Validation of fat mass metrics in pediatric obesity.

Introduction Hudda-Index is a prediction model for fat mass (FM) based on simple anthropometric measures., FM is a crucial factor in the development of comorbidities, i.e., type 2 diabetes. Hence, Hudda-Index is a promising tool to facilitate identification of children at risk for metabolic comorbidities. It has been validated against deuterium dilution assessments, however, independent validation against the gold-standard for body composition analysis, magnetic resonance imaging (MRI), is lacking. The aim of this study is to validate FM calculated by Hudda-Index against FM measured by MRI. The secondary aim is to compare Hudda-Index to other anthropometric measures including body mass index (BMI), BMI-standard deviation score (BMI-SDS), waist/hip-ratio, waist circumference (WC) and skinfold thickness. Methods The study cohort consists of 115 individuals between the age of 9 and 15 years, recruited at Paracelsus Medical University Hospital in Salzburg (Austria) and Uppsala University Children's Hospital (Sweden). Anthropometry, blood samples, and oral glucose tolerance tests followed standard procedures. MRI examinations were performed to determine visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). Results BMI and WC showed slightly stronger associations with the reference standard VAT (r=0.72 and 0.70, p<0.01, respectively) than Hudda-Index (r= 0.67, p<0.01). There is an almost perfect linear association between BMI and Hudda-Index. Accordingly, BMI and Hudda-Index both showed an acceptable association with cardiometabolic parameters. VAT was strongly associated with markers of liver status (LFF r=0.59, p<0.01) and insulin resistance (HOMA-IR r=0.71, p<0.01) and predicted metabolic dysfunction-associated steatotic liver disease (MASLD). Conclusion BMI, although an imperfect measure, remains the most reliable tool and estimates cardiometabolic risk more reliably than other anthropometry-based measures.