Health benefits of anthocyanin-containing foods, beverages, and supplements have unpredictable relation to gastrointestinal microbiota: a systematic review and meta-analysis of random clinical trials

Anthocyanins are a type of natural pigment that has numerous health benefits. In recent years, the interaction of anthocyanins with gastrointestinal (GI) microbiota has been presented as a viable paradigm for explaining anthocyanin activities. The current study performed a systematic review and meta-analysis to determine the potential modulation of GI microbiota by anthocyanins in human health improvement. Clinical trials were retrieved from PubMed, Cochrane, Web of Knowledge, China Biology Medicine, China National Knowledge Infrastructure, and ClinicalTrials.gov with no language restrictions. Eight clinical trials (252 participants) were selected from the 1121 identified studies and the relative phylum abundance extracted from the trials was analyzed using a random-effects model. Based on the analysis, anthocyanins had no effect on the relative abundance of Firmicutes (standard mean difference [SMD]: -0.46 [-1.25 to 0.34], P = .26), Proteobacteria (SMD, -0.32 [-0.73 to 0.09], P = .13), nor Actinobacteria (SMD, -0.19 [-0.50 to 0.12], P = 0.24), but influenced the abundance of Bacteroidetes (SMD, 0.84 [0.17 to 1.52], P = .01) when compared with placebo/control. No significant influence on the relative abundance was detected when the data were analyzed following the "posttreatment vs. pretreatment" strategy. Our preliminary analysis revealed that the effects of anthocyanins on human GI microbiota vary between studies and individuals, and at the current stage, the clinical trials regarding the effects of anthocyanin interventions on human GI microbiota are lacking. More trials with larger sample sizes are needed to promote the clinical application of anthocyanins.