We also aim to determine if an intake of methionine and cysteine is more efficient to support glutathione synthesis rates in healthy children, than an equimolar intake of methionine alone. We will also evaluate whether arginine supplementation in obese children improves insulin sensitivity and protein synthesis, and explore gluconeogenesis under these conditions. A unique aspect of this project is that these functional assessments of amino acid utilization will be directly coupled with an in vivo assay of body cell mass, the major component of the body’s ‘metabolic engine’. The body composition data will provide an updated contemporary reference model, similar to the CDC curves for body mass index, that include the normal variations for a general multi-ethnic US healthy pediatric population.