 14,999 inhabitants; 3) medium-sized cities are those with a population between 15,000 to 99,999 inhabitants; and 4) large cities (metropolitan cities) include localities with more than 100,000 inhabitants [23].

Statistical analysis

For every survey year, we estimated the percentage of food and beverage expenditure (hereafter purchases) by processing level for each outlet for the overall population and stratifying by education and urbanicity. For a hypothetical example, results should be interpreted as follows: for a given household, out of every $100 MXN spent in street vendors, 80% were spent on minimally processed foods, and 20% of ultra-processed foods. Households that did not report food or beverage expenses in a specific outlet were excluded from the analysis. All analyses were conducted in Stata 16 using the SVY command to account for the complex survey design and weighed to generate nationally representative estimates. Weights were created for every ENIGH survey to account for the selection probabilities and survey non-response to match the estimated population for every survey year from the National Institute of Statistics and Geography [23].

Table 2 shows the sociodemographic characteristics of households which reported food and beverage purchases in the ENIGH surveys from 2006 to 2022. The proportion of households without formal education and primary school decreased over time, while households with high school and higher education levels increased from 2006 to 2022. The proportion of households living in rural areas slightly increased from 2020 to 2022.

Table 2

Households’ sociodemographic characteristics: the National Income and Expenditure Survey, 2006–2022.
Year	2006	2008	2010	2012	2014	2016	2018	2020	2022
Total households (N)	20,330	29,042	27,224	8,854	19,266	69,476	73,838	87,970	89,102
Education level, % a
Without formal education	9.9	9.4	9.0	9.0	7.7	7.1	6.7	6.3	5.7
Preschool/primary school	57.0	44.7	42.6	40.0	38.1	36.3	34.5	33.6	32.0
Middle/high school	22.1	35.1	36.7	39.8	41.5	43.6	45.0	46.0	47.0
Higher education	10.9	10.8	11.8	11.3	12.7	13.0	13.8	14.0	15.3
Urbanicity, %
Rural areas	22.3	21.4	21.4	22.0	22.0	21.7	23.1	21.5	23.0
Small cities	13.2	13.8	13.8	13.3	13.5	13.9	14.1	13.7	13.9
Medium-sized cities	14.7	14.5	14.4	14.4	14.8	14.5	14.7	14.9	14.6
Metropolitan cities	49.8	50.3	50.4	50.3	49.8	49.9	48.1	49.9	48.5
a. education level of the head of the household

Trends in food and beverage purchases by food outlet

Figure 1 shows the proportion of food purchases (% of the total expenditure) by food outlet type at the beginning (2006) and end (2022) of the study period. In 2006, 73.5% of food purchases among Mexican households went to mixed food outlets. The same year, formal outlets accounted for 13.1% of the total food purchases and informal outlets 11.9%. In 2022, the proportion of purchases from the mixed sector was similar, but we observed changes by outlet type: public markets and small-neighborhood stores decreased by 3.3 percentage points (p.p.) and 4.2 p.p., respectively, while the proportion of purchases from specialty stores increased (+ 5.8 p.p.). Food purchases in formal outlets showed stability in supermarkets over time and an increase in chain convenience stores (+ 1.1 p.p.). Regarding the changes in food purchases in informal outlets, by 2022, there was a decrease of 2.1 p.p. in street vendors, while purchases at street markets remained stable over time. Information on acquaintances was included in ENIGH starting 2010, when food purchases in these outlets accounted for 2.1% of the total purchases and showed a slight increase of 0.6 p.p. by 2022.

Figure 1. Proportion of food and beverage purchases (% of the total purchases) by outlet type in 2006 and 2022, ENIGH. *Acquaintances are included in ENIGH from 2010 onwards. Informal outlets (orange) include street vendors, street markets, and acquaintances; mixed outlets (green) include public markets, specialty stores, and small neighborhood stores; formal outlets (purple) include supermarkets, and chain convenience stores. Other stores (blue) include wholesalers, department stores, international purchases, government establishments that provide food, and internet purchases.

