Study Design and Participants
The current cross-sectional study was conducted among overweight and obese women who attended health centers in Tehran, Iran, in 2018. A random sample of 280 women was selected from 20 various health centers by a multistage cluster random sampling method. Eligible criteria included body mass index in the range of 25-40 kg/m2. Exclusion criteria included: history of cardiovascular disease, hypertension, diabetes mellitus, hepatic or renal disease, alcohol usage, medicine usage other than birth control pills, pregnancy or lactation, following a specific diet or body weight fluctuation over the past 1 year. Informed consent was obtained from all participants. This study was approved by the research council (research project number: 95-03-161-33142, 95-04-161-33893) and ethics committee (research ethics number: IR.TUMS.VCR.REC.1395.1597).
Dietary Assessment
Participants’ dietary intake over the past year was assessed using a valid and reliable semi-quantitative food frequency questionnaire (FFQ). This FFQ consists of 147 food items with standard serving sizes, and participants were asked to specify their consumption frequency for each food item on a daily, weekly, monthly or yearly basis. Then, nutrient and energy intakes were computed using NUTRITIONIST IV software (version 7.0; N-Squared Computing, Salem, OR), which was tailored for Iranian foods. For calculating EDII, all nutrient values were adjusted for energy intake using the residual method.
Dietary Inflammatory Index Calculation
To calculate EDII for the participants of this study, the dietary data were first linked to the regionally representative world database, which provided a robust estimate of a mean and standard deviation for each parameter. These then become the multipliers to express an individual’s exposure relative to the ‘standard global mean’ as a z-score. A z-score for each food consumed was calculated by subtracting the ‘standard mean’ from the actual food parameter value, and divided by its standard deviation. Next, to minimize the effect of ‘right skewing’, this value was then converted to a centered percentile score, which was then multiplied by the respective food parameter inflammatory effect score to obtain the subject’s food parameter-specific EDII score. All of the food-parameter-specific EDII scores were then summed together to create an overall EDII score for every subject in the study [18]. In total, the EDII computed based on this study’s FFQ includes data on 29 of the 45 possible food variables composing the EDII: energy, carbohydrate, protein, fat, fiber, cholesterol, trans fat, SFAs, MUFAs, PUFAs, omega-3, omega-6, niacin, thiamin, riboflavin, vitamin B-6, vitamin B-12, iron, magnesium, selenium, zinc, vitamin A, vitamin C, vitamin D, vitamin E, folic acid, b-carotene, caffeine, onion and tea.
Quality of Life Assessment
The SF-36 is a short-form, self-administered quality of life scoring questionnaire. It consists of 36 questions, 35 of which are compressed into eight multi-item scales including: physical functioning (PF), role-physical (RP), bodily pain (BP), general health (GH), vitality (VT), social functioning (SF), role emotional (RE), and mental health (MH). (1) Physical Functioning (PF) is a 10-question scale that captures abilities to deal with the physical requirement of life, such as attending to personal needs, walking, and flexibility. (2) Role-Physical (RP) is a four-item scale that evaluates the extent to which physical capabilities limit activity. (3) Bodily Pain (BP) is a two-item scale that evaluates the perceived amount of pain experienced during the most recent 4 weeks and the extent to which that pain interfered with normal work activities. (4) General Health (GH) is a five-item scale that evaluates general health in terms of personal perception. (5) Vitality (VT) is a four-item scale that evaluates feeling of pep, energy, and fatigue. (6) Social Functioning (SF) is a two item scale that evaluates the extent and amount of time, if any, that physical health or emotional problems interfered with family, friends, and other social interactions during the most recent 4 weeks. (7) Role-Emotional (RE) is a three item scale that evaluates the extent, if any, to which emotional factors interfere with work or other activities. (8) Mental Health (MH) is a five-item scale that evaluates feelings principally of anxiety and depression [19, 20]. The SF-36 also includes a question self-evaluating health changes in the past year (reported health), which does not belong to the eight dimensions, or the total SF-36 score. Each of these 8 dimensions has a score between 0 (worst health) to 100 (best health). [21-23]
Biochemical Assessment:
Blood samples were collected early in the morning after 12-hour overnight fasting. Serum was separated from whole blood samples and stored at −80 °C until the assay Serum hs-CRP levels was measured by an immunoturbidimetric assay with a Pars Azmoon kit (Pars Azmoon Inc. Tehran, Iran).
Anthropometric Assessment:
Anthropometric measures, including body weight, body mass index, waist circumferences and waist-hip ratio, were measured in an overnight fasting state, without shoes, with minimal clothing and by the use of a multi-frequency bioelectrical impedance analyzer In-body 770 scanner (In-body Co., Seoul, Korea). Height was measured with a Seca 206 scale, based on standard protocol.
Assessment of Other Variables:
Physical activity status and socio-demographic information was obtained by questionnaire. Data on physical activity was gathered using the IPAQ questionnaire. Activity was classified as light, medium or heavy levels (IPAQ). The metabolic equation hours per day score (MET-min/week) was then calculated for each subject [24, 25].
Statistical Analyses:
The EDII was analyzed as a dichotomous variable, categorized based on the median value of the EDII (0.05). EDII (as dichotomous) was examined across the following characteristics: age, weight, height, economic status, BMI, waist circumference, waist-hip ratio, energy intake, physical activity, and quality of life measurements, via independent sample T-test analyses. Comparisons of different food group intakes across the EDII quartiles were analyzed through an independent sample T-test. Multivariable linear regression analyses of the continuous EDII score were conducted to determine the association of the EDII with quality of life and hs-CRP levels. Variables were adjusted for the following confounding factors: age, weight, physical activity, smoking, economic status and employment status. The results are reported as percentage change (β) with 95% confidence intervals (95% CI). Statistical analysis was performed using SPSS (version 21) (SPSS Inc., Chicago, USA). Significance was set at a probability of ≤0.05 for all tests.