Gut microbiome-focused dietary interventions in weight management: causal evidence, precision nutrition and emerging gut-targeted therapies

Purpose This study aims to critically evaluate dietary and gut-directed strategies for weight management, distinguishing association from causation while integrating fibre structure, biomaterials, precision nutrition, microbial therapeutics and glucagon-like peptide-1 receptor agonist (GLP-1 RA) care. Design/methodology/approach A targeted narrative synthesis of human interventions, mechanistic studies, consensus statements, systematic reviews and preclinical studies was assessed for design, replication, clinical relevance and causal mediation. Findings Microbiome changes alone do not establish clinically meaningful mechanisms. Causal support is strongest from transfer experiments, short-term human faecal microbiota transplantation, controlled feeding and targeted metabolite delivery, although effects are often transient. Whole-food diets rich in diverse fibres, resistant starch, minimally processed plants and fermented foods remain the most mature strategy. Prebiotic effects vary with structure, dose, food matrix and host ecology; fibre–clay hybrids remain preclinical. Precision nutrition using multi-omics and machine learning is advancing, but external validation and superior weight-loss outcomes remain limited. Live biotherapeutics, engineered microbes, postbiotics and faecal microbiota transplantation differ in readiness, safety and regulation. Research limitations/implications Future trials require standardised outcomes, direct metabolomics, shotgun metagenomics, longer follow-up and prespecified mediation analyses. Practical implications Care should remain food-first, culturally adaptable and integrated with obesity therapies. During GLP-1 RA treatment, gradual fibre titration, hydration, smaller meals and symptom-specific foods may improve tolerability, although direct evidence is limited. Social implications Public health policy should improve access to minimally processed, fibre-rich foods and avoid deterministic microbiome claims. Originality/value This review provides an evidence hierarchy linking fibre structure, biomaterials, precision nutrition and microbial therapeutics to clinical weight-management decisions.