Modulation of Glucose Homeostasis, Metabolic Endotoxemia and Circulating Short-Chain Fatty Acids Following Multi-Species Probiotic Supplementation: Findings from a 12-Week Randomised Placebo-Controlled Trial.

Background: Altered gut microbiota and gut-derived inflammation impair glucose regulation and promote metabolic endotoxemia, yet evidence on probiotic effects across combined glycaemic, inflammatory and short-chain fatty acid (SCFA) outcomes remains limited. This study investigated the effects of a 12-week multi-species probiotic on glucose homeostasis, incretin hormones, inflammatory biomarkers and circulating SCFAs in adults with subthreshold depression. Methods: In a 12-week double-blind, randomised, placebo-controlled trial, 39 adults with subthreshold depression were allocated to either a probiotic supplement containing Limosilactobacillus fermentum LF16, Lacticaseibacillus rhamnosus LR06, Lactiplantibacillus plantarum LP01 and Bifidobacterium longum 04 (n = 19) or placebo (n = 20). Fasting glucose, insulin, HOMA-IR, glucose-dependent insulinotropic peptide (GIP), high-sensitivity C-reactive protein (hs-CRP), lipopolysaccharide-binding protein (LBP), soluble CD14 (sCD14) and SCFAs were evaluated at three time points: baseline, week 6 and week 12. Between-group and treatment × time effects were analysed using general linear models. Results: Probiotic supplementation significantly reduced fasting glucose at 12 weeks compared with placebo (-1.8 vs. 0.1 mmol/L; p = 0.036). In the probiotic group, greater reductions in GIP (p = 0.012; p = 0.037), LBP (p < 0.001), sCD14 (p = 0.002; p = 0.001) and hs-CRP (p = 0.047) were also observed compared with placebo. Plasma SCFA concentrations remained largely unchanged, with no significant treatment × time interactions, except for higher valerate levels at 12 weeks in the probiotic group (p = 0.019). Conclusions: Twelve weeks of multi-species probiotic supplementation improved fasting glucose, reduced incretin and inflammatory biomarkers and attenuated metabolic endotoxemia, without alterations in circulating SCFAs. These findings support beneficial modulation of metabolic-immune pathways and highlight the promising role of probiotics to enhance glucose regulation and systemic inflammatory tone in adults with subthreshold depression.