key: cord-0984942-fe1adcjg
authors: Della Valle, Petra Giulia; Mosconi, Giansanto; Nucci, Daniele; Vigezzi, Giacomo Pietro; Gentile, Leandro; Gianfredi, Vincenza; Bonaccio, Marialaura; Gianfagna, Francesco; Signorelli, Carlo; Iacoviello, Licia; Odone, Anna
title: Adherence to the Mediterranean Diet during the COVID-19 national lockdowns: a systematic review of observational studies
date: 2021-10-01
journal: Acta Biomed
DOI: 10.23750/abm.v92is6.12233
sha: c2704859d452bc49190a15199fcf9ada44b20c21
doc_id: 984942
cord_uid: fe1adcjg

BACKGROUND AND AIM OF THE WORK: During the COVID-19 pandemic, many countries adopted restrictive measures to mitigate infection spread, which might have influenced people’s lifestyle and dietary habits. We conducted a systematic review to evaluate the impact of national lockdowns on adherence to the Mediterranean Diet (MD). METHODS: Studies were identified searching Medline, Embase, Web of Science, and the Cochrane Library. Studies published until 4(th) May 2021 were included. We only considered studies reporting original data from quantitative analysis and assessing changes in adherence to the MD, using validated dietary scores, or in consumption of MD food items. Data extraction, pooling, and quality appraisal of included studies were conducted following the PRISMA guidelines. RESULTS: Forty-two studies were retrieved. After screening, 12 studies met inclusion criteria and were included in the review, of which 4 (33%) were longitudinal studies. Six (85.7%) of the seven studies that measured changes in MD adherence before-during lockdown reported an increase (rate of change of high-adherence to MD ranged between +3.3% and +21.9%). Evidence indicates that consumption of MD food items increased during lockdown but is heterogeneous in study design, quality, and findings. CONCLUSIONS: Our results suggest adherence to the MD during lockdown might have increased in some settings, while the determinants of such a trend are to be further explored. We raise awareness of the need to research further the impacts and long-term consequences of COVID-19 containment measures on dietary and lifestyle habits. (www.actabiomedica.it)

The term "Mediterranean Diet" (MD) describes the traditional eating habits of people living in olivegrowing areas and, more generally, in the territories around the Mediterranean Sea (1, 2) . The MD is traditionally characterized by a predominant consumption of vegetables, fruit, legumes, whole grains, nuts, seeds, and fish, with olive oil as the main source of added fats, small amount and low-frequency consumption of meat (especially if red and processed), a moderate consumption of dairy products, and a moderate intake of alcoholic beverages, mainly red wine during meals (3) (4) (5) . In 2010, the MD was recognized by UNESCO as a Cultural Heritage of Humanity (6) . Non-communicable diseases such as cancer, cardiovascular disease (CVD), type 2 diabetes, and obesity are the leading cause of death worldwide and account for 70% of all deaths in Europe each year (7) . It has been shown that these diseases are largely preventable by promoting healthy lifestyles, such as moderate alcohol consumption, physical activity, tobacco cessation, and healthy diets (8) (9) (10) . The MD is commonly accepted as a likely dietary model for the prevention and control of chronic non-communicable diseases throughout life, and the protective effect of the MD against these diseases has been accurately reported by many studies (8, (11) (12) (13) . However, globalization and cultural and social changes in recent years have profoundly influenced people's lifestyles, causing in most regions of the world a gradual decrease in adherence to the MD (14-16) and a simultaneous shift towards the western dietary pattern, particularly in the countries of the Mediterranean basin themselves, and in younger age groups (5, (17) (18) (19) . During the COVID-19 pandemic, several containment measures such as the closure of schools, restaurants, cinema, gyms, shopping centers, cancellation of public events, up to the establishment of curfews, partial and complete lockdowns, were adopted to mitigate the spread of the disease (20) (21) (22) These containment measures have undoubtedly caused changes in people's lifestyle (23) , influencing their levels of alcohol consumption (24) , smoking (25, 26) , other addictions (27, 28) , physical activity (29) , and, indeed, their dietary habits (30) . In parallel, the COVID-19 pandemic is having a severe impact on the global economy, determining the worst recession since World War II (31) , and the availability of material resources has been already identified as a strong determinant of adherence to the MD (32) . As the available evidence is scarce and often conflicting, the purpose of this systematic review is to analyze and summarize recently published studies to assess the impacts and effects of lockdowns periods imposed to contain the COVID-19 outbreak on general population adherence to the MD.

