Study design and participants
This study was conducted in the framework of the TLGS. The TLGS includes two major junctures: The first juncture was the 1st phase, a cross-sectional study designed to determine the prevalence of non-communicable diseases (NCDs) risk factors executed from 1999 to 2001. A total of 15005 individuals aged ≥three who were residents of district 13 of Tehran were recruited in the study. The second juncture includes five follow-up phases that have been implemented from 2002 to 2019 every three years. More study details have been reported previously (29).
In the current study, from all the individuals who participated in the TLGS during the 2016-2019 (6th phase), 2728 participants aged ≥20 years with complete data on depression, anxiety, and stress were recruited. 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
MetS and Type 2 diabetes: MetS was defined as having any three of the following abnormalities: 1) ethnic-based abdominal obesity, which described as waist circumference ≥ 90 cm for men and women (30); 2) HDL-cholesterol < 40 mg/dl in men or 50 mg/dl in women; 3) triglyceride ≥ 150 mg/dl; 4) Fasting blood sugar (FBS) ≥ 126 mg/dl or known treatment for diabetes; 5) blood pressure ≥ 130/85 mmHg or use of antihypertensive drugs (31). Type 2 diabetes was defined as FBS ≥ 126 mg/dl or taking medication for diagnosed diabetes. Obesity was defined as BMI≥30 kg/m².
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 the Joint Interim Statement (JIS) and the American Diabetes Association (ADA), respectively.
Sociodemographic characteristics: The participants' age, sex, marital status, job status, and educational level were assessed via a pretest questionnaire. Participants' educational level was 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). The frequency and duration of each leisure-time and work physical activity (standing, housework, and work activities more intense than standing) were calculated as hour/week. Then they were multiplied by the weight and the metabolic equivalent task (MET) of the particular act to calculate the energy expenditure for each domain. Total physical activity was calculated by adding each domain's energy expenditure and was categorized into three groups of low (<600), moderate (600-3000), and high (≥3000) physical activity (32).
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 analyzed using an electronic digital scale that its accuracy was up to 100 g. The height was examined in cm, while participants were standing normally using a tape meter stadiometer. Waist circumference was measured via an unstretched measuring tape and recorded to the nearest 0.1 cm. 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 samples 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 (33).
Depression, anxiety, and stress: The Persian version of depression, anxiety, and stress scale-21 items (DASS-21) was used to assess emotional distress among 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 (34). DASS-21 is a self-report questionnaire, including three scales, and each scale was composed of seven items divided into subscales with similar content. Examples of items in each subscale are "I couldn't seem to experience any positive feeling at all" for depression; "I experienced trembling (e.g., in the hands)" for anxiety; and "I felt that I was using a lot of nervous energy" for stress. 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). Depression, anxiety, and stress were treated as ordinal variables in the current study. 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. According to the DASS-21 scoring structure, each scale in this questionnaire multiplied by two, so the highest score for each scale was 42 (35).
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 phenotypes were compared via the one-way ANOVA and Chi-square test, respectively. To show an overview and a general comparison, 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 across obesity phenotypes and ordinal outcomes of depression, anxiety, and stress. Sex-specific odds ratios (ORs) of higher depression, anxiety, and stress in different obesity phenotypes 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 0.05 was considered statistically significant. Statistical analysis was conducted using the IBM SPSS 24 (SPSS Inc., Chicago, IL, USA).