The impact of botanical fermented foods on metabolic syndrome and type 2 diabetes: a systematic review of randomised controlled trials

Our systematic review assessed the impact of botanical fermented food (BFF) consumption on glucose, lipid, anthropometric, inflammatory and gut microbiota parameters, in adults with metabolic syndrome (MetS), MetS components or type 2 diabetes mellitus (T2DM). Embase, MEDLINE, Cochrane CENTRAL and Google Scholar were searched with no language limits, from inception to August 31, 2022, for eligible randomised controlled trials (RCTs). Two independent reviewers screened 6873 abstracts and extracted relevant data. Risk of bias (ROB) was assessed using the Cochrane Collaboration's ROB2 tool. The final review included 26 RCTs, with 31 reports published between 2001 and 2022. Significant (p<0.05) within-group and between-group changes in cardiometabolic outcome means were reported in 23 and 19 studies, respectively. Gut microbiota composition was assessed in four studies, with two finding significant between-group differences. No significant difference between groups of any measured outcomes was observed in five studies. There were 14 studies at low ROB; ten were of some concern; and two were at high ROB. In 73% of included studies, BFF consumption by participants with obesity, MetS or T2DM led to significant between-group improvements in discrete cardiometabolic outcomes, including fasting blood glucose, lipid profile, blood pressure, waist circumference, body fat percentage, and C-reactive protein. BFF consumption increased the abundance of beneficial gut bacteria, such as Bifidobacterium and LAB, whilst reducing potential pathogens like Bacteroides. To determine the clinical significance of BFFs as therapeutic dietary adjuncts, their safety, tolerability and affordability must be balanced with the limited power and magnitude of these preliminary findings.