Background Age, race, and analytic method influence levels of blood amino acids, of which reference intervals are required for the diagnosis and management of inherited metabolic disorders. Objectives To establish age-specific reference intervals for blood amino acids in Thai pediatric population measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). Methods A cross-sectional study of 277 healthy children from birth to 12 years was conducted. Anthropometric, clinical, and dietary information were recorded. Dried blood spots on a filtered paper were used for measurement by derivatized LC-MS/MS. Factors that might affect amino acids such as fasting time and dietary intake were analyzed using quantile regression analysis. Results Levels of thirteen blood amino acids were reported as median and interval from 2.5th–97.5th percentiles. Compared with those of Caucasian, most blood amino acid levels of Thai children were higher. Compared with a previous study using HPLC in Thai children, many amino acid levels are different. Glycine, alanine, leucine/isoleucine, and glutamic acid sharply decreased after birth. Citrulline, arginine, and methionine stayed low from birth throughout childhood, whereas phenylalanine was at middle level and slightly increased during preadolescence. Conclusion Reference intervals of age-specific blood amino acids using LC-MS/MS were established in the Thai pediatric population. They diverge from previous studies, substantiating the recommendation that, for the optimal clinical practice, age-specific reference intervals of amino acids should be designated for the particular population and analysis method.

Inulin might improve body composition in obese children. We aimed to determine the effects of inulin supplementation on body composition and metabolic outcomes in obese children. A randomized, double-blinded placebo-controlled study was conducted in obese Thai children aged 7–15 years. Participants were assigned to 3 treatment groups for 6 months: 13 g of extracted inulin powder from Thai Jerusalem artichoke, isocaloric maltodextrin, and dietary fiber advice groups. Body composition was assessed by bioelectrical impedance analysis. One-hundred and fifty-five children completed the study (mean age 10.4 ± 2.2 years, BMI z-score 3.2 ± 1.0, 59% male). The drop-out rate was 6%. The inulin extract yielded more than 90% compliance without significant gastrointestinal side effects. All three groups demonstrated a significant decrease in BMI z-score, fat mass index (FMI), and trunk FMI, but the differences between groups were not observed. Fat-free mass index significantly increased only in the inulin group (16.18 ± 1.90 vs. 16.38 ± 1.98 kg/m2, P = 0.009). There were no significant differences in the metabolic profiles between groups. Despite showing no substantial effect on adiposity, inulin may increase fat-free mass in obese children. Further research in the change of gut microbiota composition is needed to determine inulin’s impact on host-microbe interaction in pediatric obesity.