Dietary Interventions to Promote Healthy Eating among Office Workers: A Literature Review

Our aim is to review published studies on dietary interventions to promote healthy eating habits among office workers. The databases PubMed, EBSCO (MEDLINE, Academic Search Elite, CINAHL Plus, PsycARTICLES, PsycINFO), Cochrane Library, SCOPUS, and Google Scholar were searched between February and April 2019. Initially, 6647 articles were identified, and the final number of articles that met the inclusion criteria was 25. We identified four different types of interventions that included educational and/or environmental components, where environmental components provided healthy food in a work-related context. The interventions at the offices included web-based material, availability of food, provision of information in various ways, and a combination of environmental, educational and theory-based psychological approaches (i.e., multicomponent). The most commonly used designs were web-based and information interventions, respectively, which are the least expensive ways to intervene. The interventions assessed a range of outcomes, but this literature review focused on three, i.e., dietary intake, dietary behavior and health-related outcomes. Although the studies were heterogenous in terms of outcomes, design, number of participants, gender distribution and duration, all studies reported at least one positive effect. Thus, workplace dietary interventions are an unutilized area to positively influence dietary intake and health outcomes among office workers. However, the intervention needs to be tailored to the workplace.


Introduction
Non-communicable diseases (NCDs) such as obesity, cardiovascular diseases (hypertension, stroke, and atherosclerosis), various types of cancer (breast, colon, and prostate), and type II diabetes are the leading cause of death globally, and one of the major health challenges of the 21st century [1]. Every day, 3.45 billion people go to work [2] and NCDs contribute 70%, injuries 22% and infectious diseases 8% to the total disease burden from occupational risks [3].
More than half of the employees in Sweden work in offices, [4] and the situation is the same in many other developed countries (e.g., Germany) [5]. Working in an office setting is characterized by sedentary work, and the main components associated with the development of NCDs are physical inactivity and poor food habits [6]. An office worker is defined as "an employee who works in an office, especially one engaged in clerical or administrative work" [7]. Another term for this type of work is white-collar workers and they are defined as "people who work in offices, doing work that needs mental rather than physical effort" [8]. Coincidently, the retirement age has increased, and people need to work for more years and at older ages, including an age where age-related NCDs are getting more common. The general retirement age in the EU Member States is 65 years. Germany, Spain and France are about to raise their retirement age from 65 to 67 years, while, in Ireland and Britain, the aim is 68 years. Furthermore, due to the increase in life expectancy, the retirement age in many countries such as Cyprus, Estonia, Denmark, Italy, Greece, Portugal, the Netherlands and Slovakia will increase as well between 2020 and 2030 [9]. Thus, it is crucial that precautionary actions are taken to prevent the development of NCDs and to help manage early stages of NCDs by offering healthy lifestyles at work.
The workplace is and can be one of the most important settings affecting eating habits and the physical, mental and social well-being of office workers. A substantial proportion of the adult population spends a significant amount of time at work each day and a large number of individuals can be targeted simultaneously in a work office-based intervention. Moreover, these types of interventions may be advantageous because they are convenient and easily accessible to workers and allow employees to interact and support each other in their efforts to undertake behavior changes [10]. Full-time employees spend up to 60% of their waking hours at work [11] and typically return repeatedly to the same location, providing a significant opportunity to deliver health interventions to a target population. Thus, office-based wellness programs may be an ideal large-scale strategy to promote healthy behaviors to combat this rise in NCDs. Moreover, the health care system and employers may benefit from reduced incidence of NCDs among office workers since a considerable amount of tax money is spent on treating chronic diseases and companies are suffering from productivity losses [12].
To the best of our knowledge, this is the first literature review comprising published studies worldwide focusing on either dietary or multicomponent lifestyle interventions among office workers. Here, we present the effects on diet, dietary behavior and health-related outcomes for various types of interventions, and the results may be implemented in office contexts.

