Do dietary patterns explain high prevalence of cardiovascular risk factors among Pakistani urban adults? A cross-sectional study

Globally cardiovascular diseases (CVD) are a major contributor to chronic disease burden [1]. South Asians, in particular have a higher rate of acute myocardial infarction, and develop CVD at a younger age than individuals from other countries [2, 3]; CVD is becoming a leading cause of premature adult mortality in the region [4], mainly due to increased occurrence of CVD risk factors including central obesity, hypertension, and dyslipidemias among South Asians [3, 5]. Moreover, compared to other groups within the South Asian population, the prevalence of CVD has been found to be as high as 26.9 % among Pakistanis who are 40 years and older [2].

The quality of diet has been associated with the development of CVD [6]. Diet is a complex exposure variable and individual dietary factors (nutrients) are highly correlated with one another. In addition to studies evaluating individual nutrients, dietary patterns are now being employed to better understand diet and disease relationships. Dietary pattern analyses integrate consumption of individual foods and nutrients into meaningful groups or patterns [7–9]. Cluster analysis is a data-driven analytical method useful to identify dietary patterns within a homogenous group of people; which are then treated as independent variables for analysis of associations with markers of disease risk and health outcomes [10].

Studies using CVD biomarkers can provide important evidence on the relation of dietary patterns and disease risk [11, 12]. For example, risk of CVD can be largely predicted by measurement of plasma lipids. Large prospective studies from the United States [7, 13, 14] and Europe [15, 16] linking diet patterns and triglycerides, cholesterol, low-density lipoprotein, and high-density lipoprotein cholesterol have shown inconsistency in the effect of overall diet on disease risk.

Given the well-recognized link between diet and CVD, an important step is to identify dietary patterns that are associated with CVD in specific populations [17, 18]. As there are variations and differences in dietary intakes across different populations, it is likely that risk factors of CVD differ among Pakistani people as compared to other populations [5, 19]. Limited research has been conducted in Pakistan on dietary patterns and CVD risk factors [20, 21]. Previously we reported an associations between dietary pattern derived from factor analysis and socio-demographic, anthropometric, lifestyle characteristics and hypertension in Pakistani adults enrolled in the Control of Hypertension and Risk Attenuation (COBRA) study [22, 23]. In the current study, our aim is to derive dietary patterns using the cluster analysis method and investigate how these diet patterns are associated with CVD risk among Pakistani people aged 40 years and above.

South Asians are at higher risk of cardiovascular disease due to an increasing prevalence of its risk factors amongst them [35]. This cross-sectional study was undertaken to examine the association of diet patterns derived by cluster analysis with the prevalence of CVD risk factors (mainly obesity, lipid biomarkers, SBP and FBS) in Pakistani adults aged 40 years and older. Identification of overall diet trends that incorporates the interaction of different food items in a specific population is a more appropriate method to examine the relationship between diet and disease risk than focusing on individual foods or nutrients [7, 36]. Dietary pattern studies tend to identify at least one pattern or cluster that can be defined a healthier eating pattern, however, in some populations a typical healthy or unhealthy diet pattern may not exist but dietary behaviors might be characterized by different types of foods categorized as healthy or unhealthy within the similar diet patterns.

In Pakistan, limited research has been done to identify the different type of diets that are normally consumed by Pakistani people. In addition, currently no dietary guidelines, recommendations, or evidence-based dietary indices have been established by health and nutrition authorities in Pakistan. Therefore, studies using data driven methods including factor and cluster analysis are essential to identify existing dietary patterns among Pakistani people and inform public health initiatives in Pakistan. In our study, men and women following traditional Pakistani diet pattern (cluster 1) were characterized by high intake of foods including milk and milk products, potatoes and other vegetables, fruits, Pakistani bread, and bakery products with highest risk for obesity as compared to other diet patterns. Though, this diet pattern has some foods that are relatively healthier but because the usual intake in this group was highest for most foods, thereby increasing the total energy intake that may have been resulted in higher prevalence of overweight and obese adults in this pattern. Similar results were also observed in previous research studies [34, 37].

The relationship between dietary patterns and CVD risk could be manifold and complex in different populations [12, 38]. A large body of scientific evidence from observational studies [39], clinical trials [40], and genetic studies [41] have shown that lipids and glucose biomarkers may have causal relationship with CVD risk, though results have been inconsistent [7, 15]. Dyslipidemia, manifested by abnormal lipids with increased TC, LDL-C, and TG accompanied by a decrease in HDL-C, is considered a traditional risk factor for CVD [42]. It was difficult to compare our findings with earlier studies conducted in other populations because we were unable to identify a very distinct healthy or unhealthy diet pattern with which we could noticeably associate biomarkers of CVD risk. However, those following traditional Pakistani and fatty diet patterns (cluster 1 and 3) were relatively at a higher risk for LDL- cholesterol as compared to cluster 2. This could have been due to more food in general and high fatty food intake as reflected by these clusters. Similarly the risk for high TG was also observed in traditional Pakistani diet pattern (cluster 1). Previously Jafar has shown that factors including obesity, caloric-dense diet and sedentary lifestyle are likely to be associated with increased prevalence of CVD risk in Pakistani women [43]. In the current analysis those following pattern 3 were not consuming high levels of fatty foods including eggs, milk desserts, ice cream, and butter but had more CVD risk factors as compared to reference. The FFQ used in the assessment of food intake included a limited list of fatty foods reflective in a typical Pakistani diet, as the intent of the COBRA study was to determine only those types of foods that may pose a risk to hypertension. In addition, the FFQ was unable to capture the type and amount of fat used in cooking, and previous studies from Pakistan has shown an increased intake of saturated fats in daily cooking that may perhaps have contributed to an increased risk for those following pattern 3 [2, 43, 44].

