Discussion
In the present study, the Association of DII score with obesity indexes and sleep quality was assessed in Iranian female college students which indicated no significant association between DII score and obesity. However, a significant association was observed between the DII and PSQI score.
Consistent with our findings, the study by Sen et al. did not show any significant associations between DII and obesity (OR=1.4, 95% CI -0.8-2.3, p=0.23).42 Moreover, the findings from the SU.VI.MAX study with 3726 participants indicated no significant association between WC and DII score (p=0.45).43 In another cross-sectional survey among the Luxembourg population (ORISCAV-LUX), no significant associations was observed in the Association between DII score and WC, which was in line with our findings.44 Moreover, a cross-sectional study among 464 police officers indicated that DII has no association with WC as a Mets component.45 Sokol et al. showed a significant association of DII with waist components only in males, not in females.46 In contrast to our findings, in some other research studies that were carried out in Iran,47 and Spain (PREDIMED’ study and SUN cohort study),48,49 a significant association between DII and obesity or Mets components were detected. Lack of significant Association of the DII score with WC and BMI in the present study may be related to the sample size, type of research (cross-sectional), the numbers of food items in the calculation of DII and a small mean of BMI compared to studies that have observed a significant association. In the present study, a significant association was observed between the DII and PSQI score. In the recent study by Lopez et al., it was shown that the DII score was only positively associated with daytime sleepiness as a component of PSQI (β=0.47, p value<0.05).50 In the study by Godos et al. participants in the highest quartile of DII score were more likely to have a poor sleep (OR = 0.49, 95% CI: 0.31- 0.78). Moreover, the authors demonstrated that high adherence to the Mediterranean diet as an anti-inflammatory dietary pattern, could improve sleep quality in Italian adults through the direct and indirect effects on health and body weight status, respectively.51 Bilgic et al. showed that increased malnutrition-inflammation score was significantly associated with the presence of depression, sleep disorders, and poor quality of life52.
The evidence from studies represented that that poor sleep was associated with chronic, low-grade inflammation status. Short and long sleep duration was associated with increased inflammation markers, and sleep disruption may be related to diabetes via a mechanism of low-grade systemic inflammation53. Several studies suggested that a decrease in the number of hypocretin-containing neurons may be caused by an inflammatory- or immune-mediated process54-56. Hypocretin cell loss was observed in most patients with sleep disorder narcolepsy54.
Gordon‑Dseagu et al. examined the Association between sleep variables and 891 fasting plasma metabolites among the participants from the Dietary Approaches to Stop Hypertension (DASH) trial. They observed that sleep parameters was associated with metabolites and pathways which had a relationship with inflammation and oxidative stress, including erythrulose (advanced glycation end-product) (positive Association) and several γ-glutamyl pathway metabolites, including CMPF (fatty acid, dicarboxylate), isovalerate (valine, leucine and isoleucine and fatty acid metabolism) and HWESASXX (polypeptide) (inverse association).57 The mechanisms about the Association between the DII score and health may be linked to the primary role of several dietary components on systemic inflammatory pathways and gut microbiota.58,59 It has been shown that low intake of vegetables and unhealthy eating habits were associated with poor sleep quality; vegetables are important sources of vitamins and polyphenols, which can lead to reduce pro-inflammatory response and oxidative damage, and represent neuroprotective effects.60 Omega 3 fatty acids and MUFA have known as anti-inflammatory properties. It was found in some studies regarding both Docosahexaenoic acid and the Docosahexaenoic acid: Arachidonic acid ratio affected sleep quality and inflammation61. In contrast, high intake of meat products and refined carbohydrates have been related to an increase in pro-inflammatory response.60 Regarding the influence of the gut microbiota on inflammation, it could be stated that there was a large data of various studies suggesting a mechanistic link between gut-derived inflammatory response and neurodegeneration via the pathways including modulation of plasma levels of lipopolysaccharide, the inflammasome, type I interferon, and nuclear factor kappa B cells (NF-KB).62 It should be noted that the present study’s participants had less intake of foods impacting the availability of tryptophan, and its conversion to serotonin and melatonin such as protein and vitamins B group compared to global mean intake.63