Methods
This literature review aims to investigate and describe the published up-to-date data on the effectiveness of dietary interventions for promoting healthy eating habits and healthy lifestyles among office workers.

Inclusion Criteria
The following criteria were applied in the literature search of published research articles: the articles had to (1) be published between 1999 and 2019; (2) be published in the English language; (3) be interventions in an office setting; (4) explicitly describe dietary intervention components or the impact of a multicomponent intervention on diet-related outcomes (changes in dietary intake); (5) describe the effect of dietary intervention components on dietary behavior-related outcomes (i.e., knowledge, attitude and skills related to dietary intake) and health-related outcomes (i.e., weight, BMI, waist circumference, blood pressure, blood lipids, fasting blood glucose); (6) include healthy office workers as well as office workers with overweight, metabolic syndrome and potentially other health problems; and (7), for studies with environmental intervention, the intervention must have been conducted within a workplace, or frequented by office employees for eating.
No limitations were set as to the subject characteristics (e.g., gender), worksite size (e.g., number of employees), follow-up measurements (e.g., short-term, long-term), control group (e.g., health risks appraisal (HRA), waiting list, and no intervention), type of intervention (e.g., environmental, educational, and multicomponent) or study design. We included intervention studies with different designs, including randomized controlled trials and before-after designs at a single site, in order to capture as many relevant studies as possible to study the effectiveness of dietary interventions in an office setting. Studies without an intervention component (e.g., observational) and non-dietary interventions (e.g., exercise) were excluded.

Data Sources/Literature Search
Articles were identified by searching five electronic databases and reviewing reference lists of articles, relevant review articles, recommended articles, and meta-analysis. Recommended articles were retrieved from the option "similar articles" in PubMed. This search was applied to PubMed, EBSCO (MEDLINE, Academic Search Elite, CINAHL Plus, PsycARTICLES, PsycINFO) Cochrane Library, SCOPUS, and Google Scholar. A time restriction was applied for articles published between 1 January 1999 and 15 April 2019, and the final search was done on 16 April 2019.
The following keywords were used in various combinations to search all databases: "office worker*" OR "office employees*" OR "white collar*" OR "sedentary occupation" OR "sedentary job" AND "healthy eating" OR "healthy diet" OR "healthy nutrition" OR "healthy eating behavior" AND intervention* OR program* AND "worksite health promotion" OR "workplace health promotion".
Due to the small number of identified articles when using the keywords, the majority of articles were found via the feature recommended articles in PubMed and by screening the reference lists of all previously identified articles using a snowballing approach.

Search Outcome
The search in five databases, the recommended articles in PubMed and the reference lists provided a total of 6647 articles. From the initial review, 5598 articles were discarded after screening titles. Eight hundred fifty-one articles of the remaining 1049 were removed after a review of abstracts since they did not meet the inclusion criteria, i.e., it was not clear from the abstract if they included office workers and/or a dietary intervention. A total of 198 full-text articles were assessed for eligibility and 95 remained after adjusting for duplicates.
The full text of the remaining 95 articles was read in more detail and 70 studies did not meet the inclusion criteria. These articles were rejected for several reasons, for example, some studies included a combination of white-and blue-collar workers, some studies were not intervention studies and some did not have diet as the main focus. A total of 25 articles from 17 unique trials were identified for inclusion in the present review; see the selection process in Figure 1. Four of these final articles were identified in the database screening with keywords and 21 articles were identified by checking the reference lists and relevant articles in PubMed. No unpublished studies were obtained.

Study Selection
Two reviewers (AC and AG) independently applied the inclusion criteria to select potentially relevant articles from the titles, abstracts and keywords of the references retrieved from the literature search and the reference lists of articles, relevant review articles, recommended articles, and meta-analysis. Disagreements between reviewers were resolved by consensus. The inclusion criteria were pilot tested by both reviewers on one article that was not included in this review, to resolve the initial disagreement.

