Skin carotenoids indicate diet, serum carotenoids, and inflammation across obesity and metabolic status in children

To validate reflection spectroscopy (RS)-based skin carotenoids (SCS) as non-invasive biomarkers of fruit and vegetable intake (FVI) in children and adolescents with obesity and metabolic dysfunction. This case-control study (China, 2023) included 210 children and adolescents aged 7–17 years, categorized into five groups: healthy weight (n = 30), overweight (n = 23), obesity (n = 25), obesity with one metabolic disorder (n = 56), and obesity with two or more metabolic disorders (n = 76). SCS levels were measured using RS, FVI was assessed via a food frequency questionnaire, serum carotenoids were quantified by high-performance liquid chromatography, and inflammatory markers were analyzed using flow cytometry. SCS and serum carotenoid levels decreased significantly across groups (p for trend < 0.001). SCS correlated strongly with serum carotenoids, except for lycopene, with the strongest association observed in children and adolescents with obesity and two or more metabolic disorders. A quartile increase in FVI resulted in an 11.92–45.98 unit increase in SCS, partially mediated by total serum carotenoids, beta-carotene, and beta-cryptoxanthin. SCS also inversely correlated with inflammation in metabolically disordered groups. RS-based SCS is a valid, non-invasive biomarker of FVI, closely related to serum carotenoids and inflammatory status, and effectively distinguishes metabolic dysfunction in children and adolescents.