The review's methods were defined in advance following the Prepared Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines (33) . The study protocol was registered with PROSPERO at http://www.crd.york.ac.uk/Prospero/ on the 8 th February 2021 (CRD42021232913).

Studies were identified by searching the electronic databases PubMed/MEDLINE, Embase and Web Of Science, and Cochrane Library. The search strategy was first developed in PubMed using a combination of free text and Mesh terms referring to i) the COVID-19 pandemic, ii) containment measures and stay-at-home orders (i.e., lockdown), and iii) the Mediterranean Diet. The search strategy was then adapted for use in the other databases. Complete search strategies are available in Appendix B. Further studies were identified from consultation with experts in the field and reference listing of relevant articles. Studies published up to 4 th May 2021, regardless of language, were included. We only considered for inclusion studies reporting original data from quantitative analysis. We excluded opinion papers (i.e., editorials, commentaries, and letters to the Editor) not providing original data. Only the studies considering the general population, regardless of age, were included (Appendix A).

We considered the following outcomes: i) rate of change in adherence to MD, assessed through validated dietary scores, and ii) rate of change in the consumption of specific food items that are typically attributable to the MD during COVID-19 related lockdown periods.

Identified studies were independently reviewed for eligibility by three authors (PGDV, DN, GM) in a two-step process; a first screening was performed based on title and abstract, while full texts were retrieved for the second screening. At both stages, disagreements were resolved through discussion with a senior researcher (AO). Data from selected articles were extracted and tabulated in a standardized pre-pi-loted form independently by two researchers (PGDV, GM), supervised by a third and a fourth author (DN, AO), in order to evaluate the quality of the studies and the synthesis of the evidence. Extracted data included: study design, country of study implementation, study period, study population, study setting, sample size, data collection method and timing, outcomes, measurements used to assess MD adherence, and changes in consumption of specific food items reported as, but not limited to, prevalence, mean, median, mean difference, or percentage.

The quality of the included studies was determined using the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies from the National Heart, Lung, and Blood Institute by two authors (PGDV and GM). Disagreements were resolved by consensus.

Fifty-seven records were identified by searching the selected electronic databases and identified data sources. After duplicates removal, titles and abstracts of 27 records were screened. Ten studies were excluded because they were not relevant to the research question, while the other 17 were assessed for eligibility. After second screening by full-text, 12 studies were included in the systematic review. A flow diagram of the screening and selection process is reported in Figure 1 .

