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Brief Report  |   March 2019
Prior Knowledge of the Mediterranean Diet Is Associated With Dietary Adherence in Cardiac Patients
Author Notes
  • From the Centers for Health Sciences (Student Doctor Greiner and Dr Croff) and Rural Health (Dr Wheeler) at Oklahoma State University in Tulsa and the College of Health Education at Oklahoma State University in Stillwater (Dr Miller). 
  • Financial Disclosures: None reported. 
  • Support: None reported. 
  •  *Address correspondence to Benjamin Greiner, OMS III, Center for Health Sciences, Oklahoma State University, 429 Willard Hall, Stillwater, OK 74078-1001. Email: ben.greiner@okstate.edu
     
Article Information
Cardiovascular Disorders
Brief Report   |   March 2019
Prior Knowledge of the Mediterranean Diet Is Associated With Dietary Adherence in Cardiac Patients
The Journal of the American Osteopathic Association, March 2019, Vol. 119, 183-188. doi:https://doi.org/10.7556/jaoa.2019.029
The Journal of the American Osteopathic Association, March 2019, Vol. 119, 183-188. doi:https://doi.org/10.7556/jaoa.2019.029
Web of Science® Times Cited: 1
Abstract

Context: Cardiovascular disease (CVD) is the leading cause of death in the United States, and cardiovascular events have been shown to be reduced and prevented when patients follow the Mediterranean diet.

Objective: To understand how familiarity with the Mediterranean diet affects dietary habits in cardiology patients by using social cognitive theory.

Method: This cross-sectional study included patients at a metropolitan outpatient cardiology clinic in Oklahoma. A survey was used to analyze patient knowledge of the Mediterranean diet. Patients were separated into low–, medium–, and high–diet adherence groups based on their daily consumption of fruits, vegetables, fish, whole grains, and nuts. Multinomial logistic regression was used to analyze patients’ knowledge of Mediterranean diet principles with dietary adherence.

Results: A total of 337 patients were included in the study. Patients with a college education, patients reporting familiarity with the diet, and women were 6.7, 4.0, and 3.2 times as likely, respectively, to have strong adherence to the Mediterranean diet.

Conclusion: The finding that familiarity with the Mediterranean diet was closely associated with adherence to its principles indicates that patient education on heart-healthy diets may improve the eating habits of patients, especially patients at risk for cardiac events.

