Educational Interventions for Promoting Food Literacy and Patient Engagement in Preventing Complications of Type 2 Diabetes: A Systematic Review

The present review aims to map the current literature on educational interventions to promote food literacy in type 2 diabetes, with a particular focus on the concept of patient engagement. The systematic review was implemented on five databases with no restrictions on the publication year. The studies selected for the review were focused on patients with type 2 diabetes, ranging from 2003 to 2021 and published in 13 countries (44% USA). Thirty-three articles were analyzed. Twenty-seven articles targeted singular patients; fifteen articles conceptualized patient engagement as self-management. In seven articles, the provider is a multidisciplinary team. Twenty articles did not report a theoretical framework in the intervention development, and eleven did not use an intervention material. Twenty-six articles did not use a technology proxy. Outcome categories were narratively mapped into four areas: clinical, psychological, behavioral, and literacy. To date, most of the interventions are heterogeneous in the adopted methodology, measures, and outcomes considered. More attention should be given to the psychosocial characterization of patient engagement as well as the technological support. High-quality, randomized controlled trials and longitudinal studies are lacking and need to be conducted to verify the efficacy of these insights.


Introduction
Diabetes is a major public health concern that is approaching epidemic proportions globally [1]. About 422 million people worldwide have diabetes, and 1.6 million deaths are directly attributed to diabetes each year. The most common is the type 2 diabetes. In the past three decades, the prevalence of type 2 diabetes has risen dramatically in countries of all income levels [2].
There is substantial evidence that leading a healthy lifestyle, including following a healthy diet, achieving modest weight loss, and performing regular physical activity, can maintain healthy blood glucose levels and reduce the risk of complications of type 2 diabetes [3]. Indeed, the American Diabetes Association (ADA) published guidelines highlighting that self-management and education are crucial aspects of diabetes care allowing the optimization of metabolic control, the improvement of overall quality of life, and the prevention of acute and chronic complications [4]. Given its nature, primary care can be a valuable setting for preventing diabetes and its complications in at-risk populations because it is a patient's primary point of contact with the health care system. Patients can be offered support by primary care health professionals (e.g., general practitioners, practice nurses) for prevention, such as screening and lifestyle advice, as well as monitoring health outcomes [5]. For these reasons, scholars have been studying how to educate and engage patients in effective behavioral change towards better health outcomes [6][7][8]. The concept of food literacy is recognized in the literature as a fundamental ingredient for the management of chronic diseases, such as type 2 diabetes [9]. This concept is defined in the literature as the ability to develop knowledge and skills in food management, and it is a multi-componential concept that includes several aspects [10]. In a recent review of the literature [11], authors systematized the various definitions of food literacy, identifying these constitutional components: food skills, food nutritional knowledge, self-efficacy and attitudes towards food, food and dietary behaviors, ecological factors (socio-cultural, influences, and eating practices). This multi-component nature was also highlighted in the review from 2017 by Truman and colleagues [12]. However, both scholars and institutions suggested that knowledge alone is not sufficient to sustain a behavioral change in disease management, but it is necessary to gain a broader perspective that considers patients' psychosocial aspects and how they contribute to their engagement in the care [13][14][15][16]. Recently, the World Health Organization confirmed the support of a change in this direction with the Shanghai 2016 declaration [17] that promotes both health literacy and empowerment for individuals to enable their participation in managing their health. Over the past 50 years, an extensive body of literature has emerged describing several concepts of the relationship between patients and healthcare systems. In this perspective, the patients are considered as full members of the healthcare team [18] not only with their disease but also with their psychological uniqueness, values, and experience [12,19,20] as the human component of the care. For the patients, to assume an active role in disease management, it means to shift from being a passive user of the healthcare services to being an active partner, emotionally resilient, and behaviorally able to adjust medical advices to their own disease status [16,21,22]. In fact, people with high levels of engagement have been identified as more effective in enhancing behavioral change and in adhering to medical prescriptions [23,24] and in diabetes management [25] and in having an overall better quality of care.
To sum up, in the past decades, the shift towards a more multifaceted approach to patients with diabetes is challenging the public health sector to lever on the patients themselves as the key actors for implementing effective educational interventions. In this scenario, concepts related to patient engagement have been recognized as an essential topic to sustain type 2 diabetes disease-management and prevention behaviors. However, the relative newness of this concept and the fragmentation of articles applying it to food literacy educational interventions in the scientific debate urges for a systematization aimed at providing innovative insights.
In line with these premises, the aim of this systematic review is to map educational intervention for patients with type 2 diabetes in order to promote food literacy, with a particular focus on patient engagement, and to discuss the results about disease complications' prevention.