Study Selection
Two reviewers (AC and AG) independently applied the inclusion criteria to select potentially relevant articles from the titles, abstracts and keywords of the references retrieved from the literature search and the reference lists of articles, relevant review articles, recommended articles, and meta-analysis. Disagreements between reviewers were resolved by consensus. The inclusion criteria were pilot tested by both reviewers on one article that was not included in this review, to resolve the initial disagreement.

Data Extraction/Data Collection Process
Data were independently extracted by the two reviewers using a data extraction form developed by us. Each study was summarized regarding the author and the year, the study design, follow-up duration, sample size, intervention type, intervention, incentive, outcome measures, and results, and listed in Tables 1-4. These tables focus on positive findings from the interventions, since the aim of the review paper is to highlight the potential of office based dietary interventions and not to compare studies. The data extraction form was pilot-tested on two articles. Disagreements were resolved by discussion between the two review authors.   Personal Nutrition Planner (PNP), an online nutrition intervention tool, which calculate participants' BMI, estimate energy expenditure and provide them with nutrition information IG: They registered on the site, completed the PNP and indicated if they wanted to receive weekly e-mail reminders (goals, steps and additional information). CG: They completed all the assessments like the IG. They were not provided with any health-related information, but they would receive access to the PNP after the study was completed. SCT 1.Dietary intake frequencies 2. Weight loss 3. Opinions regarding intervention IG vs. CG: IG performed significantly better than CG Dietary intake: Increase in weekly dairy intake from nearly 9 times per week (pretest) to nearly 11 times (2 months posttest) (p < 0.05) Weight loss: Among participants who wanted to lose weight, weight loss in the IG was significantly higher than that of the CG. (p < 0.05) Opinions regarding the PNP intervention: On a scale of 1-5, mean ratings of the PNP program characteristics ranged from 3-4.  Diet: Intake of nuts, fruits and seeds was significantly -increased by 34,9 g/day (p = 0.022) in the IG -decreased by 23.2 g/day (p = 0.022) in the CG Intake of dairy products was significantly -decreased by 4.1 g/day (p = 0.033) in the IG -increased by 42. The Internet-based program ExecuPrev™, trained managers to modify attitudes and behaviors, and built motivation to be healthy and effective leaders. IG: Health education (on diet, exercise, and stress) and leadership development exercises to enhance perceived career benefit of participating (lessons, webinars, additional links and interactive multi-media lessons).
CG    The results grew more pronounced as intake of Japanese-style healthy lunches increased in frequency Within CG: between baseline and follow-up Dietary intake: The "other vegetable" intake significantly decreased (240.1 g ± 128.5 g vs. 96.4 g ± 64.7 g, p = 0.015). Blood parameters: Hemoglobin A1c (HbA1C) levels had significantly increased (4.99% ± 0.29% versus 5.13% ± 0.21%, p < 0.05) Anthropometric data: No significant differences found on the perceived social support from colleagues regarding eating less fat in the IG, but at 12 months the attitude and self-efficacy towards eating less fat became less positive.
Self-efficacy towards eating less fat at work decreased significantly in the IG. This effect was also found at 12 months.  cholesterol, LDL and LDL/HDL ratio. Within IG: between baseline and follow-up EG: Aerobic power increased from 37.0 to 40.5 mL min −1 kg −1 (p < 0.01) DG: HDL increased from 1.12 to 1.27 mmol L −1 (p < 0.01), Tr decreased from 2.10 to 1.50 mmol l -1 (p < 0.05) and LDL/HDL ratio decreased from 3.86 to 3.32 (p < 0.05). SG: HDL increased from 1.10 to 1.23 mmol L −1 (p < 0.01), LDL/HDL ratio decreased from 3.43 to 2.97 (p < 0.05), DBP increased from 75 to 78 mmHg (p < 0.05) and aerobic power increased from 2.96 to 3.07 L min −1 (p < 0.05).  People could obtain the self-help manual for free by filling out a coupon that was included in the brochures.