Cardiovascular disease (CVD) is the leading cause of death in the United States and is associated with an estimated 610,000 deaths per year.1 Cardiovascular disease has an annual direct economic impact on the United States of $272.5 billion and an indirect economic impact of $171.7 billion.2 The costs associated with CVD care are estimated to be 17% of the overall national health care expenditures. A 2010 study by Nichols et al3 reported that the mean annual health care cost for individual patients directly attributed to CVD was $18,953. Given the rising costs of health care and inflation, this value is likely underrepresented. Cardiovascular disease has substantial effects on the physical and financial health of people in the United States, and these effects support the urgent need for improvements in CVD care and prevention. 
Strong empirical evidence supports that dietary improvements characteristic of the Mediterranean diet—specifically, decreasing intake of saturated fat and increasing consumption of unsaturated fats, fruits, and vegetables—reduces the risk of CVD and cardiac events, as shown by the Prevención con Dieta Mediterránea (PREDIMED) trial,4 the Lyon Diet Heart Study,5 and multiple systematic reviews.6-8 Estruch et al4 found that people consuming a Mediterranean diet vs a reduced fat diet were 30% less likely to have a major cardiac event as evidenced by a hazard ratio of 0.7. More recent studies substantiate improved cardiovascular health from specific foods within the Mediterranean diet, including olive oil, fruits, vegetables, and legumes.9 Cardioprotective effects are also observed in vegetarian10 and Dietary Approaches to Stop Hypertension (DASH) diets.11 
Furthermore, a plant-based diet has been shown to reverse coronary artery disease, as measured by angiography, in 2 prospective studies.12,13 Thus, these diets can be considered as alternatives for patients with ethnic or dietary concerns that limit their ability to adhere to the Mediterranean diet. Physicians have multiple heart-healthy diet options to inform patients about, making dietary education a patient-specific modality of reducing CVD. In response to the mounting evidence, new guidelines were issued by the American Heart Association recommending decreased intake of dietary salt, red meat, and processed foods, with increased intake of poultry, fish, legumes, nontropical vegetable oil, fruits, vegetables, nuts, and whole grains.14 
Given the mortality rate attributed to CVD and the benefits of diet modifications, one solution is to prescribe a diet change. However, about half of individuals with chronic illnesses like CVD who make a health behavior change fail to maintain it.15 Therefore, it is important to better understand the influences associated with sustained behavior change and how patient education affects the outcome. 
Social cognitive theory has been used to study the motivational mechanism that underlies diet behavior change.16 The theory proposes that one's ability to use self-reflection and personal judgment to self-regulate behavior predicts whether a person is able to start and successfully maintain behavior change. Further, self-regulation and self-efficacy are manipulated by intrinsic and extrinsic beliefs—a result of past experiences, the environment, and social norms. For example, successful adoption of healthier dietary behavior begins with internal reflection, followed by consideration of specific changes that must be incorporated and then consideration of the long-term feasibility of these changes. These processes are influenced by prior knowledge, past experiences, and self-perception. 
The purpose of this study was to analyze how prior knowledge of the Mediterranean diet affects the ability to maintain the diet in a patient with known CVD. Prior knowledge is a proximal determinant to the self-regulation process and reflection of effective patient education. This study focused on adherence to the Mediterranean diet tenets as defined in the American College of Cardiology and the American Heart Association guidelines.14 We hypothesized that study participants who reported familiarity with the Mediterranean or heart-healthy diet would consume healthier food than participants not reporting familiarity with the diet. Additionally, we hypothesized that a majority of patients with CVD would report familiarity with the diet as a result of patient education. 
Methods
The research proposal for this cross-sectional study received approval from the Oklahoma State University and Hillcrest Medical Center institutional review boards. Surveys were distributed from a metropolitan outpatient cardiology clinic in Oklahoma to a sample of patients with known CVD history or patients who were considered at risk for CVD. The cardiology patients were asked to participate in the study following a convenience sample protocol as they arrived for their appointments. The researcher explained the purpose of the study and provided a paper copy of the Food Beliefs Survey to the patient. Completion of the survey was voluntary and acted as the informed consent for research use. Patients were not educated on the Mediterranean diet or told to follow a specific diet in preparation for this study. Inclusion criteria included all patients aged 18 years or older attending cardiology appointments. Exclusion criteria included patients younger than 18 years, pregnant women, and prison inmates. 
Demographics were measured according to Centers for Disease Control and Prevention guidelines,17 and a modified form of the Food Beliefs Survey was used to measure the study objectives. The Foods Beliefs Survey was validated and demonstrated good reliability in multiple studies,16,18,19 but it had not been tested on the population of interest in the current study. The survey was not revalidated after being modified to study the Mediterranean diet specifically. 
Participants were asked to respond “Yes” or “No” to the question, “Are you familiar with the Mediterranean (heart-healthy) diet?” Respondents were asked to answer specific questions about their diet rather than using a 24-hour food recall questionnaire. The authors developed a scoring system based on recommended daily consumption amounts using the US Department of Agriculture report on Mediterranean diet eating patterns.20 Self-reported diet patterns were summed across Mediterranean diet categories (0=less adherent, 1=moderate adherence, 2=optimal adherence) to produce a total score that ranged from 0 to 13. Higher scores indicate a stronger adherence to the Mediterranean Diet food group consumption recommendations. Based on the scoring system developed by the authors, participants were placed into 3 different groups: low dietary adherence (score, 1-4); moderate dietary adherence (5-7); and high dietary adherence (≥8). These categories were selected based on the distribution of diet scores in this study. 
Results
Three hundred seventy-five surveys were distributed to a sample of patients with known or highly probable CVD history from a metropolitan outpatient cardiology clinic in Oklahoma. Fifteen surveys were not returned and 23 had less than two-thirds of the survey completed. A total of 337 surveys were retained for analysis. Three hundred respondents completed the gender question, of whom 48.7% were men. The mean (SD) age was 63.6 (13.5) years. 
Of the 318 participants completing the race question, most were white (245 [77.0%]). The largest minority population was Native American (44 [13.8%]), followed by black (19 [6.0%]), Hispanic (5 [1.6%]), and Asian (3 [0.9%]). Nineteen participants did not select a race or ethnicity. Descriptive statistics revealed that 100 of the 337 participants (29.7%) reported being familiar with the Mediterranean or other heart-healthy diet. 
A multinomial logistic regression was conducted to determine if adherence to a heart-healthy diet, measured along a continuum and collapsed to 3 categories (low, moderate, and high), was associated with various demographic variables, including gender, race, education, and familiarity with the Mediterranean diet. Results showed a significant association among demographic variables and adherence. The overall model was significant (χ212=37.79, P<.001; Table). When comparing high adherence with low adherence, gender (Wald χ21=6.62; P=.01), education (χ21=11.02; P=.001), and familiarity with the Mediterranean diet (χ21=5.88; P=.015) were significantly associated with high adherence to a heart-healthy diet. Participants who obtained at least a college education were 6.7 times as likely to report high adherence compared with those with a high school education. Women were 3.2 times as likely as men to strongly adhere to a heart-healthy diet. Finally, patients who were familiar with the Mediterranean diet were 4.0 times as likely to report strong adherence compared with patients not familiar with the diet. 
Table.
Multinomial Logistic Regression Showing Demographic Variables and Adherence to Mediterranean Diet (N=337)
β(SE) 95% CI OR
Moderate Adherence vs Low Adherence
    Intercept 2.98 (0.63)d
    Men −0.42 (0.37) 0.32-1.36 0.66
    Racea  
      Native American −0.69 (0.47) 0.66-1.27 0.50
      Black 0.18 (0.80) 0.25-5.78 1.20
    Educationb
      High school −0.54 (0.48) 0.23-1.49 0.59
      Some college 0.01 (0.56) 0.29-2.61 0.87
    Not Familiar With Diet −0.94 (0.52) 0.14-1.07 0.39
    High Adherence vs Low Adherence
    Intercept 3.08 (0.67)d
    Men −1.17 (0.45)d 0.13-0.76 0.31
    Racea      
      Native American −0.82 (0.62) 0.13-1.47 0.44
      Black −0.01 (0.99) 0.14-6.86 0.99
    Educationb      
      High School −1.89 (0.57)d 0.05-0.46 0.15
      Some College −0.77 (0.63) 0.14-1.59 0.46
    Not Familiar With Diet −1.39 (0.58)c 0.08-0.77 0.25