Materials and Methods
The systematic review protocol was registered in 2020 in the international prospective register of systematic reviews. The registration number is CRD42020167938.

Literature Search Strategy
A Boolean search string was created using the elements of the PICO model (P, population/patient; I, intervention/indicator; C, comparator/control; and O, outcome) to search for relevant articles in the MEDLINE, Cochrane Library, Web of Science, EMBASE, and Scopus databases [26]. References of individual studies were also back-checked. Articles were retrieved from the inception of each database until April 2021.
This systematic review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines for the reporting of systematic reviews [27].

Inclusion Criteria
The inclusion of relevant studies was based on the following criteria: (1) researches explicitly involving adult patients with type 2 diabetes as a unique or secondary condition as the main target of the intervention; (2) studies describing educational interventions (intended as standardized protocols, programs, courses implemented face-to-face or online, with or without the direct presence of a healthcare professional, and/or delivered with the support of dedicated educational materials); (3) studies analyzing educational interventions explicitly addressing food literacy, nutritional literacy, and/or health literacy; (4) studies reporting a measured outcome (measured with direct or self-reported tools) describing a psychological and/or motivational improvement of the patients (potentially labeled as patient empowerment, self-management, patient involvement, adherence, and compliance; patients activation; quality of life) [28]; and (5) studies involving individual, dyadic, and/or group interventions either self-administrated or administered by a healthcare professional. We focused on primary studies reporting efficacy results. The inclusion was restricted by age of participants (i.e., >18 year old), English language only, and availability of full texts published in peer-reviewed journals.
After removing duplicate results, four researchers (S.M., A.G.M., N.M.C., S.M.) independently screened the title and abstract to outline the most appropriate articles. Then, the four researchers performed a full-text screening of each article to determine eligibility. First, the four researchers screened a pull of 20 articles together, with the aim to fine-tune the screening process and solve eventual misalignments. Secondly, the four researchers independently read the abstracts and proceeded with the selection of the pertinent ones. During the screening process, the researchers solved any ambiguous situation or bias by discussing together the inclusion or exclusion of the article based on the eligibility criteria identified and their expertise on the topic.
The following PRISMA flow diagram reports the systematic review's search and selection process of studies for inclusion ( Figure 1).

Data Extraction and Quality Assessment
Data extraction was independently completed by four researchers (MS, GA, MCN, MS), adopting a standard data-entry electronic form. Data on study characteristics (i.e., author name, country or region of study, year of publication, study design), participantsrelated aspects (i.e., sample size, sex, age), intervention-related aspects (i.e., target and provider of intervention, duration of intervention, type and description of intervention, technology proxies, theoretical frameworks, conceptualization of patient engagement provided), and outcome-related aspects (i.e., outcome category and timing, outcome measurement tools) were extracted from each included study.
Study quality was measured using the Quality Criteria Checklist for primary research provided by the American Diabetes Association, assigning each study a rating of negative, neutral, or positive [29]. This checklist includes ten validity questions based on the Agency for Healthcare Research and Quality (AHRQ) domains for research studies. Sub-questions are listed under each validity question that identifies important aspects of sound study design and execution relevant to each domain. Some sub-questions also identify how the domain applies in specific research designs. Additionally, as established by the checklist guidelines, to address the heterogeneity of study designs, the several sub-