Trends in food and beverage purchases by processing level and by food outlet

Figure 2 shows the proportion of purchases (% of expenditure) of foods and beverages of different processing levels by food outlet type at the beginning (2006) and end (2022) of the study period. Yearly purchases can be found in Additional file 3. In 2006, the outlets with the highest proportion of minimally processed foods purchases were street markets (83.3%), public markets (80.6%), specialty stores (74.6%), and street vendors (69.5%). In contrast, the highest percentage of ultra-processed foods was purchased at chain convenience stores (48.6%), small neighborhood stores (37.3%), and supermarkets (35.3%). By 2022, purchases of minimally processed foods decreased by 4.8 p.p. in acquaintances, 6.2 p.p. in chain convenience stores and 7.9 p.p. in street vendors. Street markets, public markets and specialty stores only presented a slight decrease in the purchases of these products. These decreases were accompanied by an increase in processed food purchases in specialty stores (+ 3.3 p.p.), acquaintances (+ 4.8 p.p.) and street vendors (+ 6.8 p.p.). In contrast, ultra-processed food purchases decreased by 3.1 p.p. in small neighborhood stores, and 8.1 p.p. in supermarkets; and purchases of minimally processed foods increased 5.2 p.p. in supermarkets. The proportion of ultra-processed food purchases remained stable at chain convenience stores.

Figure 2. Proportion of food and beverage purchases by processing level and outlet type in 2006 and 2022, ENIGH. The values on the right show the distribution of household food and beverage purchases by type of food outlet in 2006 and 2022. Informal outlets (orange) include street vendors, street markets, and acquaintances; mixed outlets (green) include public markets, specialty stores, and small neighborhood stores; formal outlets (purple) include supermarkets, and chain convenience stores. Other stores (blue) include wholesalers, department stores, international purchases, government establishments that provide food, and internet purchases.

Trends in food and beverage purchases by processing level and by food outlet, stratified by education

Figure 3 shows the changes over time in households' food purchases by processing level and by food outlets, stratified by education level of the head of the household. Percentage data from 2006 to 2022 by processing level are available in Additional file 4. The proportion of food purchases by processing level across the different education levels were similar to the ones observed in the overall sample; however, households without formal education had higher purchases of minimally processed foods in food outlets, compared to households with higher education. Households without formal education increased their purchases of minimally processed foods in specialty stores (+ 3.6 p.p.) and had a decrease in purchases of minimally processed foods in chain convenience stores (-20.5 p.p.), acquaintances (-7.0 p.p.), street vendors (-5.4 p.p.), and public markets (-2.5 p.p.). These households also decreased their purchases of ultra-processed foods in supermarkets (-3.8 p.p.), and chain convenience stores (-13.3 p.p.), but increased their purchases of processed foods in chain convenience stores (+ 19.7 p.p.), and street vendors (+ 5.9 p.p.).

Households with higher education increased their purchases of minimally processed foods in supermarkets (+ 4.8 p.p.) and small neighborhood stores (+ 3.0 p.p.) and decreased their purchases of minimally processed foods in street vendors (-16.4 p.p.). Households with higher education also decreased their purchases of ultra-processed foods in supermarkets (-6.5 p.p.), small neighborhood stores (-7.1 p.p.), and specialty stores (-2.9 p.p.), and increased purchases of ultra-processed (+ 4.5 p.p.) and processed (+ 11.9 p.p.) foods in street vendors. In chain convenience stores, these households increased their ultra-processed foods purchases by 2.9 p.p. and decreased in minimally processed foods by 3.6 p.p.

Figure 3. Trends in the proportion of food and beverage purchases by processing level in the informal, mixed, and formal sector, stratified by education, ENIGH 2006, 2022. A) Without formal education; B) Higher education. Informal outlets (orange) include street vendors, street markets, and acquaintances; mixed outlets (green) include public markets, specialty stores, and small neighborhood stores; formal outlets (purple) include supermarkets, and chain convenience stores. Other stores (blue) include wholesalers, department stores, international purchases, government establishments that provide food, and internet purchases.