1. Sales data: low-fat milk, butter, meat, cheese products and desert 2. Food intake LP vs. EP: Sales data: In the LP sales of low-fat desserts were increased (p < 0.01) LP vs. NP: Sales data: In the LP sales of low-fat desserts were increased (p < 0.05) Food intake: Total fat intake was decreased for respondents who believed they ate a high-fat diet (p = 0.04). Dietary intake: Fruits: Fruit consumption significantly increased at work (p = 0.04) A vs. B: fruit consumption in Group B was greater than that in Group A B vs. C: fruit consumption in Group B was greater than that in Group C It was more successful among those who were not meeting the recommendations (2 weeks post-intervention the change was not maintained p = 0.76) High fat snacks A vs. C: Group A decreased the number of high fat snacks consumed pre-to post-intervention and Group C increased high fat snack consumption B vs. C: Group B decreased the number of high fat snacks consumed pre-to post-intervention and Group C increased high fat snack consumption. Fat consumption was decreased to a greater extent in those who were not already eating two serves of fruit per day. Only Group B managed to maintain this change (p = 0.05).
Outcome measures were self-reported dietary intake (e.g., fruit and vegetable and fat consumption), attitudes toward a healthy diet (e.g., nutrition knowledge, psychosocial determinants of behavior), physiological outcomes (e.g., weight, body fat% and body mass index), physical activity and clinical markers such as cholesterol, blood sugar and blood pressure as well as sales data in canteens. In this review, we considered health-related outcomes as a broader category which incorporates physiological outcomes and clinical markers, as both of them are associated with the onset of NCDs [1].
The interventions included a range of different study designs. Thirteen were randomized controlled trials [12,13,16,17,19,23,[25][26][27][28]31,33,34] and the rest were interventions with various designs including controlled trials (longitudinal, non-randomized), non-randomized observational studies, quasi-experimental and pretest-posttest evaluations. Regardless of the design, all studies included an intervention and a control group, except for five [6,14,15,20,29] which examined the differences within the intervention group over time without having a control group.
Less than half of the studies (10 out of 25) applied a behavior change theory to facilitate health and food behavior change. The social cognitive theory (SCT) was used in three interventions [12,16,17], the transtheoretical model of behavior change (TMBC) in another three [14,17,18] and the social ecological model (SEM) in two [25,34]. Finally, one study applied the health belief model [10], one the 'attitude-social influence-(self-) efficacy model' (ASE model) [24] and one the theory of planned behavior (TPB) [23].
The number of participants ranged from 22 to 1294 and the length of the intervention varied from four weeks to 19.5 months. Four studies included male participants only [6,22,27,33], two studies included only female participants [16,18] and the remaining 19 included both male and female participants. Among them, 13 had mainly female participants [10,13,14,17,[19][20][21]23,25,26,28,29,34], while six had mainly male participants [12,15,24,[30][31][32]. Twelve studies were conducted in the USA, nine in Europe (three in Denmark, two in the UK and four in the Netherlands), one in Korea, one in Australia and two in Japan.
Based on the description of characteristics, 10 studies [6,12,14,17,[22][23][24][25]30,33] specifically mention the type of work as "office work" while the other 15 did not clearly state the term "office workers". In particular, seven studies include company employees [15,17,19,20,27,28,32], five university employees [10,16,18,26,29], three white-collar employees in health care organizations [13,14,34] and two incorporate blue and white collar workers with a higher percentage of white collars [21,31]. For a summary of study characteristics, see Tables 1-4. The literature search identified four different types of interventions that consisted of educational and environmental components, where environmental components were mainly providing healthy food in a work-related context. The interventions at the offices included web-based material, availability of food, provision of information in various ways, and a combination of environmental, educational and theory-based psychological approaches (i.e., multicomponent). These interventions assessed a range of outcomes, but this literature review focused only on three, i.e., dietary intake, dietary behavior and health-related outcomes (weight, Body Fat%, BMI, clinical markers such as cholesterol, blood sugar and blood pressure).

