In the present study, we were able to show that the dietary ORAC index was higher in normal weight volunteers as compared to the overweight/obese group. In addition, there was an inverse relationship between the dietary ORAC index and anthropometric indices, FBG, TG, TC and LDL. To the best of our knowledge, this is the first study investigating the association between dietary ORAC index, body composition and plasma biochemical markers in both overweight/obese and normal weight groups. Previous studies have shown an inverse relationship between the consumption of dietary antioxidants and several outcomes such as stroke , hypertension , myocardial infarction , cancer  and mortality .
In the present study, the dietary ORAC index was inversely correlated with BMI. Excessive fat accumulation can lead to obesity . With increased obesity, the extra stored fat increases the production of oxygen radicals and inflammatory factors, as well as cholesterol and blood lipids . Excess calories inhibit the production of adiponectin . In the short time, the body tries to modify these damaging anomalies, but in the long run the immune system’s ability to function is attenuated and oxidative stress can damage cells. Additionally, increased secretion of leptin usually accompanied by obesity leads to activation of T-lymphocytes leading to the production of proinflammatory factors, such as interleukin–2 and TNF-α which in turn can cause inflammation and oxidative stress in the body . The body responds to these changes by using natural antioxidants, such as vitamins E and C. If the body is unable to eliminate these factors, excessive accumulation of oxidants can lead to impaired protein and fat function, cellular dysfunction and, ultimately, to inflammation [5,33,34]. Obesity-induced inflammation and oxidative stress increase insulin resistance by reducing the expression of insulin receptor substrate–1 (IRS–1) . As a result, promoting the body’s antioxidant capacity can greatly prevent the complications of diabetes .
Consuming antioxidant-rich foods with a high capacity to absorb oxygen radicals will give the immune system a chance to counteract inflammation.Despitethe type of the present study as a short study, similar to the findings in the current study, the higher dietary ORAC index has been an indication of higher quality of the diet and was related to higher consumption of fruits and vegetables. The favorable effects of these antioxidant-rich foods on improvement of fasting blood glucose, lipid profile and obesity have been investigated in some pre-clinical and clinical studies[38–42]. In recent years, chemical antioxidants, such as “phytochemicals”, are suggested as plausible candidates in the prevention and/or treatment of specific diseases, including obesity and obesity-related metabolic disorders .
Parallel with our findings, many studies have shown that the dietary antioxidant capacity of volunteers with normal weight is higher as compared to overweight/obese ones. In a study, Hermsdorff et al demonstrated that dietary antioxidant capacity was negatively and significantly correlated with waist circumference (WC) . Also another study showed that high WHR is linked with increased oxidative stress . Similarly, an increase in dietary antioxidant was shown to reduce the incidence of abdominal obesity . In line with our findings, previous studies showed that obesity is related with unhealthy diet, which is full of carbohydrate, fat, simple sugars and sweet beverages, whereas a protective effect against obesity is observed in the consumption of a diet rich in fruits and vegetables [46,47] and a diet high in vegetables and fruits has been positively related to the consumption of antioxidant vitamins .
The present study showed that there was an inverse association between the dietary ORAC index with FBG, TG, LDL and TC, whereas a positive correlation between ORAC and HDL was observed. As well as, Many studies have supported these findings [48–50]. Some studies have also reported that antioxidant capacity in obese and overweight volunteers is promoted which was postulated to be due to immune system’s trying to override the present inflammation [51,52].