a Race compared with white (P<.05).

b Education compared with college graduate (P<.01).

c P<.05.

d P<.01.

Abbreviation: β(SE), unstandardized β and SE.

Table.
Multinomial Logistic Regression Showing Demographic Variables and Adherence to Mediterranean Diet (N=337)
β(SE) 95% CI OR
Moderate Adherence vs Low Adherence
    Intercept 2.98 (0.63)d
    Men −0.42 (0.37) 0.32-1.36 0.66
    Racea  
      Native American −0.69 (0.47) 0.66-1.27 0.50
      Black 0.18 (0.80) 0.25-5.78 1.20
    Educationb
      High school −0.54 (0.48) 0.23-1.49 0.59
      Some college 0.01 (0.56) 0.29-2.61 0.87
    Not Familiar With Diet −0.94 (0.52) 0.14-1.07 0.39
    High Adherence vs Low Adherence
    Intercept 3.08 (0.67)d
    Men −1.17 (0.45)d 0.13-0.76 0.31
    Racea      
      Native American −0.82 (0.62) 0.13-1.47 0.44
      Black −0.01 (0.99) 0.14-6.86 0.99
    Educationb      
      High School −1.89 (0.57)d 0.05-0.46 0.15
      Some College −0.77 (0.63) 0.14-1.59 0.46
    Not Familiar With Diet −1.39 (0.58)c 0.08-0.77 0.25

a Race compared with white (P<.05).

b Education compared with college graduate (P<.01).

c P<.05.

d P<.01.

Abbreviation: β(SE), unstandardized β and SE.