Web-Based Interventions
Eight of the 25 studies implemented a web-based intervention to promote healthy dietary practices [12][13][14][15][16][17][18][19]. The main components of this type of intervention were the provision of information and guidance on the major health promotion topics (educational sessions and material, webinars, advice, feedback, goal setting, articles, messages, books, newsletters, recipes, etc.). In addition to the basic intervention components, some participants received nutrition consultations via telephone [15] and an eating plan [15,16]. In five studies, self-reported data on dietary intake and lifestyle were collected [12][13][14]16,17]. In two studies, self-reported dietary intake data were collected along with measurements of anthropometric and clinical data conducted by qualified staff [18,19] and, in one study, qualified staff measured indirectly dietary intake via body composition and skin carotenoid level (biomarker for fruit and vegetable intake) [15].
Outcomes under review were diet, dietary behavior change, physical activity, body composition (body weight, percent of body fat, visceral fat level (cm 2 )), clinical biomarkers (blood pressure, fasting plasma lipids, etc.), aging beliefs, tobacco use, stress, and mental health.
Of the seven studies which collected data on diet outcomes, four studies found positive effects [13,14,16,18], of which one was based on pre-and post-assessment within the same group [30]. Improvements included increased intake of fruits and vegetables [13,18,30], reduced intake of saturated, trans fats and added sugars [13], increased intake of dairy products [16], and increased consumption of nuts, seeds, legumes and the monounsaturated fatty acids (MUFA): saturated fatty acids ratio (SFA)ratio [18].
Improved dietary behavior was reported in two studies [12,19] expressed as improvements in diet behavioral change self-efficacy (how confident they are that they can change their dietary practice), planning healthy eating (if they have a good plan for "maintaining a nutritious diet" and for "minimizing the amount of fats and sugars in my diet.") [12], dietary attitudes and dietary self-efficacy [19].
Positive changes in health-related outcomes (changes in body composition or clinical biomarkers) were observed in four studies [15,16,18,19].

Intervention Where Healthy Food Is Provided
Three of the 25 studies provide healthy food as a means to improve dietary habits and the health status of the workers [20][21][22]. Two strategies were used to achieve this goal; increased availability of healthy foods and provision of a ready-made meal with a predefined nutritional composition. The main food items made available at workplaces were free fruits placed in common areas [21], a balanced Japanese-style healthy lunch with sufficient amount of vegetables [22], and a canteen take-away meal for employees as well as for their families [20]. The assessments that the participants had to undertake were mainly anthropometric measurements [20][21][22], blood parameters [22] and 24 h dietary recall [20][21][22]. Two studies included self-reports of food intake [20,21] and one self-report of food intake and measurements conducted by qualified staff [22].
Only the study in which Japanese-style healthy lunches were provided examined health-related outcomes and found positive effects on blood parameters. In the group that ate the Japanese-style healthy lunch menu less than 50 times out of the total 61 times, plasma active ghrelin and desacylghrelin levels significantly increased and diastolic blood pressure significantly decreased. In the group that ate this lunch menu more than 51 times out of the total 61 times total cholesterol, LDL, levels significantly decreased and body fat percentage, systolic blood pressure and diastolic blood pressure significantly decreased [22].

