{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,29]],"date-time":"2026-07-29T09:01:12Z","timestamp":1785315672448,"version":"3.55.0"},"reference-count":18,"publisher":"MDPI AG","issue":"15","license":[{"start":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T00:00:00Z","timestamp":1785110400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background: The prevalence of pediatric obesity in Spain is among the highest in Europe. Although national surveillance reports a 4.5% decrease in excess weight, these primarily cross-sectional data may underrepresent the metabolic complexity observed in clinical settings. We aim to characterize the evolution of abnormal adiposity and to evaluate the transition probabilities between body mass index (BMI) categories in a multi-regional Spanish cohort. Methods: We analyzed Real-World Data (RWD) from 37,465 children and adolescents (ages 0\u201318) treated at HM Hospitales \u201cObservatorio de la Obesidad Infantil,\u201d between 2021 and 2026. Longitudinal BMI z-score trajectories were evaluated using continuous-time Markov chain models to determine transition probabilities between weight categories and identify developmental windows of adiposity plasticity. Results: At baseline, 21.6% of the cohort presented overweight\/obesity, with a higher frequency of overweight in females than males (13.0% and 11.2%, respectively; p &lt; 0.01) and obesity similar between sexes (~10%). Markov modeling identified a \u201ccritical window\u201d in children aged 2\u20135, who demonstrated a 75% probability of reverting to a normal weight. Conversely, children aged 6\u201311 entered an \u201cadiposity trap,\u201d characterized by a 60.0% obesity persistence rate and a 23.2% risk of progressing from overweight to obesity. A sharp initial drop in z-scores was observed immediately following the baseline clinical assessment across all groups. Conclusions: Our study reveals a significant window of opportunity for abnormal adiposity improvement between the ages of two and five, which contrasts with the adiposity inertia (diminished category fluidity) observed after age five.<\/jats:p>","DOI":"10.3390\/nu18152455","type":"journal-article","created":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T14:08:14Z","timestamp":1785161294000},"page":"2455","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Identifying the Critical Window and Adiposity Trap in Spanish Children: Longitudinal Evolution and Transition Probabilities of BMI Z-Scores from a Clinical Registry (2021\u20132026)"],"prefix":"10.3390","volume":"18","author":[{"given":"Juan P.","family":"Gonz\u00e1lez-Rivas","sequence":"first","affiliation":[{"name":"University Center for Health Sciences\u2013HM Hospitals (CUHMED), Camilo Jos\u00e9 Cela University, 28660 Madrid, Spain"},{"name":"HM Hospitales Health Research Institute, 28660 Madrid, Spain"},{"name":"Department of Epidemiology and Public Health, Harvard TH Chan School of Public Health, Boston, MA 02115, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mar\u00eda","family":"Rodrigo-Garc\u00eda","sequence":"additional","affiliation":[{"name":"HM Hospitales Health Research Institute, 28660 Madrid, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Amparo","family":"Rodr\u00edguez S\u00e1nchez","sequence":"additional","affiliation":[{"name":"Hospital Universitario HM Montepr\u00edncipe, HM Hospitales, 28660 Boadilla del Monte, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0008-8821-0462","authenticated-orcid":false,"given":"\u00c1lvaro","family":"D\u00edaz Conradi","sequence":"additional","affiliation":[{"name":"Hospital Universitario de Matar\u00f3, Consorci Sanitari del Maresme, 08304 Matar\u00f3, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-2167-1318","authenticated-orcid":false,"given":"Mar\u00eda","family":"Zelmira Bosch","sequence":"additional","affiliation":[{"name":"Hospital HM Nens, HM Hospitales, 08009 Barcelona, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1027","DOI":"10.1016\/S0140-6736(23)02750-2","article-title":"Worldwide Trends in Underweight and Obesity from 1990 to 2022: A Pooled Analysis of 3663 Population-Representative Studies with 222 Million Children, Adolescents, and Adults","volume":"403","author":"Phelps","year":"2024","journal-title":"Lancet"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Sharma, A., and Gurjeet Singh, T. 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