Trends in food and beverage purchases by processing level and by food outlet, stratified by urbanicity

Figure 4 shows the changes over time in households' food purchases by processing level and by food outlets, stratified by urbanicity. Percentage data from 2006 to 2022 by processing level are available in Additional file 5. The proportion of food purchases by processing level in rural localities and cities were similar to the results described for the overall sample. Households residing in rural localities increased their purchases of minimally processed foods in supermarkets (+ 4.6 p.p.), chain convenience stores (+ 5.0 p.p.), and specialty stores (+ 3.3 p.p.), and decreased their purchases of minimally processed foods in street vendors (-3.8 p.p.), acquaintances (-3.7 p.p.) and public markets (-3.0 p.p.). Households residing in rural localities decreased their purchases of ultra-processed foods in supermarkets (-8.4 p.p.) and chain convenience stores (-16.9 p.p.), and increased purchases of processed foods in chain convenience stores (+ 5.3 p.p.) and street vendors (+ 3.3 p.p.).

Households residing in metropolitan cities increased their purchases of minimally processed foods in supermarkets (+ 4.9 p.p.) and decreased their purchases of minimally processed foods in street vendors (-10.2 p.p.), chain convenience stores (-6.6 p.p.) acquaintances (-5.6 p.p.), and specialty stores (-4.5 p.p.). These same households decreased their purchases of ultra-processed foods in supermarkets (-7.5 p.p.) and small neighborhood stores (-4.2 p.p.) and increased their purchases of ultra-processed foods only in chain convenience stores by 4.2 p.p.

Figure 4. Trends in the proportion of food and beverage purchases by processing level in the informal, mixed, and formal sector, stratified by urbanicity, ENIGH 2006, 2022. A) rural localities; B) metropolitan cities. Informal outlets (orange) include street vendors, street markets, and acquaintances; mixed outlets (green) include public markets, specialty stores, and small neighborhood stores; formal outlets (purple) include supermarkets, and chain convenience stores. Other stores (blue) include wholesalers, department stores, international purchases, government establishments that provide food, and internet purchases.

Using repeated cross-sectional data from household purchases, we provide a deep understanding of the healthfulness of foods and beverages purchased over time across the mixed, informal, and formal food sectors for the Mexican population and for different education and urbanicity strata. Over time, the proportion of purchases of minimally processed foods was higher in street markets, street vendors, public markets, and specialty stores. In contrast, the highest percentage of ultra-processed foods was purchased at chain convenience stores, small neighborhood stores, and supermarkets. However, food purchases became healthier in supermarkets and less healthy in street vendors, chain convenience stores and acquaintances. Yet, when we consider the contribution of each of these outlets to the total food purchases in Mexico, small neighborhood stores have represented the outlets where most of the ultra-processed foods were purchased over time and specialty stores where the ones where most of the minimally processed foods were purchased.

Our study shows that food purchases from the informal food sector have historically been mostly healthy, especially purchases from street markets. The informal sector has also provided healthy food options across all income strata, being most prevalent within the most socioeconomically disadvantaged groups. However, there has been a shift towards less healthful purchasing patterns in street vendors and acquaintances. In street vendors, the decrease in purchases of minimally processed foods was greater among households with higher education and households living in metropolitan cities. Minimally processed foods from acquaintances decreased among households with lower education and those living in both rural and metropolitan areas. Recent studies from other countries of the global south have found that purchases from informal vendors are characterized by fruits and vegetables and low purchases of ultra-processed foods [25,26]. However, previous research has also reported that street foods not only offer minimally processed foods, but also ultra-processed foods that contribute significantly to total daily energy intake [27]. Studies from urban areas in Mexico have also documented that street vendors have the tendency to offer ultra-processed foods and beverages [6,28], showing that street food stands are a source of both unhealthy and healthy foods for communities across neighborhoods in Mexico City [29]. Since the informal food sector is deeply rooted in Mexican culture [30] and unlikely to disappear [5], we have to acknowledge the role that the informal food sector plays across different food environments.