Data Extraction and Quality Assessment
Data extraction was independently completed by four researchers (MS, GA, MCN, MS), adopting a standard data-entry electronic form. Data on study characteristics (i.e., author name, country or region of study, year of publication, study design), participantsrelated aspects (i.e., sample size, sex, age), intervention-related aspects (i.e., target and provider of intervention, duration of intervention, type and description of intervention, technology proxies, theoretical frameworks, conceptualization of patient engagement provided), and outcome-related aspects (i.e., outcome category and timing, outcome measurement tools) were extracted from each included study.
Study quality was measured using the Quality Criteria Checklist for primary research provided by the American Diabetes Association, assigning each study a rating of negative, neutral, or positive [29]. This checklist includes ten validity questions based on the Agency for Healthcare Research and Quality (AHRQ) domains for research studies. Sub-questions are listed under each validity question that identifies important aspects of sound study design and execution relevant to each domain. Some sub-questions also identify how the domain applies in specific research designs. Additionally, as established by the checklist guidelines, to address the heterogeneity of study designs, the several sub-questions were adapted to the specific study design of each eligible article. Moreover, to obtain a summary score for each validity question, a threshold was identified. In particular, if the answers to the sub-questions of each domain were "yes" in more than 50% of them, then the summary score was "yes"; if the answers to the sub-questions of each domain were "no" or "unclear" in 50% or more of them, then the summary score was "no". Moreover, on the basis of the American Diabetes Association guidelines, the score was rated taking into account that, among the signaling questions, the numbers 2, 3, 6, and 7 (i.e., Was the selection of study subjects/patients free from bias?; Were study groups comparable?; Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described?; Were outcomes clearly defined and the measurements valid and reliable?) were deemed to be of higher importance with respect to the others.

Data Synthesis and Analysis
The main features of the articles were extracted and described. Patient engagement was described in terms of the different conceptualizations and relative theoretical framework used. The level of food literacy and patient engagement were also analyzed since the expected significant variability in relation to different educational interventions. Results were analyzed and summarized narratively considering the methodological quality and scope of each study.
Moreover, other studies described by this review considered aim of the intervention; intervention target; intervention provider; theory explicated; technology proxy involved; intervention materials; and outcome measure. Table 2 provides an overall risk score for the included studies. The majority of the studies (n = 25) were identified as neutral in rating quality.

Quality Assessment
Y, yes; N, no; NA, not applicable; U, unclear; +: the report has clearly addressed issues of inclusion/exclusion, bias, generalizability, and data collection and analysis.
Twenty-one studies were rated negatively in the intervention/exposure validity question (i.e., Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described?). The vast majority of articles (n = 27) did not use blinding to prevent introduction of bias (i.e., Was blinding used to prevent introduction of bias?), while 27 studies did not describe methods of handling withdrawals (i.e., Was the method of handling withdrawals described?).
All the included articles conducted the most proper statistical analyses, while the majority (n = 28) of studies supported their conclusions taking into consideration biases and limitations.
Was the research question clearly stated? 2.
Was the selection of study subjects/patients free from bias? 3.
Was method of handling withdrawals described? 5.
Was blinding used to prevent introduction of bias? 6.
Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described? 7.
Were outcomes clearly defined and the measurements valid and reliable? 8.
Was the statistical analysis appropriate for the study design and type of outcome indicators? 9.
Are conclusions supported by results with biases and limitations taken into consideration? 10. Is bias due to study's funding or sponsorship unlikely?

Patient Engagement Components
We classified the articles on the basis of the way patient engagement (as intended in this review) was conceptualized in the studies. In greater detail, fifteen articles conceptualized it as self-management alone [32,33,36,42,52,53] or together with other variables, such as quality of life, patient participation, or self-efficacy [6,8,35,38,40,44,47,48,51]. Seven articles described some kind of participation of the patients or the families into the definition or the adjustment of the intervention [30,31,34,37,41,46,54] in order to consider their opinion and to better target the intervention itself. Three articles included an evaluation of patient adherence to the treatment or the prescriptions [45,50,56] together with broader quality-oflife or empowerment measures. Three included the concept of patient activation [43,49,50]. Three included quality-of-life measures [55,58,59]. One used patient engagement [39] and one patient empowerment [7].