Intervention Providing Information
Nine of the 25 included studies were limited to providing information to promote healthy dietary practices. Information was given by means of nutrition education sessions and counseling [6,10,[25][26][27][28][29], information sheets, brochures and leaflets [24,30] and placement of nutrition logo on cafeteria menu items [23]. Two studies included self-reports (dietary intake, health beliefs, and nutrition knowledge) [10,24], four contained data from self-reports (lifestyle parameters, health behavior, mental health, mindfulness) and measurements (anthropometric, clinical and exercise) conducted by qualified staff [6,[27][28][29]. Another study included sales data from 25 worksite cafeterias and self-reports the participants' BMI, behavioral determinants of food choice (i.e., attitude, self-efficacy, and intention) and if they used the logos to make healthy choices during lunch (in response categories ranging from one (= never) to five (= always) [23]. Finally, in two studies, measurements were conducted by qualified staff [25,26].
Outcomes included dietary intake (fruits and vegetables, fat and cholesterol), determinants of dietary behavior (self-efficacy, intention and attitude), body composition (body weight, body fat %, visceral fat), clinical biomarkers (blood sugar, LDL cholesterol), physical activity, mental health, and smoking.
Of the nine studies, three showed improvements in dietary practices [10,23,29], including increased fruit and vegetable consumption and lower fat, cholesterol, and energy intake.
A positive effect on dietary behavior was found in three studies [10,24,28]. In the first study, a significant effect was found on the perceived social support from colleagues regarding eating less fat [24]. In the second, it was shown that there were significant improvements in the perceived benefits of healthy nutrition practices and nutrition knowledge related to cardiovascular disease and cancer [10]. Finally, in the third study, in which employees were divided into three groups (two intervention and one control), the two intervention groups were more likely to report making lifestyle changes [28].

Multicomponent Interventions
Five studies provided a combination of components (i.e., multicomponent) including information, motivational prompts, and environmental changes [30][31][32][33][34]. Information was spread through the distribution of information sheets, brochures, leaflets, self-help manuals, posters, etc. [30,31,34], and educational programs [33], whereas environmental changes were carried out by increasing the availability of healthy foods [31,32]. Motivational prompts included footsteps on the floor and slim-making big mirrors [30], peer support in the form of modeling and education [32], workers' participation in program planning [34], and comments and impressions from family members and the counselor about the progress of the participant [33]. Four studies included self-reports (dietary intake, physical activity) [31][32][33][34] and one [30] included data from measurements conducted by qualified staff (blood parameters).
Positive health-related outcomes (decrease in LDL, total cholesterol, increase in the ratio between total and HDL-cholesterol (total/HDL), BMI, etc.) were reported in two studies [30,33].

Overall Findings
The present literature review presents available studies implementing dietary workplace interventions among office workers. Four different intervention types were identified and these were web-based, food-based, information and multicomponent programs. The most commonly used designs were information and web-based interventions, which are the least expensive ways to intervene.
Food-based interventions increased the availability of healthy foods or provided ready-made meals. Although none of them aimed to change diet behaviors per se, all of them were successful at improving the participants' dietary intake. However, one of them [22] aimed at reducing risk factors for the metabolic syndrome, with positive effects on blood pressure, serum lipids, and plasma ghrelin. Food-based interventions done in non-office settings report similar pattern of results [35,36]. For example, a study by Lachat et al. showed that providing fruits and vegetables in a university canteen contributed to a higher intake among students both at lunch and on an everyday basis [35]. Moreover, Backman et al. reported that blue collar workers who received fresh fruits and vegetables increased their consumption significantly compared to those in the control worksites [36]. The success of this type of intervention indicates that the provision of healthy food may be an easy and effective way to promote dietary changes.
Interventions that provided information only included nutrition counseling to help participants set priorities, establish goals, create individualized action plans and increase their awareness and knowledge about diet and health-related issues. This type of intervention was more effective at improving health-related outcomes than diet and dietary behavior. A potential explanation is that these interventions focus on improving both diet and physical activity, and part of the effect is from increased physical activity. A similar pattern of results was seen in an older study, not included in this review, that provided information about nutrition, which resulted in a reduction in weight and cholesterol among office workers [37]. Moreover, intervention studies done among non-office workers found that providing information resulted in positive changes. Briley et al. reported a reduction in weight and total cholesterol [38] and Aldana et al. demonstrated that educational courses in nutrition and physical activity had a beneficial effect and could potentially lessen the risks associated with common chronic diseases [39], thus confirming the results from the present review. Finally, most of the multicomponent interventions (a combination of healthy food, information, and motivational prompts) were more effective at improving dietary intake than health-related outcomes, and none of them aimed to change dietary behaviors. These interventions assessed a range of outcomes and the heterogeneity of reported findings made it challenging to summarize the results. Overall, positive effects in terms of increasing fruit and vegetable consumption, improved nutrient intake (e.g., decreasing fat and added sugars consumption, increasing fiber and protein consumption), increasing dietary knowledge, improving dietary behaviors (e.g., self-efficacy, planning healthy eating, attitudes towards healthy options) and aiding weight loss were reported. Improvements in health-related outcomes were also observed and were mainly in body composition and clinical biomarkers (total cholesterol, LDL, blood pressure, etc.).
Almost half of the multicomponent interventions focused on multiple health-related behaviors such as diet, physical activity, quitting smoking, reducing stress, etc., making it difficult to draw conclusions if dietary interventions alone or in combination with other health behaviors are more effective at improving health. Only a few studies aimed at improving diet exclusively, mainly by providing healthy food, with promising results. However, since these studies lasted between four weeks and 19,5 months, it is difficult to draw a conclusion regarding long-term effects.

