The Influence of Probiotic Supplementation on the Severity of Anxiety and Depressive Symptoms, as Well as the Function and Composition of Gut Microbiota, Metabolic, Inflammation, and Oxidative Stress Markers in Patients With Depression

The aim of this study is to gather empirical evidence which will enable to evaluate the impact of probiotic supplementation on the severity of anxiety and depressive symptoms, function, and composition of gut microbiota, metabolic parameters, inflammation, and oxidative stress markers in patients with diagnosed depressive disorders. The designed study will be prospective, randomized, placebo-controlled, and double-blind. The intervention period will last 8 weeks for each patient. The study will be conducted on 100 patients in total, who will be randomly divided into two groups, consisting of 50 patients each. Patients included in Group I (PRO-D) will receive one capsule daily containing a probiotic mixture at a daily dose of 3×109 colony-forming units (CFU). The probiotic will be composed of two bacteria strains: Lactobacillus helveticus Rosell®-52, Bifidobacterium longum Rosell®-175, and excipients: potato starch, magnesium stearate, and the capsule shell, made of hydroxypropylmethylcellulose. Patients included in Group II (PLC-D) will receive daily the same capsule, containing only excipients: potato starch, maltodextrin, and the capsule shell. The color, smell, and taste of the placebo will not be different from those included in the probiotic capsule. Patients will be considered compliant if they consume \>= 80% of the supplements. The primary outcome measures will be the severity of depressive anxiety and stress symptoms assessed with Montgomery-Åsberg Depression Rating Scale (MADRS) and the Depression, Anxiety, Stress Scale (DASS) with subscales scores, the quality of life level assessed with the WHOQOL-BREF instrument. The secondary outcomes measures will include: blood pressure (BP), body mass index (BMI) and waist circumference (WC) measures, fasting glucose (fGlc), HDL cholesterol (HDL-C), triglycerides (TG), white blood cells count (WBC), neutrofiles, serum levels of C-reactive protein (CRP), the level of faecal SCFAs, faecal microbiota α-diversity and the level of oxidative stress parameters (total antioxidant capacity (TAC) and malondialdehyde (MDA)) in the blood serum.