Intervention Provider
Eight articles described the intervention provided by a multidisciplinary team [31,34,44,48,51,55,57,58] among the others, composed by endocrinologists, general practitioners, ophthalmologist, podiatrist nutritionists, nurses, educators, physical therapist or rehabilitation specialist, dietitian, psychologist, dermatologist, and dentist. Five articles were by a nurse, of which two were practicing alone [33,37], one under the supervision of a specialist [39], and two by a nurse specialized in diabetes education [36,49]. In five articles, the researchers provided the intervention itself [7,43,46,47,59]. Four articles were by lay workers [38,41,52,53]. Three articles were by educators [6,40], in one case alternatively to a health professional [6]. In three articles, the intervention was delivered by a pharmacist [35,54,56], and in the other three, the provider was not specified [8,32,45]. Finally, one article described the intervention as provided by a doctor [30] and one article by a coach [50].

Theoretical Framework
Seventeen articles did not report a theoretical framework as the base for intervention development [31,33,35,37,39,42,43,47,50,[52][53][54][55][56][57][58][59]. The other articles explained the theoretical framework or theory behind intervention development (n = 15). In particular, two articles reported the Social Cognitive theory inspired by Bandura [40,49,60]; one cited the Health-Belief Model [45,61]; and one the Trento Model by Trento and colleagues (2005) [51,62]; one article explicated theory related to self-efficacy in association with the Social Support Theory by Vaux (1998) [30,63] and two related to the concept of empowerment [41,59]; and one referred to the problem-solving model of chronic disease self-management by D'Zurilla and Nezu (1990) [32,64]. Finally, six articles framed the intervention in a more complex framework for behavioral change. Two of them referred to the PRECEDE model (Predisposing, Reinforcing, and Enabling Constructs in Education/Environmental Diagnosis and Evaluation [38,46] inspired by Lusk et al. [65]; one to the Information-Motivation-Behavioral Skills (IMB) [34,66]; one to the diabetes outpatient intensive management program (DOIMP) [48]; one to the causal pathway proposed by Fransen and colleagues (2012) [67]; and one to the Diabetes Self-Management Outcome Framework (DSMOF) [6]; and one article included a toolkit based on two previous validated models: the Diabetes Literacy and Numeracy Educational Toolkit and The American College of Physicians Foundation Living With Diabetes Guide [44]. We also crossed the theoretical framework with the conceptualization of patient engagement proposed by the different authors ( Figure 2).

Theoretical Framework
Seventeen articles did not report a theoretical framework as the base for intervention development [31,33,35,37,39,42,43,47,50,[52][53][54][55][56][57][58][59]. The other articles explained the theoretical framework or theory behind intervention development (n = 15). In particular, two articles reported the Social Cognitive theory inspired by Bandura [40,49,60]; one cited the Health-Belief Model [45,61]; and one the Trento Model by Trento and colleagues (2005) [51,62]; one article explicated theory related to self-efficacy in association with the Social Support Theory by Vaux (1998) [30,63] and two related to the concept of empowerment [41,59]; and one referred to the problem-solving model of chronic disease self-management by D'Zurilla and Nezu (1990) [32,64]. Finally, six articles framed the intervention in a more complex framework for behavioral change. Two of them referred to the PRECEDE model (Predisposing, Reinforcing, and Enabling Constructs in Education/Environmental Diagnosis and Evaluation [38,46] inspired by Lusk et al. [65]; one to the Information-Motivation-Behavioral Skills (IMB) [34,66]; one to the diabetes outpatient intensive management program (DOIMP) [48]; one to the causal pathway proposed by Fransen and colleagues (2012) [67]; and one to the Diabetes Self-Management Outcome Framework (DSMOF) [6]; and one article included a toolkit based on two previous validated models: the Diabetes Literacy and Numeracy Educational Toolkit and The American College of Physicians Foundation Living With Diabetes Guide [44]. We also crossed the theoretical framework with the conceptualization of patient engagement proposed by the different authors ( Figure 2).

