BACKGROUND Many diverse inflammatory pathophysiologic mechanisms have been linked to mental disorders, and through the past decade an increasing interest in the gut microbiota and its relation to mental health has been arising. We aimed to systematically review studies of alterations in gut microbiota of patients suffering from psychotic disorders, bipolar disorder or depression compared to healthy controls. METHODS We systematically searched the databases CENTRAL, PubMed, EMBASE, PsycINFO and LILACS. Primary outcome was to compare the gut microbiota of patients suffering from psychotic disorders, bipolar disorder or depression with healthy controls. RESULTS We identified 17 studies, covering 744 patients and 620 healthy controls. The most consistent microbiota changes were a tendency towards higher abundance of Actinobacteria and lower abundance of Firmicutes at the phylum level, lower abundance of Lachnospiraceae at family level and lower abundance of Faecalibacterium at genus level for the mental disorders overall. However, we found that all studies had risk of bias and that the included studies displayed great variability in methods of storage, analysis of the fecal samples, reporting of results and statistics used. CONCLUSION Due to the many limitations of the included studies the findings should be interpreted with caution. Larger studies (especially of schizophrenia and major depressive disorder) are needed, but it is also of great importance to gather information of and control for factors that influence the result of a microbiota analysis including body mass index (BMI), smoking, alcohol consumption, diet habits, antibiotics, sample handling, wet laboratory methods and statistics.

中文翻译：

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精神病和情感障碍患者肠道微生物变化：系统评价

背景许多不同的炎症病理生理机制与精神障碍有关，并且在过去十年中，人们对肠道微生物群及其与精神健康的关系越来越感兴趣。我们旨在系统地审查与健康对照相比患有精神障碍、双相情感障碍或抑郁症的患者肠道微生物群变化的研究。方法 我们系统地检索了数据库 CENTRAL、PubMed、EMBASE、PsycINFO 和 LILACS。主要结果是将患有精神障碍、双相情感障碍或抑郁症的患者的肠道微生物群与健康对照组进行比较。结果 我们确定了 17 项研究，涵盖 744 名患者和 620 名健康对照。最一致的微生物群变化是在门水平上放线菌丰度较高，厚壁菌门丰度较低，在家庭水平上毛螺菌科丰度较低，而对于整体精神障碍而言，粪杆菌属水平上丰度较低。然而，我们发现所有研究都存在偏倚风险，并且纳入的研究在储存方法、粪便样本分析、结果报告和使用的统计数据方面存在很大差异。结论 由于纳入研究的许多局限性，应谨慎解释研究结果。需要更大规模的研究（尤其是精神分裂症和重度抑郁症），