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

Objective To assess whether botanical fermented food (BFF) consumption has an impact on cardiometabolic biomarkers or gut microbiota in adults with obesity, metabolic syndrome (MetS) or type 2 diabetes mellitus (T2DM). Design Systematic review. Data sources Embase, MEDLINE, Cochrane CENTRAL and Google Scholar were searched with no language limits, from inception to August 31, 2022. Eligibility criteria. Randomised controlled trials (RCTs) investigating the effects of BFFs on glucose, lipid, anthropometric, inflammatory and gut microbial parameters, in participants with obesity, MetS or T2DM. Data extraction and synthesis. Two independent reviewers screened 6873 abstracts and extracted relevant data. Risk of bias (ROB) was assessed using the Cochrane Collaborations ROB2 tool. A qualitative, narrative synthesis was produced. Results. 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; nine were of some concern; and two were at high ROB. Conclusion. In 77% of included studies, BFF consumption by participants with obesity, MetS or T2DM led to significant improvements in some 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 Lactobacillus, whilst reducing Bacteroides. To determine the clinical significance of BFFs as therapeutic dietary adjuncts, their safety and tolerability must be balanced with the limited power and magnitude of these preliminary findings. Ethics. Ethical approval was not required as primary data was not collected. PROSPERO registration number. CRD42018117766