Study design and participants
This study was conducted in the framework of the Tehran Lipid and Glucose Study (TLGS). The TLGS includes two major junctures: phase 1, a cross-sectional study designed to determine the prevalence of non-communicable diseases (NCDs) risk factors executed from 1999 to 2001, and five follow up re-exam have been implemented from 2002 to 2015. More study details have been reported previously (28).
Form all the individuals who participated in the TLGS during 2016-2018 (6th phase), 2728 participants were recruited aged ≥20 years with complete data on depression, anxiety, and stress. After excluding those with missing data on BMI, MetS components, or covariates (sociodemographic factors, smoking status, and level of physical activity) (n=259), the final data of 2469 adults (1158 men and 1311 women) were analyzed. This study was approved by the ethics committee of the Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences. All the participants signed the written informed consent before data collection.
Definition and measurements
Obesity phenotypes: The participants were categorized into four obesity phenotypes: 1) Metabolically healthy non-obese (MHNO), 2) Metabolically healthy obese (MHO) 3) Metabolically unhealthy non-obese (MUNO), and 4) Metabolically unhealthy obese (MUO). Metabolically unhealthy status was defined as having MetS or diabetes type 2 according to Joint Interim Statement (JIS) and American Diabetes Association (ADA) respectively. MetS was defined as having any three of the following abnormalities: 1) ethnic-based abdominal obesity which described as waist circumference ≥ 90 for men and women (29) ; 2) HDL-cholesterol < 40 mg/dl in men or 50 mg/dl in women; 3) triglyceride ≥ 150 mg/dl; 4) glucose FPG≥ 100 mg/dl or known treatment for diabetes; 5) blood pressure ≥ 130/85 mmHg or use of antihypertensive drugs (30).
Type 2 diabetes was defined as fasting blood sugar ≥ 126 mg/dl or 2-hour post-load glucose ≥ 200 mg/dl or taking medication for diagnosed diabetes. Obesity was defined as BMI≥30 kg/m².
Sociodemographic characteristics: The participants' age, gender, marital status, job status, and educational level were assessed via a pretest questionnaire. The educational level of participants defined as 1) Primary: including people with less than a high school diploma; 2) Secondary: including people with a high school diploma; and 3) Higher: including people with a college degree or higher.
Smoking and physical activity status: The smoking habit of participants was classified into two groups: 1) smokers (daily and occasionally smokers) and 2) non-smokers (ex-smokers or never smokers). Physical activity levels were evaluated by the validated Iranian version of the Modifiable Activity Questionnaire (MAQ). To calculate the energy expenditure for activates of sport, job, and travel during one week, the metabolic equivalent task (MET) of the particular act was multiplied by a weight and the sum of all acts considered as total energy expenditure in adults. After calculating total MET-value for adults, it was categorized into three groups of low (<600), moderate (600-3000), and high (≥3000) physical activity (31).
Clinical and anthropometric measurements: Trained personnel measured weight, height, and waist circumferences of participants while they wore light clothes and were barefoot. The weight was analzyed using an electronic digital scale that its accuracy was up to 100 g. The height was examined while participants were standing in a normal position. Waist circumference was measured via an unstretched measuring tape and recorded to the nearest 0.1. The blood pressure was measured after a 15-minute rest period in the seated position twice by qualified physicians via a standard mercury sphygmomanometer; the average of two measurements was considered for analysis.
Biochemical measurements: The blood sample was taken from the participants after a 12-14 hour overnight fast by trained personnel in the data collection center of the TLGS. All blood sample of fasting blood sugar (FBS) and serum lipids (total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG)) were analyzed in the TLGS research laboratory on the same day. Additional information has been previously published about the biochemical measurements (32).
Depression, anxiety, and stress: The Persian version of depression, anxiety, and stress scale-21 items (DASS-21) was used to assess the emotional distress of participants. The psychometric properties of the Persian version of DASS-21 have been previously studied among the Iranian population, and its reliability and validity were approved (33) . DASS-21 is a self-report questionnaire, including three scales, and each scale was composed of seven items divided into subscales with similar content. The participants completed this questionnaire by rating each item to reflect their emotional experiences from 0 (did not apply to me at all) to 3 (applied to me very much). The cut-off scores for conventional severity labels were used as follows: 1) Depression: normal: 0-9, mild: 10-13, moderate: 14-20, and severe: +21; 2) Anxiety: normal: 0-7, mild: 8-9, moderate: 10-14, and severe: +15; 3) Stress: normal: 0-14, mild: 15-18, moderate: 19-25, and severe: +26. The highest score for each scale was 42, multiplied by 2 (34).
Statistical analysis
Continuous variables were expressed as mean ± standard deviation (SD), and categorical variables were expressed as frequency (percentage). The continuous and categorical variables among different obesity and MetS groups were cmpared via one way ANOVA and Chi-square test, respectively. Mean scores of depression, anxiety, and stress were compared across different obesity phenotypes via the analysis of covariance and age, marital status, education, job status, smoking status, and level of physical activity were considered as adjustments. Ordinal logistic regression was used to explore the associations between obesity/MetS groups and ordinal outcomes of depression, anxiety, and stress. Sex-specific ORs with 95% confidence intervals were calculated and reported for men and women separately; model 1 was unadjusted, while model 2 was adjusted for age, marital status (Ref.: Married), education (Ref.: Higher), job status (Ref.: Employed), smoking status (Ref.: Non-smoker), and level of physical activity (Ref: High). All tests were two-sided, and a p-value of less than 5% was considered statistically significant. Statistical analysis was conducted using the IBM SPSS 24 (SPSS Inc., Chicago, IL, USA).