Objective: To review the data from randomized controlled trials (RCTs) for the roles of microbiota, pre-, pro- and synbiotics in metabolic conditions (obesity, prediabetes, and diabetes mellitus type 2 [DM2]).
Methods: Primary literature was reviewed on the topics including RCTs of pre-, pro- and synbiotics use for metabolic disease.
Results: Gut bacteria (microbiota) benefit digestion and have multiple other functions. Microbiota could increase harvesting of energy from the food and cause subclinical inflammation seen in metabolic disorders. Diet-related interventions including prebiotics, probiotics, and synbiotics (combining pre-and probiotics) may benefit metabolic conditions. Prebiotics are complex carbohydrates (i.e., dietary fiber). Results of RCTs of prebiotics suggested a neutral effect on body weight, decreased fasting and postprandial glucose, and improved insulin sensitivity and lipid profile. Some inflammation markers were reduced, sometimes substantially (20-30%). RCTs for probiotics demonstrated significant but small effects on body weight (<3%) and metabolic parameters. The effect was seen mostly with fermented milk or yogurt compared to capsule form, consumption for at least 8 weeks, and use of multiple rather than a single bacterial strain. Changes in microbiota were seen at times with both pre- and probiotics. Pickled and fermented foods, particularly vegetables and beans, could serve as a dietary source of pre-, pro-, and synbiotics. These foods showed possible benefits for morbidity and mortality in prospective cohort studies.
Conclusion: Pre-, pro-, and synbiotics could prove useful, but further research is needed to clarify their clinical relevance for the prevention and management of metabolic disease.
Abbreviations: A1c = glycohemoglobin A1c CI = confidence interval CVD = cardiovascular disease GMB = gut (large bowel) microbiota DM2 = diabetes mellitus type 2 HOMA-IR = homeostatic model assessment of insulin resistance LDL = low-density lipoprotein LPS = lipopolysaccharide NAFLD = nonalcoholic fatty liver disease RCT = randomized controlled trial SMD = standardized mean difference TG = triglycerides.