Metabolically obese normal weight phenotype in children and adolescents aged 3 to 18 years: a systematic review

Background Children with normal Body Mass Index (BMI) may still exhibit adverse metabolic profile—termed as the metabolically obese normal weight (MONW) phenotype, placing them at increased risk of long-term cardiometabolic complications. Objective To systematically synthesise the evidence of the MONW phenotype in children and adolescents aged 3–18 years, and to identify early-life determinants. Methods This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines and searched PubMed/ MEDical Literature Analysis and Retrieval System On-Line (MEDLINE), Scopus, Web of Science (WoS), Google Scholar, Embase and Cochrane Library for studies from 2000 to January 2026. Observational studies of children and adolescents aged 3–18 years with normal BMI and at least one metabolic abnormality were included. Two reviewers independently screened the studies, extracted data and assessed risk of bias. Searches were conducted between March 2025 and January 2026, and 11 studies met the predefined inclusion and exclusion criteria. Results The reported prevalence of MONW ranged from 10.6% to 56.2%, varying by diagnostic criteria and population. Children with MONW consistently showed higher visceral adiposity, insulin resistance (IR), dyslipidaemia, hypertension, impaired glucose metabolism and elevated markers of low-grade inflammation despite having normal BMI. Early-life determinants included extremes of birth weight, rapid infant weight gain, adverse maternal metabolic status, unhealthy dietary patterns and sedentary behaviour. Overall risk of bias across studies was judged to be low to moderate, with the main concerns relating to residual confounding and use of heterogeneous MONW definitions. Conclusions MONW represents a clinically relevant but under-recognised paediatric phenotype. Reliance on BMI alone may delay identification of vulnerable children. Early risk stratification integrating metabolic proofing and central adiposity measures may enable timely prevention of long-term metabolic disease. Harmonised operational definitions of MONW and robust longitudinal life-course studies are required to inform evidence-based screening thresholds and preventive interventions.