×
Discussion
Social cognitive theory states that prior knowledge and past experiences, developed in part by patient education and dietary counseling, affects patient dieting capabilities.16 Modulation of behavior occurs through self-regulation, expected outcomes, and self-efficacy. The present study supported the hypothesis that prior knowledge of the Mediterranean diet has a positive effect on diet quality. Patients in the high–dietary adherence groups were significantly more likely to be familiar with the heart-healthy diet than the low– and moderate–dietary adherence groups. Therefore, patient education on heart-healthy diets would likely improve healthy diet consumption. 
The numbers of participants completing the race question differed from the racial and ethnic proportions expected to be seen in the United States, according to a 2017 American Heart Association report.21 The report found that CVD rates, which included hypertension, stroke, and myocardial infarction, were 37.4% in men and 35.9% in women. The American Heart Association report also showed the CVD incidence for both sexes to be 36.4% in whites, 46.9% in blacks, 32.3% in Hispanics, and 29.0% in Asians between 2011 and 2014. In addition, we found that patients familiar with the Mediterranean diet were 4 times as likely to report a strong adherence to the diet. Given this finding, it is concerning that less than one-third of the participants were familiar with heart-healthy foods and that the prevalence of heart disease was elevated in participants with lower levels of education.21 Our findings indicate that further efforts need to be made toward educating patients who have or are at risk for CVD. In addition, these findings represent the need for optimizing the osteopathic tenet of treating the whole person through primary and secondary dietary interventions as opposed to only treating the symptoms of CVD with coronary artery bypass grafting and angioplasty with stenting. 
Alternative diets shown to reduce the morbidity and mortality of CVD include the DASH diet11 and vegetarian diet.10,12 To our knowledge, unlike strict vegetarian diets, the Mediterranean diet has not been shown to reverse coronary artery disease as proven by angioplasty.12 Thus, other diets may be better for reducing morbidity and mortality from cardiovascular events, although consideration for patient compliance with stricter diets must be recognized. Physicians have a number of dietary options to inform patients about and an opportunity to promote a heart-healthy diet specific to the individual that may boost dietary adherence. 
The observational nature of this study could not allow for cause and effect conclusions to be made. It is unclear whether educating patients on the Mediterranean diet will improve their diet quality. Moreover, this study did not account for patients with gluten intolerance who already require a modified whole grain diet or patients who use anticoagulation therapy with warfarin and require a modified diet of vegetables and limited intake of red wine. The diet scores would have been skewed for participants who could not accumulate points in certain categories because of their current diet modification. It is possible that the patients in these 2 groups were not familiar with the Mediterranean diet because they were educated on their case-specific diets. 
Additionally, due to the Health Insurance Portability and Accountability Act of 1996, patients could not be verified to have CVD. Thus, the patients in this study could only be classified as “highly probable” for having CVD because the majority of patients in this outpatient clinic were cardiology patients or had a physician referral for cardiology-specific care. Recall bias may have also limited the validity of this study because of the use of self-reported food recall over the previous 24 hours. Finally, this study focused on the Mediterranean diet and did not consider patient knowledge of the DASH, vegetarian, or other diets that also reduce the risk for cardiac events. This limitation may have had a negative effect on the clinical significance of the study, as it prevented the inclusion of diets other than the Mediterranean variation. 
Conclusion
Although not measuring the effectiveness of the Mediterranean diet, this study showed that patients’ knowledge and familiarity with the Mediterranean diet was associated with adherence to its principles. This study also found that having a college education and being a woman was associated with strong adherence to the Mediterranean diet. Additionally, few patients indicated having previous knowledge of the Mediterranean diet, which offers vast opportunities for improving cardiovascular care through educating patients on following a heart-healthy diet. Primary care physicians would be excellent resources for informing patients of heart-healthy diets because they have strong ties with patients and their families, and that relationship may improve the education process. Further studies should be conducted on the relationship between prior knowledge, dietary adherence, and diet quality in interventional studies, which offer stronger support for the theory that patient education and prior knowledge act as proximal determinants to dietary behaviors. 
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Table.
Multinomial Logistic Regression Showing Demographic Variables and Adherence to Mediterranean Diet (N=337)
β(SE) 95% CI OR
Moderate Adherence vs Low Adherence
    Intercept 2.98 (0.63)d
    Men −0.42 (0.37) 0.32-1.36 0.66
    Racea  
      Native American −0.69 (0.47) 0.66-1.27 0.50
      Black 0.18 (0.80) 0.25-5.78 1.20
    Educationb
      High school −0.54 (0.48) 0.23-1.49 0.59
      Some college 0.01 (0.56) 0.29-2.61 0.87
    Not Familiar With Diet −0.94 (0.52) 0.14-1.07 0.39
    High Adherence vs Low Adherence
    Intercept 3.08 (0.67)d
    Men −1.17 (0.45)d 0.13-0.76 0.31
    Racea      
      Native American −0.82 (0.62) 0.13-1.47 0.44
      Black −0.01 (0.99) 0.14-6.86 0.99
    Educationb      
      High School −1.89 (0.57)d 0.05-0.46 0.15
      Some College −0.77 (0.63) 0.14-1.59 0.46
    Not Familiar With Diet −1.39 (0.58)c 0.08-0.77 0.25

a Race compared with white (P<.05).

b Education compared with college graduate (P<.01).

c P<.05.

d P<.01.

Abbreviation: β(SE), unstandardized β and SE.

Table.
Multinomial Logistic Regression Showing Demographic Variables and Adherence to Mediterranean Diet (N=337)
β(SE) 95% CI OR
Moderate Adherence vs Low Adherence
    Intercept 2.98 (0.63)d
    Men −0.42 (0.37) 0.32-1.36 0.66
    Racea  
      Native American −0.69 (0.47) 0.66-1.27 0.50
      Black 0.18 (0.80) 0.25-5.78 1.20
    Educationb
      High school −0.54 (0.48) 0.23-1.49 0.59
      Some college 0.01 (0.56) 0.29-2.61 0.87
    Not Familiar With Diet −0.94 (0.52) 0.14-1.07 0.39
    High Adherence vs Low Adherence
    Intercept 3.08 (0.67)d
    Men −1.17 (0.45)d 0.13-0.76 0.31
    Racea      
      Native American −0.82 (0.62) 0.13-1.47 0.44
      Black −0.01 (0.99) 0.14-6.86 0.99
    Educationb      
      High School −1.89 (0.57)d 0.05-0.46 0.15
      Some College −0.77 (0.63) 0.14-1.59 0.46
    Not Familiar With Diet −1.39 (0.58)c 0.08-0.77 0.25

a Race compared with white (P<.05).

b Education compared with college graduate (P<.01).

c P<.05.

d P<.01.

Abbreviation: β(SE), unstandardized β and SE.

×