The characteristics of the included studies are reported in Table 1 . Most of the studies were conducted in Spain (n=5, 41.7%) (34) (35) (36) (37) (38) , while 2 were conducted in Croatia (39, 40) , 1 in Iraq (41), 1 in Denmark (42) , 1 in Cyprus (43), 1 in Italy (44) , and 1 in Kosovo (45) . All included studies were in English, except one, which was published in Spanish (38) . Ten (83.3%) studies (36) (37) (38) (40) (41) (42) (43) (44) (45) focused on the general adult population, while one (35) (8.3%) focused on underage (<18 years old) students, and another (39) (8.3%) on both adults and underage students. Eleven (34, (36) (37) (38) (40) (41) (42) (43) (44) (45) out of twelve studies recruited convenience samples. Only one study (35) used stratified sampling. Eight studies (66.7%) had a cross-sectional design (36, 37, (39) (40) (41) (42) (43) 45) , while 4 (33.3%) were longitudinal studies (34, 35, 38, 44) . In three-quarters of the studies (n=9, 75%) (34, 36-38, 40-43, 45) data collection took place only during national lockdown periods and was conducted exclusively through an online survey. In the study by Dragun et al. (39) , a first data collection was conducted prior to the pandemic through a paper and pencil form, while a second survey, which took place during the lockdown, was conducted using an online survey. Medrano et al. (35) used an online questionnaire to collect data both before the pandemic and during the lockdown. Finally, Ruggero et al. (44) analyzed data from a telephone interviews-based longitudinal study that began before the pandemic and ended during the lockdown, and from a cross-sectional study conducted during the lockdown. Study enrollment periods ranged from 12 days (42) to 2 years (39). In half of the studies data were collected only once during lockdown periods (36, (40) (41) (42) (43) 45) . In four studies (34, 35, 39, 44 ) (33.3%), data collection took place both before the COVID-19 and during the lockdown period. Sánchez-Sánchez et al. (37) collected data dur- (43) reported that, during the lockdown, the median of the MEDAS scores remained unchanged (6.0 vs 6.0). However, the interquartile range had increased (2.0 vs 3.0); furthermore, in 31.9% of the participants, the MEDAS score referring to the lockdown period was found to be higher than the score referring to the previous period, while in 22.7% of participants it was found to be lower. Medrano et al. (35) found that, in their sample, the mean score on the KIDMED (48) questionnaire had increased during the lockdown compared to the previous period from 5.9±1.8 to 6.4±1.5 (p<0.02); they also reported that the percentage of participants participants with a KIDMED questionnaire score of less than 8 (thus those whose MD adherence can be considered low) had decreased from 81.1% to 76.4% during lockdown (p=0.476). Rodríguez-Pérez et al. (36) asked the participants to fill in the MEDAS questionnaire reporting their eating habits both during the lockdown and in the previous period. First, they found that, during the lockdown, the mean score was higher (6.53±2.0 to 7.34±1.93, p<0.001) compared to the previous period. Furthermore, considering the lockdown period, the average score of the participants who had scored at least 9 points was 9.8 (SD=0.9, p<0.001), while the mean of the scores that these same participants obtained by answering about their eating habits in the previous period was 8.7 (SD=1.6, p<0.001). For those whose lockdown period scores were above 6, but below 9 points, the average score was 7.0 (SD=0.8, p<0.001), while the average score obtained when considering the answers they gave referring to the previous period was 6.2 (SD=1.2, p<0.001). Finally, for those whose lockdown period scores were below 6, the average score was 4.5 (SD=0.7, p<0.001), while the mean score obtained when considering the answers they gave referring to the previous period was 4.2 (SD=0.9, p<0.001). Sánchez-Sánchez et al. (37) found the percentage of people with high adherence to the MD based on the score obtained in the MEDAS questionnaire (≥9 points) had increased by 3.3% during lockdown (from 4.7% to 8.0%, χ 2 =274.76, p<0.001). Tárraga Lopez et al. (38) found the percentage of people with high adherence to the MD based on the score obtained in the MEDAS questionnaire (≥10 points) had increased from the first week of lockdown to the fifth week of lockdown by 10.6% (from 77.3% to 87.9%, p=0.859). Furthermore, they reported that in the first week of lockdown, the average score was 10.03±1.9, while at the end of the fifth week it had increased to 10.47±2.1 (p<0.02).