Trends in the healthfulness of purchases from the mixed sector were heterogeneous. Purchases in small neighborhood stores became healthier over time among households with higher education and those living in metropolitan areas. Household food purchases in public markets and specialty stores have been mostly represented by minimally processed foods over time. However, households in metropolitan areas had a noticeable decrease in their minimally processed food purchases in specialty stores, whereas the opposite was observed in rural areas. Specialty stores are not only one of the outlets where healthier purchases are made, the purchases in these outlets have also increased over time [19]. Even though purchases in public markets have remained healthy over time, the proportion of total food purchases from public markets has decreased over time, particularly among households with less education and residing in rural localities [19]. Despite finding that the proportion of purchases of ultra-processed foods in small neighborhood stores has decreased over time, these outlets have accounted for the greatest proportion of food purchases in Mexico (~ 30%) [18,19], making small neighborhood stores the outlets where people purchase the majority of ultra-processed foods. In line with our results, the study by Ortiz-Hernández (2022) using data from 2018 found that specialized stores and public markets were key sources of fresh food and an important food supply for poorer households. Also, recent studies from Mexico have found a positive association between higher densities of specialty stores with higher purchases of fruits and vegetables, lower purchases of ultra-processed foods and better health outcomes [9,31]. These same studies found that higher densities of small neighborhood stores were associated with lower purchases of fruits and vegetables and worse health outcomes [9,31]. These results reveal the importance of considering the urban context in which we study the retail food environment and how purchases in food outlets vary.

Food outlets in the formal sector have been an important source for unhealthy food purchases in Mexican households. While food purchases from chain convenience stores have remained unhealthy, purchases from supermarkets shifted towards healthier foods. This improvement happened across all education and urbanicity levels, but it was greater among households with higher education and those living in metropolitan cities, which represent the households with the most purchases in formal food outlets [18,19]. Moreover, it is relevant to emphasize that even though the number of supermarkets and chain convenience stores has increased over the years [32–35], these outlets have represented around 10% and 1% of the total food purchases over the last decade, respectively [18,19].

This analysis sheds light on the complexity of the retail food environment in Mexico, showing that there is no clear categorization of healthy and unhealthy food outlets. It is crucial to recognize the myriad of food outlets that compose the retail community food environment and the quality of foods bought in each type of outlet. Although most research tends to focus on the formal food sector, we bring into question the quality of food across a wider categorization of formal and informal food outlets and if there have been variations over time. Given these findings, our recommendation is to avoid characterizing outlets as healthy or unhealthy and to avoid aggregate measures of food environment healthfulness like the Retail Food Environment Index (RFEI). Such measures – which have largely been developed and used in the global north – typically classify food retailers of a given type (e.g., supermarkets) as either healthy or unhealthy [36]. Based on our findings, future studies could weigh the healthfulness of outlets based on the percentage of quality of purchases (Additional file 3).

Given that our understanding of the retail food environment mostly comes from the global north, food policy has focused on formal retailers, ignoring the role of the informal and mixed food sector [37,38]. Studies focusing on these sectors are very scarce, and little direction has been provided on how to engage them to improve the nutritional quality of the foods being sold. The governmental response to the informal food sector has been to repress or ignore it, rather than facilitating their registration and identifying routes of engagement through incentives and reduced punitive actions [39]. Prior analyses suggest that direct engagement is needed to reduce food insecurity and harness the nutritional potential of informal food venues, particularly for the poorest sectors of the population [3]. For instance, in India, researchers suggested the possibility of issuing food vouchers to buy food from street vendors. Such a program would serve three purposes: incentivize the local economy, condition voucher reception to minimal standards of hygiene and nutritional quality and initiate competition across food vendors based on affordability, diversity, and quality [40]. Policies to maintain or increase the healthfulness of the informal and mixed sectors could be implemented all along the food supply chain, but further research is needed to understand specific opportunities in the global south. One example to be led by local governments is to support markets financially and structurally by improving their maintenance, hygiene, making them more spacious, and implementing an adequate infrastructure for food conservation; characteristics that are usually lacking in these spaces [41]. Reshaping the retail food environment to promote healthy diets will require experimentation with a range of policy options that act across the food system, from producers to processors, distributors, retailers, and consumers [37].

