Mechanisms of Action and Critical Appraisal of Preclinical and Clinical Evidence for Green Banana (Musa spp.) and Banana-Derived Preparations in Obesity, Metabolic Syndrome and Type 2 Diabetes: A Narrative Review

Background: Obesity, metabolic syndrome (MetS) and type 2 diabetes (T2D) share chronic low-grade inflammation, insulin resistance and gut dysbiosis. Green banana pulp provides type-2 resistant starch (RS2), whereas other constituents—including phenolics—occur in tissue- and cultivar-dependent profiles. This narrative review critically appraises banana-derived preparations in relation to adiposity, glycaemic control, inflammation and the gut–liver axis. Preparation-level effects are distinguished from findings on isolated compounds and from mechanisms established with other sources of resistant starch or polyphenols. Methods: The core literature search covered PubMed, Scopus, Web of Science and ScienceDirect for 2000–2025. Historical and contextual sources were considered separately, and reporting was guided by SANRA. Results: Banana starch and fibre interventions modify the microbiota and increase short-chain fatty acid concentrations in rodents. The broader resistant-starch literature supports a fermentation-dependent GLP-1/PYY pathway, but the complete pathway is not established for banana preparations in humans. Banana extracts show enzyme-inhibitory, anti-adipogenic and anti-inflammatory activities in preclinical models. These cannot generally be assigned to phenolics alone, and some individually tested constituents are non-polyphenolic. Several links in the gut–liver pathway and adipose-tissue macrophage reprogramming remain unverified with banana preparations. Some short-term human studies report lower postprandial glycaemia, whereas longer studies provide inconsistent evidence and limited between-group support. Conclusions: Preclinical support is coherent and justifies further investigation of characterised banana preparations in order to conclude on clinical efficacy or permit the general attribution of their effects to individual compounds.