Behavior Change Theories
Theories and models, relevant for the field of dietetics, are frameworks for helping practitioners understand external and internal issues and the dynamics that led to behavioral changes. The use of these frameworks provides a rationale for the selection of specific counseling strategies [40]. These theoretical frameworks are commonly used in intervention studies aimed at health promotion in workplaces. For example, the PACE (Physician-based Assessment and Counselling for Exercise) intervention aimed at enhancing moderate-intensity physical activity at the workplace was based on the TMBC and SCT [41]. Furthermore, in a review including twenty-one studies of worksite interventions addressing physical activity, behavior change theories were mainly used for counselling interventions and health education, with the TMBC being frequently applied [42]. Additionally, two large Dutch Randomized Controlled Trials (RCTs) which aimed at stimulating physical activity, embodied principles of cognitive behavioral therapy as well (e.g., modification of workers' irrational beliefs about their back pain) [43,44]. However, in the present literature review, only half of the studies were designed around these theories [10,12,[16][17][18][23][24][25]30,34].

Web Based
Most of the interventions that use behavior change theories and strategies to facilitate health and food behavior change were web-based. One of the most commonly used theories was SCT (also called social learning theory), which is based on the idea that people learn by observing other's social interactions, experiences, and outside media influences (includes techniques such as modeling skill training, self-monitoring, and contracting) [45]. The results from interventions based on this theory are mixed, but encouraging results regarding improvements in dietary intake and dietary behavioral change [12,17] were found as were moderate effects for weight loss [16].
Another commonly used theory was the TMBC that describes a sequence of cognitive (attitudes and intentions) and behavioral steps people need to take to change behavior. The model offers effective and specific strategies at various points in the process of change and suggests outcome measures including decision balance and self-efficacy. Appropriate application of strategies is dependent upon the participant's stage of change (precontemplation, contemplation, preparation, action, maintenance, and termination) [46]. Findings from the interventions based on this theory are promising with improvements in dietary intake and stages of readiness to eat healthier [17,18,30], and moderate with regards to weight loss [17].

