Young children have a high resting energy expenditure (REE) relative to their body weight and metabolically active compartment, fat-free mass (FFM). Both body weight and FFM are, however, metabolically heterogeneous and include organs and tissues varying widely in specific metabolic rate (i.e., organ REE/kg/d). One prevailing hypothesis is that most, if not all, of the higher REE observed in young animals and children compared to adults can be accounted for by a larger proportion of high metabolic rate components such as brain, liver, and heart..

FFM was the traditional and only means of adjusting REE for between-individual differences in metabolically active tissue components. The investigators seek to improve the understanding of variation in REE by developing new and improved rapid magnetic resonance imaging (MRI) methods of quantifying some of the major heat producing organs and tissues in children and adults. The long-term aim is to provide an improved understanding of human energy requirements. Specifically, the investigators propose to test whether: 1) a portion of the elevated daily REE adjusted for FFM observed in young children (Tanner Stage 1) could be accounted for by the relative fractions of body mass as high metabolic activity tissues (heart, liver, kidney, brain) and low metabolic activity tissues (skeletal muscle, adipose tissue), 2) a portion of the age-related decline in daily REE adjusted for FFM observed in children could be accounted for by changes in the relative fractions of body mass as high and low metabolic rate tissues during growth.

Inclusion Criteria:

• Healthy
• Aged from 7-11 years
• Pre-pubertal (based on Tanner staging)
• Africa-American, Asian, and Caucasian (by self-report of all 4 grandparents of same race group)

Exclusion Criteria:

• Actively involved in a weight management program
• Have co-morbidities of obesity (Blounts disease, hypertension, diabetes; sleep apnea)
• Have entered puberty
• Precocious puberty
• Have known metabolic abnormalities
• Were born prematurely, or were small or large for gestational age
• Lean individuals who have a family history (parents or siblings) of obesity or Type 2 diabetes
• Current or previous significant use of any medication known to affect any of the variables being measured

Subjects will be healthy African-American, Asian (Chinese, Korean, Japanese), and Caucasian pre-pubertal females and males (ages 7-11 years) at baseline. Lean (Body mass index (BMI) < 85th by age and sex) and obese (BMI > 95th percentile by age and sex.