Most data linking dietary patterns with biomarkers of CVD risk comes from observational studies. The Lyon Diet Heart Study, a randomized control trial was unable to show any association between lipid biomarkers of CVD risk (HDL-C, LDL-C, TG, and lipoprotein-a) and intake of diets characterized by fruits, vegetables, olive oil, and hard bread [45]. Thus, these results suggest that risk factors other than serum lipids may mediate risk between dietary patterns and CVD risk. We recommend caution in interpreting the relationship between the dietary patterns and biomarkers as ours was a cross-sectional study.

In our study, the prevalence of subjects with elevated SBP was found to be relatively high (68.2 %), though subjects who self-reported hypertension were excluded. Distributions of these participants were highest (71.8 %), across moderate diet pattern, despite the fact that the frequency of intake of many food items was much less than in other two clusters. Also notable was the fact that certain Pakistani foods that are supposedly proposed to increase blood pressure for example paratha, tandori nan, salty lassi, biryani etc. were eaten much less frequently in this group as compared to other cluster groups. In contrast, subjects in cluster 1 showed a protective effect on SBP risk that cannot be explained by more frequent consumption of above food items. This unusual observation could be explained by the fact that intake of fruits and vegetables along with some unhealthy food were seen in this group (Traditional Pakistani diet, cluster 1). Nevertheless, similar results have also been observed by Sadakane et al.[46], who has reported that the Western diet pattern was not associated with higher systolic and diastolic blood pressures in the Japanese population. We recommend further exploration of these findings in order to improve our understanding about the association between western type of diet in a Pakistani population and blood pressure.

This study is notable because of its large sample size and a high response rate (88.38 %). The extensive information gathered from the study subjects makes our study findings more informative and may have substantial implications for other similar populations in South Asia.

However, the study has several limitations. First, the results cannot be generalized to other regions of Pakistan as the study group was from one major city only and therefore cannot be assumed to be representative of all Pakistani people. However, participants from the COBRA study reflected almost all major ethnic groups living in Pakistan. Second, it was a cross sectional study, therefore, causality of the relationship between the dietary patterns and CVD risk factors cannot be fully ascertained. In addition to the nature of the study, recall bias was another concern because abnormal lipids may have changed participants’ diet patterns or led to a biased reporting of dietary habits. This issue, however, was mitigated by the exclusion of patients with self-reported diabetes, hypertension, stroke and heart disease from the study analyses. Third, we used a modified FFQ with limited food lists which was not a validated questionnaire for Pakistani population; though it was pretested in a similar sample population prior to its administration in terms of being understood by the population, and for capturing the typical dietary intake of the study population was done. Also, the FFQ did not require the participants to report the portion size or amount of food; therefore it precluded us from adjusting our regression model for total energy intake. Though, an alternative adjustment was done by adjusting the regression model for physical activity. It was difficult to quantify misreporting based on the available data that could be due to several reasons that we were unable to capture due to methodological limitations of secondary analysis. Fourth, since this was a study in which biomarkers were assessed, we need to consider many factors that may affect the appropriateness and sensitivity of biological samples in epidemiologic studies of dietary intake. A single sample may not have been be a representation of long term intake, especially if there is lot of variation in an individual’s diet. In addition, there are collection and measurement issues that may have affected the results in the current study [12].

Cluster analysis is a useful exploratory data driven technique for deriving dietary patterns in populations where fundamental dietary patterns do not exist. While identifying data driven or posteriori dietary patterns, many arbitrary but important decisions are made by the researcher, such as consolidation of food items into food groups, the number of patterns to derive from the data, labeling of patterns etc. This can make it difficult to compare and interpret the findings with other studies. However the exposure groups derived from cluster analysis are homogenous and non-overlapping, which is helpful in studies explaining relationship between diet patterns and risk for diseases [10]. As dietary guidelines for Pakistan get established, future studies of guideline-based indices and CVD risk will be possible and well warranted.

The present study shows that some of the CVD risk factors including obesity and hypertension are highly prevalent among low income urban Pakistani adults. The study further provides some evidence that CVD risk factors could be linked with certain type of diet patterns but not consistently for all CVD risk factors as well as in all population groups. However, these results are important for Pakistan as people here are already susceptible to a high prevalence of obesity, hypertension and dyslipidemia [47]. Effective Public health strategies and multiple lifestyle change initiatives are required against obesity and hypertension among Pakistani adults to avert rise in CVDs.