Outcome Measure
The outcome measures were classified based on the outcome category. Clinical measurements often occurred with standard techniques, so the measure tool was unspecified in most cases. A summary of the outcome categories and related measure tools are reported in Table 3.

Discussion
The present systematic review mapped the educational interventions for type 2 diabetes patients aimed to promote food literacy, with a specific focus on patient engagement conceptualizations. All the interventions described in the included articles have highlighted how taking actions aimed at improving food literacy is a key element in achieving diabetes management [9].
Since patient education in type 2 diabetes is becoming more multifaceted and trying to integrate psychosocial aspects and literacy, scholars have published an increasing number of articles to investigate the effects of these variables on patients' outcomes. This systematic review offers an integrated view on the phenomenon that categorizes the main features of the interventions and assesses the quality of the studies published to date. In greater detail, the articles included in this review ranged from 2003 to date, suggesting that scholars started to consider both aspects of food literacy and patient engagement only in the last two decades. The care of chronic diseases requires a deep reconfiguration of the patients' life and the adaptation to a new lifestyle, which also encompasses disease management. For this reason, a more integrated approach to the education of these patients could have positive effects on both clinical [40,48,50] and psychosocial outcomes [46,55]. This appears to be in line with the conceptualization of patient-centered care proposed at the beginning of the new millennium [68]. This is also particularly relevant in the field of chronic diseases [69], such as diabetes. Overall, as highlighted in the latest literature [70], signals suggesting the increasing willingness of scholars to broaden the idea of diabetes education by approaching it from a multifaceted perspective were found. In our review, most of the articles conceptualized patient engagement in terms of self-management. Fewer studies included the idea of patients' active participation in the development or fine-tuning of the intervention or to involve them in the decision making along the care journey. Even if these results could be interpreted as a first step towards the inclusion of patients as an active part of the care team, this idea is still conceptualized and limited to care management [36,47]. In line with this consideration, the theoretical frameworks mapped here also belong mainly to the self-management area. Patients' ability to manage their care with awareness and specific skills is surely recognized as one of the primary goals of the care process [47]. However, recently, scholars called for a more integrated approach to patients in which they should be considered as a member of the team itself, with their behavioral and psychological resources [69]. The same emerged for the concept of food literacy, which was measured in the articles analyzed here as following more an operational definition rather than a multifactorial and social one. This appears to be in contrast with the recent literature that claims the need to overcome a vision of food literacy only aimed at filling patients' knowledge gaps with information [71]. It now appears urgent to frame food literacy in a more subject-centered approach to literacy.
Our systematic review also highlights a relevant involvement of the multidisciplinary team in the education interventions [38,51,55,58]. In line with the premises of this review, this result suggests that in the last years, the education of patients with type 2 diabetes involves different specialists able to work together to guarantee positive outcomes, as described by different authors from our work [51,58]. These results appear encouraging if framed in the recent literature that highlights how the support of different health professionals could be beneficial for the patients [72] and for the care team [73][74][75]. This is in accordance with the quadruple aim, which fosters both the enhancement of patients' experience and the care-team wellbeing [76].
Our review further mapped that most of the studies adopted tools that were developed for the specific investigation being reported and did not use a validated theoretical framework [33,47,77]. The lack of theory-driven intervention could be discussed considering the difficulty to adapt specific educational objectives, which depends largely on the patients' characteristics, such as literacy level, as discovered by Kim and colleagues (2019) [49], who found effective results in patients with lower initial literacy. However, the risk of not using a theory-driven intervention is that the results may remain fragmented without the possibility to guide other future research.
Our systematic review also mapped the use of a technology proxy, which is nowadays recognized as an efficient support in boosting patients' education, as already established by a previous research underlying that technological interventions could benefit people living with diabetes [78]. Only a few articles included a web tool (e.g., social media, web sites, apps) in their educational intervention [30,33,39]. However, it can be discussed, as the use of the Internet is relevant and also in the light of the recent COVID-19 pandemic, which called for the reconfiguration of the healthcare system in hybrid online-offline forms [79]. The use of telemedicine, for example, is described as an ally able to guarantee continuity of care and quality of life to patients [80]. For this reason, the use of technology to engage patients in the educational interventions should be encouraged in order to overcome possible barriers.
