The effects of probiotic and synbiotic supplementation on inflammation, oxidative stress, and circulating adiponectin and leptin concentration in subjects with prediabetes and type 2 diabetes mellitus: a GRADE-assessed systematic review, meta-analysis, and meta-regression of randomized clinical trials

PURPOSE: Probiotics or synbiotics consumption have been suggested to reduce the risk of cardiovascular disease (CVD) through a decline in inflammation and oxidative stress, however, the results from studies are conflicting. This study filled this knowledge gap by evaluating randomized controlled trials (RCTs) investigating probiotics or synbiotics intake on adipokines, inflammation, and oxidative stress in patients with prediabetes and type-2 diabetes mellitus (T2DM). METHODS: We systematically did search up to March 2022 in PubMed/Medline, Scopus, ISI Web of Science, and Cochrane library. A random-effect model was applied to estimate the weighted mean difference (WMD) and 95% confidence interval (95% CI) for each outcome. RESULTS: A total of 32 RCTs were included in the meta-analysis. This intervention led to a significant decrease in levels of C-reactive protein (CRP) (WMD − 0.62 mg/l; 95% CI − 0.80, − 0.44; p < 0.001), tumor necrosis factor-α (TNF-α) (WMD − 0.27 pg/ml; 95% CI − 0.44, − 0.10; p = 0.002) and malondialdehyde (MDA) (WMD − 0.51 µmol/l; 95% CI − 0.73, − 0.30; p < 0.001), and also a significant increase in levels of glutathione (GSH) (WMD 69.80 µmol/l; 95% CI 33.65, 105.95; p < 0.001), total antioxidant capacity (TAC) (WMD 73.59 mmol/l; 95% CI 33.24, 113.95; p < 0.001) and nitric oxide (NO) (WMD 7.49 µmol/l; 95% CI 3.12, 11.86; p = 0.001), without significant alterations in interleukin-6 (IL-6) and adipokines levels. CONCLUSION: A consumption of probiotics or synbiotics could be a useful intervention to improve cardiometabolic outcomes through a reduced inflammation and oxidative stress in patients with prediabetes and T2DM. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-022-03012-9.