Three studies (39, 41, 44 ) (25% of included studies) analyzed changes in cereal consumption during national lockdowns compared to earlier periods (table 3) . Results are conflicting: one study (39) (33.3%) found a decrease in cereal consumption, one study (44) (33%) found an increase (44) , and another study (33%) found no significant difference (41) . The consumption of legumes during national lockdowns compared to earlier periods was analyzed by eight studies (36, 37, 39-42, 44, 45) , 66.7% of the total (table 4): seven (36, 37, 39-41, 44, 45) (87.5%) of them found an increase in consumption, one (42) (12.5%) found a decrease. Six studies (36, 40-42, 44, 45) reported the percentage of people who had changed their consumption of legumes during the lockdown: the percentage of those who had increased it ranged from 7.1% to 14.9%, the percentage of those who decrease it ranged from 3.9% to 11.0%, while the percentage of those who maintained it stable ranged from 75.0% to 84.4%. Eight studies (36, 37, 39-42, 44, 45) , 66.7% of the total, looked at possible changes in vegetable consumption (table 5) : only one (42) (12.5%) found a decrease in consumption, while the other seven (36, 37, 39-41, 44, 45) (87.5%) found an increase. The percentage of participants who changed their vegetable consumption during national lockdowns was reported in seven studies (36, 39-42, 44, 45) : the percentage of participants who had increased it ranged from 11.3% to 50.0%, the percentage of those who decreased it ranged from 3.2% to 19.5%, the percentage of those who did not change their consumption ranged from 46.0% to 72.7%. Changes in fruit consumption during lockdown were investigated by eight studies (36, 37, 39-42, 44, 45) , 66.7% of the total (table 6). Fruit consumption during national lockdowns was found to have increased compared to previous periods in seven studies (36, 37, (42) study (12.5%) it was found to have decreased. In the seven studies reporting them (36, 39-42, 44, 45) , the percentage of people who declared they had increased their fruit consumption during the lockdown ranged from 11.1% to 60.1%, the percentage of people who declared they had decreased it ranged from 5.2% to 24.9%, while the percentage of people who declared they had not changed their consumption ranged from 25.5% to 72.0%. Four (37, 39, 41, 44) of the included studies (33.3%) looked for changes in nut consumption during national lockdowns (Table 7) : three (37, 41, 44) of these (75%) found an increase in consumption compared to previous peri-ods, while one (39) (25%) found a decrease in consumption. The percentage of participants who changed their nut consumption during national lockdowns was reported in two studies (41, 44) : the percentage of participants who had increased it ranged from 10.7% to 30.9%, the percentage of those who decreased it ranged from 5.8% to 13.3%, the percentage of those who did not change their consumption ranged from 55.8% to 83.5%. Eight (36, 37, (39) (40) (41) (42) 44 , 45) (66.7%) of the studies included in our systematic review looked at possible changes in meat consumption (table 8) . Two studies (36, 39 ) asked participants about their consumption of meat and processed meat in general during lockdown respect previous periods, and reported the percentage of those who had increased it, decreased it, or maintained it stable: their outcomes were conflicting since Dragun et al. (39) found the percentage of those who had increased their consumption was higher than the percentage of those who had decreased it (12.1% vs 8.5%), while Rodríguez-Pérez et al. (36) found an opposite result (7.0 vs 21.7%). Two studies assessed changes in consumption of white meat and found different results (39, 44): Dragun et al. (39) found it had decreased, while Ruggero et al. (44) found it had increased. Of the seven studies investigating the consumption of red meat (37, 39-42, 44, 45) , five (39, 40, 42, 44, 45) 37, 40, 44, 45) found that it had increased (71.4%). In the five studies (36, 40, 42, 44, 45) that assessed them, the percentage of participants who had increased their consumption ranged between 5.5% and 23.0%, the percentage of participants who had decreased their consumption ranged between 1.3% and 11.5%, while participants who had not changed their consumption ranged between 67.0% and 88.8 %. Eight studies (37, 39-42, 44, 45) (66.7% of the included studies) assessed changes in fish consumption during national lockdowns compared to previous periods (table 12) : four (40, 41, 44, 45) (50%) of them reported a decrease in fish consumption, the other four (36, 37, 39, 42) (50%) reported a decrease in fish consumption. Four studies (36, 40, 42, 45) reported the percentage of people who had changed their consumption of fish in general (both fresh and frozen seafood, and fresh, canned, frozen or dried fish) during national lockdowns: the percentage of those who had increased it ranged from 7.2% to 15.8%, the percentage of those who decrease it ranged from 8.4% to 20.4%, while the percentage of those who maintained it stable ranged from 72.0% to 75.8%. Finally, six studies (36, 37, (40) (41) (42) 45) (50% of included studies) assessed changes in consumption of alcoholic beverages in general, or specific alcoholic beverages (wine and beer) during national lockdowns compared to previous periods (table 13) . Four studies (36, 40, 42, 45) reported the percentage of people who had changed their consumption of alcoholic beverages in general: two (36, 42) (50%) found it had increased, while the other two (40, 45) (50%) found it had decreased; specifically, in these studies the percentage of those who had increased it ranged from 4.0% to 57.3%, the percentage of those who decrease it ranged from 10.4% to 43.0%, while the percentage of those who maintained it stable ranged from 32.3% to 62.2%.

The quality assessment of included studies is reported in Table 1 . Quality was rated as "good" in 11 studies (28-34,36-39) (91.7%), "fair" in one (41) . We determined that most of the studies were susceptible to recall bias because participants were asked to remember what their diet was like before the lockdown. Since many studies were based on non-representative samples, the authors resorted to post-stratification.

