Study design and participants
The present cross-sectional study was carried out among Iranian adults, aged between 18 – 59 years, referred to five different Health centers in Tehran region. These centers were selected by chance, and the same number of subjects were randomly chosen from each center. Inclusion criteria were; age between 18-75 years and willing to participate in the study. The exclusion criteria were; suffering from kidney, liver, and lung diseases, and other disorders that negatively affected the cardiovascular or respiratory system health, or infectious and active inflammatory diseases, pregnancy, lactation, routine use of supplements or drugs, like weight loss, sedative drugs, thermogenic supplements such as caffeine and green tea, etc. The study guidelines were approved by the ethical committee of Tehran University of Medical Sciences and under the Declaration of Helsinki. After informing subjects in detail about the study aims, they signed written informed consent before the start of the study.
Demographic data
A demographic questionnaire was used to collect data on age, gender, education level (illiterate, under diploma, diploma, bachelor degree and above), marital status (single, divorced, married), smoking (employed, housekeeper, retired, unemployed), and occupation (never smoked, quit smoking, low smoking, heavy smoking).
Physical activity
A validated International Physical Activity Questionnaire (IPAQ) was utilized to evaluate the physical activity levels of participants. Obtained amounts were considered based on Metabolic Equivalents (METs) and sorted into three classes (low: <600, moderate: 600 to <1500, and high ≥1500 MET-minute/week) (11).
Anthropometric and blood pressure assessment
Weight was measured with light apparel and without shoes utilizing a digital scale (808Seca, Germany) to the closest of 0.1 kg and the height was assessed while standing and keeping the shoulders and hips against the wall without shoes, using a stadiometer (Seca, Germany) with an exactness of 0.1cm. Body mass index (BMI) was calculated as weight divided by squared height and presented as kg/m2. Waist circumference (WC) was measured between the lower rib and iliac crest, using a tape meter, according to standard guidelines. Waist to hip ratio (WHR) was determined as waist circumference (cm) divided by hip circumference (cm).
After enough rest (at least 10-15 minutes), blood pressure was acquired by a digital barometer (BC 08, Beurer, Germany) in a sitting position, and the mean of two estimations recorded for each person.
Biochemical assessments
Initial, a 10 mL venous blood sample was gotten from each subject following 7-10 hours of fasting, at that point centrifuged for 20 minutes. Fasting blood glucose (FBG) was measured using a commercial kit (Pars Azmoon, Tehran) by enzymatic colorimetric test (glucose oxidase). High-density lipoprotein (HDL-C) was assessed by the cholesterol oxidase phenol-amino-pyrine technique, and triglyceride was measured by the enzymatic method of glycerol-3-phosphate oxidase phenol-amino-pyrene with automatic apparatus (Selecta E, Vitalab, Netherland).
Dietary assessment and calculation of nutrient adequacy
Usual dietary intake was estimated using a valid and reliable 168-item Food Frequency Questionnaire (FFQ) (12) which involves a list of groceries and a standard size of each food item and was asked by trained dietitians via face-to-face interviews. Converting of consumed food portion sizes to grams was done by household measures (13) and calculated using an adjusted version of NUTRITIONIST IV software for Iranian foods (version 7.0; N-Squared Computing, Salem, OR, USA). Nutrient adequacy ratio (NAR), which is a measure of the adequacy of nutrient by comparing an individual’s daily intake of a nutrient with the recommended dietary intake (RDI) or recommended dietary allowance (RDA) for that nutrient (14) was used to calculate for the micronutrient adequacy for each individual. The mean adequacy ratio (MAR) is calculated as the average of the NAR values for the selected nutrients for a certain individual (14). The MAR was therefore derived by summing the NARs and dividing by the number of micronutrients assessed. A total of 10 vitamins (A, B1, B2, B3, B6, B9, B12, C, D, and E) and 6 minerals (calcium, iron, magnesium, phosphorus, selenium, and zinc) were involved in this study.
MetS definition
The presence of at least 3 of the accompanying criteria was considered as MetS: (1) central obesity (WC≥102 cm for men and ≥88cm for women); (2) low concentrations of HDL-C (<50 mg/dL for women and <40 mg/dL for men); (3) high serum TG levels (≥150 mg/dL); (4) abnormal homeostasis of glucose (FBG > 100 mg/dL); and (5) increased blood pressure (systolic blood pressure ≥130 mm Hg or diastolic blood pressure ≥85 mm Hg)(15).
Data analysis
All statistical analyses were done using the Statistical Package for the Social Sciences (SPSS version 25; SPSS Inc.). We considered p<0.05 as the significance level. The normality test was performed by the Kolmogorov-Smirnov test and also the Q-Q plot. We analyzed the study participants’ characteristics according to nutrient adequacy quartiles, using one-way analysis of variance (ANOVA) and χ2 tests for continuous and categorical variables, respectively. Data are shown as the mean ± SD for continuous variables and percent (%) for categorical ones. In the next step, for the modeling of relationships, a linear regression test was conducted to assess the association of metabolic syndrome components with energy-adjusted nutrient adequacy after controlling for confounders such as age, sex, total physical activity, smoking habits, educational level, BMI, marital status, and occupation. Odds ratio and 95% confidence intervals were obtained using logistic regression to determine the relationship of the energy-adjusted nutrient adequacy with MetS. The risk was reported in crude and 2 adjusted models. In this analysis, the first quartile of exposure was considered as the reference category.