Jun Nishihira

The inflammatory potential of the diet, as measured by the Dietary Inflammatory Index (DII®), has been repeatedly shown to be associated with various inflammatory markers and mental and physical health outcomes. Of specific importance, several cross-sectional studies revealed mixed results regarding the correlations between the DII and sleep outcomes. Hence, in the current paper, a systematic review that examines the associations between the DII, sleep duration, and sleep quality was performed. The PubMed database was systematically searched for studies published up to November 2023 following PRISMA guidelines. Only cross-sectional studies that assessed the DII, sleep duration, and sleep quality across healthy and unhealthy cohorts were included. Eleven and seven studies were included in the systematic review for sleep quality and duration, respectively. The results of the present systematic review show that pro-inflammatory diets may be associated with poor sleep outcomes (duration and quality); however, as the current literature is inconsistent and limited, further cross-sectional studies in larger cohorts are necessary to (i) explore this relationship to address this heterogeneity and (ii) explore populations that are more sensitive to diet-induced inflammation.

Human gut health is closely related to sleep. We aimed to evaluate the efficacy of yeast mannan (YM) in improving bowel habits and sleep quality, along with metabolomics in fecal samples. A total of 40 healthy adults (age range, 22–64 years) with discomfort in defecation were enrolled and randomly allocated to receive either YM (n = 20; 1.1 g/day) or placebo (n = 20) for four weeks. Participants recorded their defecation habits throughout the test periods. Sleep electroencephalogram (EEG) recording using an EEG device and fecal sampling were performed pre- and post-treatment. The YM group significantly increased defecation frequency and stool volumes compared to the placebo group. After 4 weeks of treatment, the non-REM sleep stage 3 (N3) duration in the YM group was significantly higher than that in the placebo group. YM ingestion significantly lengthened total time in bed (TIB) and significantly shortened N3 latency compared to placebo intake during the trial. The metabolomics analysis found a total of 20 metabolite differences between the YM and placebo groups. As a result of stepwise linear regression, changes in fecal propionate and gamma-aminobutyric acid (GABA) levels were identified as the primary factors explaining changes in TIB and N3 latency, respectively. Our findings suggest that the prebiotic YM could be beneficial to gut health and sleep quality.