The MD represents a valuable dietary model for the prevention and control of obesity (49) (50) (51) (52) , metabolic syndrome (11, 53) and related chronic non-communicable diseases (8, 12) ; however, in recent years, in most regions of the world, globalization and cultural and social changes have caused a progressive abandonment of it and a simultaneous shift towards the western dietary pattern (14) (15) (16) , which, on the contrary, has been associated with weight gain (54-56) and cardio-metabolic traits (57) (58) (59) . It is a matter of concern that this phenomenon is particularly pronounced in the countries of the Mediterranean basin themselves and in the younger age groups (5, 17, 18) . During the COVID-19 pandemic, several non-pharmacological interventions were adopted all around the world to mitigate the spread of the disease (20, 21) . These containment measures, especially national lockdowns, have undoubtedly caused changes in people's lifestyle (24, 25, 29) , also influencing their dietary habits (30, (60) (61) (62) (63) , although it is not yet clear whether and how they influenced adherence to the MD, as available evidence is scarce and conflicting. The possibility that adherence to the MD had decreased during national lockdowns would be worrisome since it could be a clue supporting the hypothesis that the COVID19 pandemic may have exacerbated other pre-existing "pandemics", such as obesity and metabolic syndrome (64) (65) (66) (67) (68) (69) (70) especially if this phenomenon were to continue even if these restraining measures were no longer necessary. The purpose of this systematic review was to analyze and summarize recently published studies to assess the impacts and effects of lockdowns periods on general population adherence to the MD and its determinants.

Overall, six (34) (35) (36) (37) (38) 43) out of the seven studies reporting a rate of change in adherence to the MD, assessed through the use of validated dietary scores, found an increase in the proportion of participants with high MD adherence during the national blocking periods compared to previous periods, while one (39) found a decrease. The results of our systematic review are consistent with other research suggesting that, during national lockdowns, people increased their intake of some healthy foods (e.g. fruit and vegetables and pulses), but may also have increased their intake of foods that should be consumed in moderation (71) (72) (73) (74) .

In fact, three (36, 37, 42) out of six studies (36, 37, (40) (41) (42) 45) found an increase in alcoholic beverages consumption, and two (37, 41) out of seven authors (37, 39-42, 44, 45) found an increase in red meat consumption. Among the studies considering the change of a central tendency measure of the scores obtained by the participants on a validated scale (35, 36, 38, 39, 43) , three (36, 38, 43) used the MEDAS, and one (35) used its version for children and youths, the KIDMED score; the fact that one (43) of these studies found that the median of the scores remained unchanged with an increased interquartile range (IQR), while the other three (35, 36, 38) found that the mean had increased, could suggest that those who had increased their score during lockdown were mainly those who already had high adherence. All the studies that assessed the rate of change in adherence to the MD using a validated scale were conducted in Mediterranean countries, i.e. those where the MD is most popular, but also those where there has been the most significant reduction in adherence to this dietary pattern since the second half of the 21st century (19) . All the authors found that the percentage of participants who had high compliance with the MD had increased during national lockdowns (34, 35, 37, 38) , with the exception of one conducted in Croatia, which reported a decrease (39) . It should be noted that the latter was the only ones to use the MDSS (47) instead of the MEDAS (46) (or its version for young people and children, the KIDMED score (48)) to determine adherence to the MD, even if, these instruments have shown considerable overlap (75) . Moreover, in the study by Kolokotroni et al. (43) the percentage of participants who increased their adherence to MD during the national lockdown was higher than the percentage of participants who decreased it (31.9% vs 22.9%). This is interesting as it shows an inversion of the negative trend observed so far in the literature (5, 19) . This observation suggests that most people living in Mediterranean countries may have increased their adherence to MD during national lockdowns. As emerges from our data, lockdowns might have differentially impacted adherence to MD based on the study populations. For example, in the Dragun et al. study (39) , the sample included both underage and adult students and, during the lockdown, adherence to MD seemed to have decreased, especially in adult international students, who constituted 10.9% of the subsample that participated in the survey that was conducted before the pandemic and 11.1% of the subsample that participated in the survey that was conducted during the national lockdown. The authors attempted to explain their findings by stating that, in comparison to domestic students, international students had even worse experiences during the COV-ID-19 lockdown, as they were separated from their families, friends, and familiar surroundings due to the travel ban and border restrictions, and that this situation may have strained their coping mechanisms and living habits. The proportion of participants with high adherence to the MD varies widely between studies, even between those conducted in the same country: this is because different scales and thresholds were used, but probably also to the presence of selection biases. Data from a cross-sectional study representative of the Spanish general adult population conducted in 2008-2010 on 11,742 subjects reported 12% (95% CI: 11.3-12.7%) MD strict compliance, and 46% (95% CI: 44.7-47.7) moderate compliance (76) , and these results are very different from those obtained by Franco (34) , Tárraga Lopez (38) , and colleagues, included in our review.

