Metabolic actions of the gut microbiota in obesity: a systematic review

Introduction: Obesity is a multifactorial disease that is difficult to manage and causes several comorbidities, such as physiological and mental disorders, diabetes, stroke, and depression. Worldwide, more than 2.3 billion people are overweight or obese. The gut microbiota interacts with several organs, including the brain, and can regulate metabolism, adiposity, homeostasis, energy balance, and central signaling of appetite and food reward. Objective: To explore and describe the metabolic actions of the gut microbiota and probiotics in the management of patients with obesity. Methods: The systematic review guidelines of the PRISMA Platform were followed. The search was conducted from August to November 2025 in the Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. Study quality was based on the GRADE instrument, and risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 125 articles were found. A total of 32 articles were fully evaluated, and 21 were included and developed in this systematic review. Using the Cochrane risk of bias tool, the overall assessment resulted in 23 studies with a high risk of bias and 25 studies that did not meet the GRADE and AMSTAR-2 criteria. Most studies presented homogeneous results, with X2=74.8%>50%. It was concluded that bidirectional signaling occurs within the gut-brain axis in the pathophysiology of obesity, mediated by metabolic, endocrine, neural, and immune system mechanisms. Fecal microbiota transplantation and supplementation with probiotics and prebiotics may be potential treatments for obesity. Diet is a determining factor for healthy colonization of the gut microbiota. Studies in obese humans also found a lower proportion of Bacteroidetes compared to those in normal-weight individuals. After weight loss, the proportion of Firmicutes is reduced and becomes more similar to that of lean individuals. Inulin supplementation can significantly promote intestinal bacterial diversity and improve gut microbiota dysbiosis in obese patients. Low-carb diets and time-restricted feeding are effective in weight management and produce profound changes in the gut microbiome and metabolome, in addition to caloric restriction.