Information
The theory of planned behavior (TPB) was one of the theoretical frameworks used among interventions that provided information as a mean to intervene. This theory suggests that the decision to behave in a certain way is the result of the likelihood of specific outcomes [40] and it was used successfully by Vyth et al. [23]. In their study, they added and labeled healthy options in worksite cafeterias expecting customers to increase healthy food consumption with the likelihood that they will benefit from this behavior.
Engbers et al. [24] applied the 'attitude-social influence-(self-) efficacy model' (ASE model) to measure psychosocial determinants of eating more fruit, and vegetables as well as less fat, and the model was also successful in affecting the reduction of fat intake. The ASE Model identifies the determinant 'social influence' instead of the determinant 'subjective norm'. Social influence embraces subjective norms, social support/pressure, and modeling [47].
The Health Belief Model (HBM) was applied in a theory-based worksite intervention, conducted by Abood et al. [10] and it was successful at improving health beliefs, nutrition knowledge, and dietary behavior. The HBM implies that health behaviors are determined by health beliefs and readiness to act [48]. Constructs central to the HBM consist of perceived susceptibility, perceived severity, perceived benefits, perceived barriers, and other mediating variables.
Improvements in metabolic risk factors were reported in one study conducted by Salinardi et al. [25] in which the SEM was used. The SEM is based on a theory related to the relationships between individuals, social groups, and the environment or community [40]. The SEM model was also applied in a large multicomponent randomized controlled trial conducted by Sorensen et al. [34] that included environmental aspects. The intervention comprised education, food tastings, family training, increased availability of fruit and vegetables, and food labeling. The study reported that the most intensive intervention (including the family component) was most successful and reported a significant increase in fruit and vegetable consumption.

Strengths and Limitations
A strength of the present literature review is the large number of articles included, of which most are randomized control trials and applied behavior change theories. However, there are limitations in this literature review that limit the generalizability of the results and the findings need to be considered with caution. Although we aimed to review dietary interventions per se in an office context, most of studies addressed a variety of health behaviors, making it difficult to disentangle the effect of dietary interventions alone. On one hand, improvements in diet could be linked to the dietary components such as environmental changes (e.g., provision of healthy food) and nutrition education and counseling. On the other hand, improvements could be linked to other parameters (physical activity, quitting smoking, reducing stress, etc.) that some of the studies focused on. Therefore, we cannot determine which of the above factors contributed exclusively to improvements in diet. The reviewed interventions were mainly carried out in the USA or Western Europe and these findings may not be applicable elsewhere. Bias regarding the target population may emerge. Only 10 of the 25 included studies specifically mention the term "office workers", while, in the rest of them, office work was assumed by the reviewers, since the papers described the working place and not the people working there. The limitations of the individual interventions are also limiting the literature review in its conclusions, such as the self-reporting of dietary outcomes, short intervention duration, limited or no follow-up periods, lack of control group in some studies, small sample size and a heterogeneous distribution of gender (women are more interested in nutrition) and the health status (i.e., participants at high risk may be more likely to want to change). The lack of rigorous study design, i.e., non-randomized and non-controlled trials, was a limitation in several of the included studies. However, some authors argue that randomized controlled trials are not the most appropriate designs for dietary interventions and that researchers should aim to increase efficacy, reach and uptake of interventions [49]. Another limitation of the literature review involves the issue of effectiveness. This literature review attempted to assess which types of intervention were more effective without assessing the quality and the cost-effectiveness of the studies. In this literature review, effective study is defined as a study in which a study detected a change in at least one of the outcomes under consideration such as dietary intake.

Future Research
Due to the small number of studies focused exclusively on office workers, there is a need for further research to identify the effectiveness of dietary workplace interventions in this target group. Moreover, the specific characteristics of office workers, with mainly sedentary behavior at work, should be considered when creating tailored messages and interventions adapted to this type of work place. Moreover, methods to assess long-term health and economic benefits are needed, as well as methods to better understand the individual components for change in the intervention, i.e., the 'how', 'why' and 'what' [50]. Finally, future intervention studies should also be conducted over longer periods of time to assess the long-term changes regarding dietary intake and behavior.

Conclusions
Diet plays an important role in the prevention of NCDs, and workplace dietary interventions have the potential to improve many aspects of dietary habits, dietary behavior, and health outcomes. However, there is no 'one design fits all'. Instead, one should focus on customized interventions, taking advantage of the specific work environment, such as interaction and support between colleagues, and taking into account eating habits inside and outside the office. Moreover, we suggest that future studies be more transparent when reporting results in terms of what did and did not work, as well as which approaches were well accepted by office workers. In this way, policymakers, employers and researchers can avoid making mistakes again.