The purpose of this study is to investigate the effects of a synbiotic (ProSynbiotic) on the gut microbiota composition, body composition and adiposity-related genes and metabolic markers in healthy overweight adult subjects.

This is a parallel, double-blind, randomized, placebo controlled trial to determine the effects of a synbiotic formulation (ProSynbiotic) containing 4 billion CFU of a probiotic blend of Bifidobacterium lactis BB-12, Lactobacillus acidophilus LA-5, Lactobacillus casei 431 and Saccharomyces boulardii, along with 1 g of the prebiotic inulin and 100 mg of galactooligosaccharide (GOS) on the gut microbiota composition, body composition, expression of genes mediating dietary energy harvest and adiposity, and on adiposity-related metabolic markers in healthy free-living overweight or moderately obese subjects. The duration of the study is 18 weeks, including a 2-week run-in period before randomization of subjects into the synbiotic or placebo group, a 12-week intervention period, and a 4-week follow-up after the end of the intervention. During the intervention period, subjects will be instructed to take 3 capsules of either synbiotic or placebo per day and maintain their habitual diet and physical activity. They will also be asked to document any unusual symptoms or side effects as well as keep a bowel diary. Diet and physical activity will be monitored via 24-h dietary recalls and the global physical activity questionnaire respectively. Changes in the gut microbiota composition will be determined by measuring bacterial population levels in stool sampled collected at baseline, 6 weeks, 12 weeks and the follow up time point. Body composition will be measured using the BOD POD at baseline, 6 weeks, and 12 weeks. Gene expression levels will be assessed at baseline and 12 weeks in colonocytes (isolated from stool samples) and PBMCs (isolated from blood samples) by qPCR. Metabolic markers will be measured at baseline and 12-weeks in plasma or serum using the respective biochemical- or immuno-assays.

Inclusion Criteria:

• Age between 18-64
• BMI of 25-34.9 and/or a waist circumference >35 inches for women and >40 inches for men
• Generally healthy except for overweight or moderately obese
• A signed consent form
• Passed a screening questionnaire and willingness to comply with study procedures
• Lipid levels, fasting glucose, liver function and complete blood counts within the normal reference ranges as measured in a screening blood sample

Exclusion Criteria:

• Persons on a weight-loss regimen
• Antibiotic use (< 3 months before the study)
• Regular probiotic, prebiotic or synbiotic use (< 1 month before the study)
• Regular use of anti-inflammatory drugs, weight-loss medications or supplements (< 1 month prior to the study)
• Personal history of cardiovascular disease, hypertension, cancer, type 1 or type 2 diabetes and inflammatory gastrointestinal disorders such as Crohn's disease or colitis
• Smoking
• Consumption of >2 units of alcohol per day
• Pregnancy or lactation
• Irregular periods, menopause or hormone replacement therapy
• Over 300 minutes of exercise per week