Our study is not without limitations. The ENIGH surveys do not classify the food outlets by fiscal regime. Thus, we were not able to determine whether a specific mixed store tends more towards a formal or an informal establishment. However, we described the healthfulness of food purchases by outlet type over time, which provides information regarding the changes in the food purchasing patterns in each outlet at a national, urbanicity and educational level. A limitation regarding the timeframe of our study is that we were not able to see changes in the healthfulness of food purchases prior to 2006. Therefore, we cannot see the changes in the quality of food purchases in the different outlets during the late 90s, when the modernization of the retail food environment began. Our study did not consider the role that food prices and diversity of outlets play in food purchasing choices, which should be included in future studies. We excluded from the analysis foods that were consumed away from home or wasted. Purchases of foods consumed away from home are defined as breakfast, lunch, and dinner meals in ENIGH, representing on average, 16% of purchases from street vendors and 11% from acquaintances and are an important source of urban food provisioning. Given the difficulties of quantifying these foods, more research is needed focusing on the nutrition quality of the informal food sector [5]. It is also important to acknowledge that purchases do not equate to consumption. We were not able to account for food waste from households’ food and beverage volume records. However, the nutritional profile of purchases is highly correlated with diet quality as measured by 24-h recalls and therefore a good representation of overall intake [42], particularly when ENIGH enumerators carefully supervised the responses every day from the 7-day data collection [23]. Lastly, purchases in some outlets might be underestimated since some purchases are unplanned and households may not report them.

Food environment research from the global north is not transportable to the global south. Despite the penetration of formal stores (i.e., supermarkets and chain convenience stores), these are not the major sources of food for Mexican households. To promote healthier food environments, policymakers must pay closer attention to where the largest proportion of food purchases is being made (i.e., small neighborhood, specialty stores), and where the healthiest purchases are happening (i.e., street markets, public markets, and specialty stores). It is also important to intervene in the stores where most ultra-processed foods are being purchased (i.e., small neighborhood stores, supermarkets, and chain convenience stores). Furthermore, it is important that policymakers consider the historical context of the food environment in Mexico, particularly trends in spending levels across different types of retailers, the healthfulness of purchases within each type of retailer, and understand the reasons why purchases from certain food outlets are becoming healthier, while others are becoming less healthy.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Availability of data and materials

The datasets generated and/or analyzed during the current study are available in the INEGI-ENIGH repository, https://www.inegi.org.mx/programas/enigh/nc/2022/

Competing interests

The authors declare that they have no competing interests

Funding

The Salud Urbana en América Latina (SALURBAL)/ Urban Health in Latin America project is funded by the Wellcome Trust [205177/Z/16/Z].

Authors' contributions

AD-B conducted the statistical analysis. AD-B, IF and DS designed the study, interpreted the results, and led the writing. NL-O, CP-F, YR-T, BAL, MAC, JAR and TB-G contributed to the interpretation of results and critical review of the manuscript. All authors read, edited, and approved the final version of the manuscript.

Acknowledgements

The authors acknowledge the contribution of all SALURBAL project team members. For more information on SALURBAL and to see a full list of investigators see https://drexel.edu/lac/salurbal/team/

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Changes in the healthfulness of food and beverage purchases from 2006 to 2022 in formal, mixed, and informal outlets in Mexico

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Abstract

Background

Methods

Results

Conclusions

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BACKGROUND

METHODS

Data sources

Food and beverage outlets

Processing level of food and beverage purchases

Education and urbanicity

Statistical analysis

RESULTS

Trends in food and beverage purchases by food outlet

Trends in food and beverage purchases by processing level and by food outlet

DISCUSSION

CONCLUSIONS

Declarations

References

Additional Declarations

Supplementary Files

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Version 1