This cross-sectional study was designed to investigate the association of dietary inflammatory index, anthropometric and body composition indices with depression and anxiety in Iranian adolescent girls in 2021.
After adjusting for confounding variables, there was no significant relationship between DII with anxiety and depression. In line with our study, a cross-sectional study indicated that there was no relationship between DII and anxiety in either males or females (26). Also, a recent cross-sectional study was conducted by Mohammadi et al. 2022 indicated the same result to our study (27). Furthermore, a cross-sectional study included 364 female adolescents selected from high schools in the five regions of Tabriz, Iran, after adjusting for confounder variables, indicated that there was no association between DII and anxiety (16). Although, a previous study suggested that a higher DII score was associated with anxiety in 2047 adults with both sexes (28). Bigger sample size in previous study and differences in mean age of participants may be a reason for this discrepancy with our study. Additionally, similar to our study, a study indicated that there was no association between DII and depression (16) whereas, in contrast with our study, a recent study was published by Luo et al., demonstrated that diets with higher dietary inflammation potential can increases the risk of depression in 10951 adults (29). Higher mean age of participants in Luo et al., study may be a reason for this discrepancy with our results. Sample size of our study was very lower than previous study. Furthermore, both genders participated in previous study, while adolescent girls were participated in this study and these differences can effect on final results. In a previous cross-sectional study indicated that association between higher DII and more odds of depression symptoms in males compare to females (30). In addition, in a cross-sectional study from NHANES 2007–2018, a J-shaped association between DII and depression was found in adults from the United States (31). Another study was designed to investigate the relationship between DII and depression among female students of nutrition and dietetics department, whom they be assumed to be conscious about health (32). The 3-day dietary records and Beck Depression Inventory were used to assess DII and depression status of the students. A positive association was found between DII and depression in their study. Possible causes of conflict result to our study are differences in used questionnaires and, also nutrition students have more information about diet and this may be an important factor in contrary results.
Also, a positive association was seen among anthropometric measurements, depression and anxiety in current study. A study was conducted by Moussavi et al. in 2020 indicated that there was a positive association between anthropometric measurements and depression, but not anxiety (33). Possible reasons for discrepancy in association between anthropometric measurements and anxiety with our study, are they conducted their study on 157 adult females and males, which used a smaller sample size and different population than current study. Furthermore, another study suggested a positive correlation between the sum scores of the depression scales and the waist/hip ratio or the sagittal abdominal diameter of males and our study is in line with their finding (34). Although, according to our search, limited study was found to assess the association among anthropometric measurements, depression and anxiety, so further studies are needed to clarify this finding.
After adjusting multiple confounder, there was a significant positive association between the DII, anthropometric and body composition. In line with our study, Ruiz- Canela M et al. found a direct association between DII and obesity (35). They concluded that diet has a key role in the development of obesity through inflammatory modulation mechanism. Apart from that, in a prospective cohort study, Ramallah et al. reported that the DII was significantly associated with weight gain and a higher risk of developing overweight or obesity (36). Another finding is consistent with the finding of our study, Alam et al. confirmed that there is a positive correlation between the DII and obesity, which supports their hypothesis that diet may have a role in the development of obesity in the elderly (37). Similar to the study of Labonte et al. (38), after adjusting multiple factors, they did not observe a significant association between the DII and odds of being overweight. In contrast to our study, Correa-Rodríguez et al. reported that the DII was associated with obesity-related parameters such as fat-free mass and weight, but not with BMI and fat mass in adults (39). It can be due to difference in the age of the participants and adjusted factors. It seems that DII may be more effective on obesity-related traits during childhood and adolescence. A recent cross-sectional study included 361 college students, indicated that there was no association between the DII and obesity indices (40). The impact of confounding factors, the number of dietary parameters used to compute the DII score, and different food intake data collection methods can be reasons of discrepancies in the previous finding from this study.
Previous studies have suggested possible mechanisms which overweight and obesity is related to a low-grade inflammation resulting from chronic activation of the innate immune system, which can subsequently lead to insulin resistance and impaired glucose tolerance (41). There is a reverse causation effect between inflammation and obesity, inflammation is often assumed as a result of the obesity, while, new studies recommend that inflammation may be a reason of obesity development (42). For example, knockout animal studies have shown that some pro-inflammatory cytokines, including IL-6 and TNF-α, is associated with the development of obesity (43, 44). Also, in a study was conducted on adolescents have shown that CRP levels were significantly associated with overweight and obesity in both boys and girls. They suggest that during adolescence, overweight and obesity is associated with a chronic low-grade inflammatory response (45). In addition, some studies in older adults have shown that increasing levels of inflammatory markers, including inflammation-sensitive proteins such as IL-6, CRP, factor VIIIc, white blood cell count, and platelet count, were related to a higher risk of future obesity (46–48).
Consumption of higher inflammatory potential with higher proportion of fat can activate pro-inflammatory pathways, and is associated with oxidative stress that leads into systemic inflammation (49). While, consumption of fruits and vegetables by its anti-oxidative capacity can modulate oxidative stress and inflammation (50, 51). Totally, studies indicated that anti-inflammatory diet leads to a less level of clinical inflammatory markers, including IL-6 and CRP (52–54). In addition, short chain fatty acids are products of gut microbiota when the plant-based diet and diets with a lower DII score is consumed and have anti-inflammatory properties and reduced inflammatory markers (52, 55, 56).Altogether, this may clarify how adherence to diets with anti-inflammatory property, which are characterized by an increased intake of fruits and vegetables, wholegrains, pulses/legumes and nuts can decrease the risk of obesity.
To the best of the authors’ knowledge, this is one of the first studies that has examined the association between DII, anxiety, depression and anthropometric incidence in Iranian adolescent girls. Although, the results of this study should be interpreted with caution because of the following limitations. First, because of the hormonal changes in adolescent girls can cause change in blood inflammatory indices which may affect results of the present study. Second, dietary assessments that are subject to recall biases which could be an important limitation. To minimize this bias, the questionnaires were filled out by a trained nutritionist for all participants. Also, adolescents’ responses were further checked by mothers to ensure their reliability. The use of valid and reliable FFQ can help in minimizing the recall bias. Third, this study did not measure the blood inflammatory indicators and association between these indicators with the DII. Finally, another consideration to take into account when interpreting the results is small sample size in present study, which future studies are needed to be performed to resolve these problems.