This study investigated the association between various metabolic indicators and weight status (healthy, NWO, and OW/O). The results suggested that the female healthy individuals had higher levels of HDL, while male NWO participants had increased ALT levels. In addition, OW/O was associated with increased SBP and DBP.
According to the literature, the associations between NWO and metabolic disturbances have been evaluated in various studies (9, 20-22). A study on the US population indicated that the NWO individuals aged above 20 years were four times more prone to metabolic syndrome compared to those with normal body fat and BMI (6). Similarly, the prevalence of metabolic syndrome was four folds higher in NWO individuals in an Iranian adult population (23). It should be explained that high or abnormal adiposity, especially visceral fat, is related to insulin resistance which is a key factor in the development of metabolic syndrome. Additionally, dysfunctional adipose tissues produce pro-inflammatory cytokines instigating systemic inflammation which is associated with cardiometabolic risk and chronic diseases (24).
Although the present study revealed no significant difference among the study groups regarding the FBS level and lipid profile components, the results of a previous study showed that NWO women had higher lipid levels, dyslipidemia, blood pressure, and fasting hyperglycemia compared to lean women (22). Another study on Asian Indians also demonstrated that NWO participants had increased levels of LDL and TG compared to those with overt obesity. Additionally, the odds ratio of dyslipidemia (OR: 2.37, [95% CI: 1.55, 3.64]) and diabetes (OR: 2.72, [95% CI:1.46, 5.08]) was remarkably higher in NWO individuals (25). In line with these findings, Ito et al. disclosed that dyslipidemia was related to excess accumulation of fat mass, especially central obesity, in NWO individuals (26). Although NWO individuals do not always manifest metabolic abnormalities, they are almost the same as individuals with preobesity/obesity concerning the exposure to cardiovascular risk factors (27).
The current study findings revealed significantly increased levels of ALT in the NWO group in comparison with the two other groups. These findings were in agreement with a previous study on US residents which supported the effect of central adiposity, regardless of BMI status, in the prediction of liver enzymes increment (28). On the other hand, Marques-Vidal showed no significant differences between the lean and NWO women regarding liver enzymes including ALT, AST, and GGT (22). Importantly, a longitudinal study performed on adolescent girls demonstrated that instead of the total adipose tissue, the proportion of visceral adipose tissue to subcutaneous adipose tissue (VAT / SAT) better predicted intrahepatic fat accumulation (29). Nonetheless, a relationship has been suggested between hepatic impairment, partly diagnosed by elevated liver enzymes, and cardiometabolic disturbances such as low HDL levels, independent of obesity or adiposity (30).
The present study findings revealed significantly higher systolic and diastolic blood pressure among OW/O group. Similarly, a cross-sectional study on 1551 individuals aged 15 – 79 years showed that BMI, similar to body fat, was a good predictor of blood pressure (31). Akram et al. also reported that increase in weight was accompanied by an increase in the incidence of hypertension (32). It has been previously explained that abdominal adiposity increases free fatty acid levels, which causes hyperinsulinemia and insulin resistance. In addition, hyperinsulinemia is responsible for adrenergic activity enhancement and sodium retention, leading to high arterial blood pressure in individuals with obesity (33). Therefore, the relationship of OW/O with high blood pressure could be explained by these mechanisms.
One of the strengths of this study was using the data from a cohort study conducted on a large sample of adults. Additionally, adjustment was performed for several variables. Despite these strengths, this study had some limitations. A potential limitation of the study was related to its cross-sectional design, which made it impossible to obtain causal conclusions. Moreover, despite employing a valid and reliable FFQ to estimate the energy intake, measurement error might be a concern. Finally, medical university employees may have different physical activity status and health literacy than the general population of the city; therefore the results should not be generalized to the whole population.