In the present study which analyzed dietary data collected from four surveys over the course of a decade (from 2006 to 2017), we derived three dietary patterns using factor analysis which was mostly centered on these food groups: a Healthy dietary pattern characterized by vegetable, fruit, dairy products, liquid oil, and nuts and seeds, a Western dietary pattern featured by soft drink, snack and dessert, meat, refined grain, and solid fat intake, and a Mixed dietary pattern highlighted by tea and coffee, and simple sugars. Our findings indicated that the structure of these dietary patterns did not seem to be stable over a decade. It means that the type of food groups that population have chosen to eat in combination had changed since 2006. This revealed a secular trend in dietary patterns including an emerging adherence of study population to Mixed dietary pattern, maintenance of Healthy dietary pattern, and a decline of Western dietary pattern.
Most of the previous epidemiological studies which focused on dietary patterns, have analyzed the relation of dietary pattern with risk of chronic diseases [16–21], and less of them investigated the secular trend of dietary patterns over the time[9, 10, 22, 23]. Mostly three common dietary patterns have been identified throughout these investigations. Healthy or Prudent dietary pattern which is mostly based on fruit, vegetable, dairy product, and liquid oil, Unhealthy or Westernized dietary pattern which is mostly characterized by solid fat, snack, soda, and meat; however, the third one which mostly named by modified, new or mixed dietary pattern, differ in each study with different factor loading and food items. Healthy and Western dietary patterns loaded in the current study is mostly similar to the results of other studies[9, 21]. Adherence of our study population to the three dietary patterns is similar to the result of Korean population, in which the number of participants following the Western dietary pattern declined, and the new dietary pattern increased in population over time .
According to the results of this study, energy intake of study population remained stable since the first survey. However, the percent of energy from carbohydrate and protein intakes increased and percent of energy from fat and all its subtypes (saturated, mono- and polyunsaturated fatty acids) decreased. People have become increasingly aware of the health benefits of vegetable oils and it seems that the source of fat intake has been changed during the last decade and there are a significant shift from intake of solid fat to the liquid oil . Likewise, the sources of protein intake has been changed from animal to plant based including legumes.
In term of the trend in food consumption, our findings indicated that fruit and vegetable intake has remained consistent. It seems that policy approaches must be considered to increase fruit and vegetable intake, as consumption of these food groups is hardly possible for the populations with low income. Whole grain, has increased significantly since the first survey, which was in contrast with the trend of other MENA region countries . In the current study, intake of meat as a protein source was stable over the last decade, which was in contrast to the results of other Asian country including China and India where meat intake had increased since the westernization . It is important to note that with the growing rate of urbanization, study population have eaten more snacks and desserts. One of the important points of current study is that the dietary dairy intake decreased significantly throughout the surveys. This result has been proven by the World Health Organization STEP wise approach to Surveillance (STEPS), which indicated that only near the 18 percent of Iranian population meet the appropriate amount of dairy intake .
According to the results of current study, Mixed dietary pattern has increased since the survey 1. This dietary pattern consist of simple sugar, tea and coffee, and whole grain which is mostly similar to the traditional dietary pattern of Iranian population. Simple sugar and tea and coffee were loaded in all four surveys and it shows a deeply rooted of these food items in the traditional dietary pattern of Iranian culture. Interestingly, in the second and mostly third surveys unhealthy food items such as refined grain, and solid fat was added to the Mixed dietary pattern and this may be influenced by modified Iranian meals like western style dinner. The traditional Iranian diet is wheat-based. Tea is the major beverage and dairy products such as yoghurt and cheese was consumed widely ; however, the consumption of dairy products decreased since last decade. It is noteworthy that about 38% of our study populations tried to maintain a Healthy dietary pattern; however, the intake of food groups have been changed and they accepted Western-style foods according to changing environmental factors. It appears that Iranian modified their dietary pattern, in another words it is not pure westernized but lots of unhealthy foods was added to the traditional dietary patterns of study population.
The strength of the present study is the large sample size, and the longitudinal design of the study, so we could track changes in dietary pattern individually. Moreover, the food frequency questionnaire which help to capture food groups that are only episodically consumed and the tool did have a validity test. Besides, we believe that our comparisons between years were not affected by the cohort effect, not only because all the subjects were included in at least two surveys but also because we adjusted all the results by age in the first survey.
One of the limitations of the present study is that some food groups including dairy products, fast foods, and meat intakes were not separated into subgroups. For this reason, it is not clear that putting these food groups in one of the three dietary patterns is because of which food item. For example meat consist of egg, red meat, poultry, and fish. Another important limitation is that the number of foods available in the food supply exceeds by far the number of those available in food composition tables so the present study was unable to capture all the changes in dietary intake, particularly of processed packaged foods. Recall bias was also an inevitable problem when asking participants to remember and report dietary intakes.