Regarding cereal consumption, the results of the included studies are heterogeneous and conflicting, and no generalizable conclusions can be drawn. Dragun (39), Galali (41), Pfeifer (40) , Rodríguez-Pérez (36), Ruggiero (44) , Sánchez-Sánchez (37), Suelejmani (45) and their colleagues found an increase in the consumption of legumes, vegetables and fruit, while Giacalone et al. (42) found a decrease in the consumption of these food items. For each study reporting the percentage of participants who stated that they had increased or decreased their consumption of a certain food during the lockdown, we determined the overall percentage change, i.e. the difference between the percentage of participants who reported increasing their intake and the percentage of participants who reported decreasing their intake, and found that for legumes it ranged from -1.5% to +11.0%, for vegetables from -8.2% to +50.0%, and for fruit from -13.9% to +45.7%. Three (37, 41, 44) of the four studies that assessed nut consumption concluded that it had increased during the lockdown (the overall percentage change ranged from +4.9% to 17.6%), while one (39) found that it had dropped. Cooking time may have grown during confinement, resulting in higher consumption of healthy foods (34, 35) . The data is very heterogeneous and difficult to compare when it comes to meat consumption, so it is impossible to summarize the effect of lockdowns on consumption, which appears to vary greatly by geographical area. However, four studies (40, 42, 44, 45) reported a reduction in red meat intake, while three (37, 39, 41) studies found an increase. Two studies (41, 44) found that dairy consumption had increased during lockdowns compared to earlier periods, while one found that it had decreased (39) .

Data on egg consumption is limited because just two studies (39, 41) have analyzed it, but it appears to have increased in general. Five studies found an increase in olive oil use (36, 37, 40, 44, 45) , while one study found a modest decline (42) (the overall percentage change ranged from -0.2% to +13.0%). Data on fish consumption is also heterogeneous; nevertheless, six studies (37, 39, 41, 42, 44, 45) found that consumption increased during national lockdowns compared to previous periods, while two studies (36, 40) found that consumption decreased. Finally, three (36, 40, 42) out of four studies found an increase in all alcoholic beverage consumption, while one (45) found a decrease (the overall percentage change ranged from -39.0% to 46.9 ). An increase in alcohol consumption has indeed been reported by some authors and may have constituted a coping strategy in some populations (77) . Our results suggest a possible increase in adherence to DM in some settings and in the consumption of healthy foods during COVID-19-related national lockdown, but also a possible increase in consumption of unhealthy foods. The study "COVID-19 impact on consumer food behaviours in Europe", which was funded by the European Institute of Innovation & Technology (EIT) and involved 5000 consumers in 10 European countries, found that from the beginning of the COVID-19 outbreak to September 2020, the majority of people spent more time cooking and experimenting with new recipes (78) . Home cooking makes people have an active role in their dietary habits and could influence a healthy diet follow-up (79) . However, the stress and boredom associated with isolation may have increased emotional eating (36) , leading to a concomitant increase in comfort food consumption and unhealthy food in general; for example, an increase in the amount and frequency of snack consumption has been reported by eight (36, 37, 40, 41, (43) (44) (45) of the included studies. Another finding of our review is that the COVID-19 pandemic may have most adversely affected the most vulnerable groups in society (35, 36, 44, 80) who should be particularly supported in accessing safe and healthy food and understanding the importance of healthy dietary choices. Our study has both strengths and limitations. To the best of our knowledge, it is the first systematic review conducted to assess changes in adherence to the Mediterranean diet during COVID-19 related national-level stay-at-home orders; we included only studies using validated scales to assess MD adherence and we applied solid systematic revies' methodology. Nevertheless, some limitations should also be considered. Firstly, all observational studies could be prone to recall bias or social desirability bias affecting the certainty and quality of data collected. This is particularly true for cross-sectional studies that are also potentially affected by reverse causality. Moreover, included studies may be subject to selection bias, potentially affecting representativeness since all of the included studies used snowball sampling, except the study by Medrano et al.(35) , used snowball sampling. Finally, the studies' results were heterogeneous for several reasons: for example, different MD scores were used, with different score thresholds to define adherence to MD, and different study populations were considered. The results of our systematic review provide useful insights into the implications of restrictive measures, particularly national lockdowns, on dietary habits and contribute to public health policy decision-making. Further research will be useful to better identify the determinants of adherence to MD and which strategies can be adopted to sensitize people to adopt healthy lifestyles.

