Background: Insomnia is one of the most prevalent health concerns and has a major impact on human health and quality of life. Increasing evidence indicates the gut microbiota’s role in sleep regulation through the gut–brain axis. This systematic review aims to summarise current evidence on the role of gut microbiota alterations in insomnia. Methods: We searched PubMed, Embase, and Cochrane Library through November 2024 for case–control studies comparing gut microbiota in insomnia subjects and controls. The primary outcome was changes in microbiota diversity and bacteria taxonomy. Results: We included 15 case–control studies from 14 articles, consisting of 1321 subjects (603 insomnia; 718 controls). Eight studies showed reduced alpha diversity and eleven showed altered beta diversity in insomnia subjects. Depletions of specific taxa such as Lactobacillales (class Bacilli), Faecalibacterium, and Lachnospira and the enrichment of Actinobacteria, Bacteroidales (class Bacteroidia), and several genera, including Streptococcus, Blautia, Lactobacillus, Clostridium, Holdemanella, and Eubacterium hallii, were observed in insomnia subjects. There was a negative association between insomnia severity and abundance of Faecalibacterium and Lachnospira, and positive associations with Blautia. Conclusions: This systematic review identifies specific alterations in gut microbiota among insomnia subjects characterised by taxonomic changes that may serve as promising therapeutic targets for sleep disorders.

Insomnia poses considerable risks to both physical and mental health, leading to cognitive impairment, weakened immune function, metabolic dysfunction, cardiovascular issues, and reduced quality of life. Given the significant global increase in insomnia and the growing scientific evidence connecting gut microbiota to this disorder, targeting gut microbiota as an intervention for insomnia has gained popularity. In this review, we summarize current microbiome-based therapeutics for insomnia, including dietary modifications; probiotic, prebiotic, postbiotic, and synbiotic interventions; and fecal microbiota transplantation. Moreover, we assess the capabilities and weaknesses of these technologies to offer valuable insights for future studies.

Autism spectrum disorder (ASD) frequently co-occurs with malnutrition and gut dysbiosis, yet the underlying mechanisms remain poorly understood. Herein, this cross-sectional study first profiles dietary intake differences using dietary records from 210,874 participants (ASD = 232; non-ASD = 210,642; median age = 56.18) from the UK Biobank (UKB). Second, a bi-directional Mendelian Randomization (MR) approach serves to dissect relationships between ASD genetic susceptibility and dietary preferences by leveraging genome-wide association metadata from the iPSYCH-PGC (ASD) and UKB (dietary intake/food-liking traits). The same strategy is implemented to identify ASD-associated gut microbial species. Mediation analyses further assess the role of gut microbiota in the association between ASD and dietary preferences. Subjects with ASD exhibit higher consumption of cheese, processed meat, and oily fish, alongside lower intake of fruits, and demonstrate a preference for high-fat/salt and energy-dense foods. Additionally, the depletion of Turicibacter, Streptococcus, and Lachnospiraceae NK4A136 was causally related with ASD (all false discovery rate < 0.05; β = −0.15, β = −0.10, β = −0.093, respectively), which significantly mediates the ASD-associated elevated preference for high-fat/salt foods. In conclusion, ASD is associated with specific dietary preferences, likely mediated via gut microbiota, highlighting the future potential of gut microbiome-based therapeutics to modify eating disorders for ASD.