Study population and data collection
Yazd Health Study (YaHS) recruitment phase data was used for this cross-sectional study. YaHS was initiated among the adult population living in Yazd Greater Area, with 10000 participants between the ages of 20-70 years old). Established in November 2014 and containing two phases, YaHS at first, randomly selected 200 clusters according to the city post codes. Then, the interviewers set up a meeting time with the residences at each of their assigned addresses. At last, as the interviewers visited the neighborhood of the first addressee based on the study protocol to fill in the questionnaire forms .In the present research, out of 3748 available cases with data on dietary intakes and main variables associated with metabolic syndrome, 2896 participants were considered according to exclusion criteria (including having a history of cardiovascular disease, diabetes and cancer).
Demographics data, anthropometrics (weight, height and waist circumference), socioeconomic status, education, physical activity, tobacco smoking and dietary habits in addition to biochemical assessments including; fasting blood glucose, triglyceride and HDL cholesterol levels were also carried out.
The present study was approved by the Ethics Committee of Shahid Sadoughi University of Medical Science (IR.SSU.MEDICINE.REC.1395.287). Written informed consents were obtained from all the participants.
In general, all the required information on participants’ dietary habits, anthropometric indices measurements, blood test results, blood pressure measurement and confounding factors consisting of socioeconomic status, history of chronic diseases and physical activity status, were extracted and merged from YaHS database .
We aimed at obtaining accurate information on some dietary habits noted by participants via a questionnaire . These items were as follows; i) sweetened drinks (fruit juices, artificially or homemade sweetened beverages) with frequency consumption of not at all, less than once per week, once or more per week, ii) fast foods consumption with frequency of not at all or few times per year, 1-3 times per months, once or more per week, iii) breakfast consumption as not at all in frequency, once per week or more than once per week , iv) sugar cubes with the serving intake of not at all, 1-2 cubes per day and more than 2 cubes per day.
Diagnosis of metabolic syndrome
National Cholesterol Education Program and Adult Treatment Panel III criteria (NCEP) present the definition of MetS in the current study [37-39]. To be diagnosed with at least 3 risk factors out of the five following cases, means a participant has metabolic syndrome if: i) Triglyceride (TG) above 150 mg/dl or consuming triglyceride lowering agents (hyperglyceride); ii) high density lipoprotein-cholesterol (HDL-C) level of less than 40 mg/dl in men and less than 50 mg/dl in women or any kind of pharmacological treatment; iii) Systolic blood pressure above 130 mmHg and diastolic blood pressure above 85 mmHg (hypertension); iv) Fasting blood glucose above 100 mg/dl or usage of pharmacological treatment as a control from blood sugar; and v) and waist circumference (WC) above 91.5 cm in men and 85.5 cm in women (adopted for only Iranian population) .
Evaluation of anthropometric indices
Weight was recorded with participants wearing lightweight clothing and no shoes using a digital scale (Model BF511, Omron Co. Karada Body Scan, Osaka, Japan) with the precision of 0.1 kg. A non-stretchable tape meter with the precision of 0.5 cm was used to measure height with lightweight clothing and no shoes and with their heels, hip, shoulder and head touching the wall. Body mass index (BMI; weight (kg) / height (m2)) was calculated from measuring height and weight. Waist circumference was also measured by a tape in the horizontal plane midway between the iliac crest and the rib cage with the precision of 0.1 cm.
Blood pressure measurement
Systolic and diastolic blood pressures were measured in the sitting position by an automatic digital blood pressure monitor (Reister Germany). Each measurement was repeated for two times after every 5-minute interval.
Data on serum level of fasting blood glucose (FBG) (mg / dl), total cholesterol, triglycerides, low density lipoprotein-cholesterol (LDL-C) and high density lipoprotein-cholesterol (HDL-C) were measured and collected. The equipment used in this study included a calibrated Ciba Corning auto-analyzer device (Ciba Corp., Basle, Switzerland (and Pars Azmoon company kits to asses fasting blood glucose and triglyceride after centrifuging and bionic kits as an analyzer for HDL cholesterol.
Physical activity assessment
For ascertainment physical activities the Iranian Short Version of International Physical Activity Questionnaire (IPAQ) was given to the participants [41, 42]. Physical activity levels of each participant were categorized as active and inactive based on the guideline of short form of IPAQ .
All statistical analyses were performed using SPSS version 24 (SPSS Inc., Chicago, IL, USA) and to show the qualitative variables, they went under a frequency and percentage discretionary. Multiple-logistic regression was used to examine the association between dietary habits and MetS. The lowest frequency or serving indicates a reference for all the models and adjustments of the confounding factors which are as follows: Age (20-29, 30-39, 40-49, 50-59, 60-69 years), educational level (secondary school and lower, high school, diploma and graduate diploma, bachelors, masters and PhD), history of chronic diseases (yes/no, including : hypertension, diabetes, cardiovascular disease, cancer, depression, dyslipidemia), smoking history (yes/no), physical activity level (inactive and active), and BMI (continuous).