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Central obesity and the Mediterranean diet: A systematic review of intervention trials

The Effect of Mediterranean Diet on Metabolic Syndrome and its Components

How western diet and lifestyle drive the pandemic of obesity and civilization diseases. Diabetes, Metab Syndr Obes Targets Ther

Long-term effects of western diet consumption in male and female mice

Dose-response relationship between western diet and being overweight among teachers in Malaysia

A Western dietary pattern is prospectively associated with cardio-metabolic traits and incidence of the metabolic syndrome

Dietary patterns and risk for type 2 diabetes mellitus in U.S. men

Metabolically healthy obese and metabolic syndrome of the lean: The importance of diet quality. Analysis of MAGNETIC cohort

Diet and physical activity during the coronavirus disease 2019 (COVID-19) lockdown

Changes in diet quality and food security among adults during the COVID-19-related early lockdown: Results from NutriQuébec

Changes in consumers' food practices during the covid-19 lockdown, implications for diet quality and the food system: A cross-continental comparison

Changes in dietary patterns among youths in China during COVID-19 epidemic: The COV-ID-19 impact on lifestyle change survey (COINLICS)

The Lancet Gastroenterology & Hepatology. Obesity: another ongoing pandemic

Obesity pandemic: causes, consequences, and solutions-but do we have the will?

Arteriosclerosis, Thrombosis, and Vascular Biology

Overview of the metabolic syndrome; an emerging pandemic of public health significance

Global pandemics interconnected -obesity, impaired metabolic health and COVID-19

Weight perception among Italian adults

Overweight and obesity prevalence and determinants in Italy: An update to 2010

Eating in the lockdown during the Covid 19 pandemic; self-reported changes in eating behaviour, and associations with BMI, eating style, coping and health anxiety

COVID-19-Related Quarantine Effect on Dietary Habits in a Northern Italian Rural Population: Data from the Brisighella Heart Study

Susceptibility to increased high energy dense sweet and savoury food intake in response to the COVID-19 lockdown: The role of craving control and acceptance coping strategies

Food insecurity and its association with changes in nutritional habits among adults during the COVID-19 confinement measures in Belgium. Public Health Nutr

Mediterranean diet assessment challenges: Validation of the Croatian Version of the 14-item Mediterranean Diet Serving Score (MDSS) Questionnaire

Adherence to the Mediterranean Diet Pattern Has Declined in Spanish Adults 1-3

Changes in Alcohol Use During the COVID-19 Pandemic: Impact of the Lockdown Conditions and Mental Health Factors

COVID-19 impact on consumer food behaviours in Europe

Covid-19 confinement and changes of adolescent's dietary trends in Italy

The impact of the current economic crisis on mental health in Italy: Evidence from two representative national surveys

Records marked as ineligible by automation tools (n = 0) χ Records removed for other reasons (n = 0) †Records removed by automation tools (n = 23+1) Records removed by authors (n = 6) Total identified studies after duplicate removal (n = 27)

Records screened (n = 27) Reports sought for retrieval (n = 17) Reports assessed for eligibility (n = 17) Studies included in review (n = 12)