With regards to the quality of included studies, a consideration should be done when interpreting the findings. It should be acknowledged that in the QCC quality assessment checklist, the validity question concerning the full description of the adopted intervention and comparison (i.e., Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were intervening factors described?) has a significant weight on the assessment of the included studies since most of them were rated negatively in this domain.
To conclude, given the mutated health needs of diabetic patients, the increasing burden of chronic disease on health systems, and the necessity of proper communication flows with respect to the past years, the present findings suggest that the research is struggling to bridge this gap in type 2 diabetes management. Food literacy and patient engagement should be considered as strongly related to patients' care and should be assessed with validated measures in order to fine-tune the intervention and obtain more efficient results. In addition, the conceptualization of patient engagement should turn to considering a broader involvement of the patients not only in terms of self-management but also increasing their psychological engagement in all the care process. In doing so, disease management should be considered as a real lifestyle change, and in these terms, it demands that the patients not only to be instructed with information but also with appropriate tools that allow them to become an active partner of the care process. With this aim, web tools could be an enabler to facilitate this process by guaranteeing continuity of care and to actively involve patients but also to enhance professional exchange, which is relevant in chronic disease management.
The present systematic review has strengths and limitations. It was conducted according to widely used methodological frameworks, such as PRISMA guidelines for the collection analysis and the QCC-validated quality checklist, which guaranteed the rigor of the results. However, due to the heterogeneity of the adopted measurement tools and variables, it was not possible to conduct a meta-analysis. Additionally, we included a broad range of studies, which may limit the review's design. Nevertheless, wider inclusion of studies is needed since, sometimes, RCT is not the most suitable design for literacy and engagement interventions.
In addition, differently from other recent reviews on the same population focusing particularly on one outcome (e.g., glycemic control) [81], the present systematic review took into account several outcomes. Although it was impossible to evaluate the efficacy of the individual studies' features on the outcome assessment (e.g., glycated hemoglobin), in our review, we proposed a taxonomy of the main conceptualization of patient engagement with relative theoretical frameworks, which can be used to guide health policies for public health practitioners and decision makers. To do so, future studies are encouraged to use validated tools to measure both literacy and engagement in order to allow other researchers to compare the effectiveness of the results. Further studies investigating whether the several definitions of food literacy align with more nuanced understandings of food literacy, as reported in the scientific literature [82], are needed. Moreover, future researches providing a structured understanding of food literacy are imperatively required.
Besides, additional researches adopting technologies and, consequently, assessing their effects on outcomes are essential since, to date, it has been proven to result in relative utility and efficacy in patients' education.

Conclusions
In the current systematic review, we reviewed and synthesized the literature on interventions for food literacy and patient engagement targeting patients with type 2 diabetes. The review identified that, to date, interventions are heterogeneous in the adopted methodology, measures, and outcomes considered. The majority of the scientific debate focused both on literacy and engagement aspects, the latest mainly conceptualized as self-management. The majority of the studies involved a multidisciplinary team. Indeed, addressing food literacy in multidisciplinary diabetes educational and management programs improves important health outcomes. In addition, we found that the support materials used the most are paper-based or video; however, even if considered less to date, technology tools (e.g., social media, web sites, and apps) should be encouraged to stay in touch with the patients and to enhance their involvement in the educational intervention. The results presented in the review suggested some recommendations and practical implications based on the synthesis of current scientific debate. However, high-quality, randomized controlled trials and longitudinal studies are lacking and need to be conducted to verify the efficacy of these insights.