Metabolic Effects of Differential Organ Growth Rates

Study Overview
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Brief Summary
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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..

Detailed Description
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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.

Official Title
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Metabolic Effects of Differential Organ Growth Rates

Conditions
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Resting Energy Expenditure

Participation Criteria
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Eligibility Criteria
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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

Ages Eligible for Study
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Minimum Age: 7 Years
Maximum Age: 11 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Prepubertal children<br>Healthy 7-11 year old girls and boys. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Resting energy expenditure in kilocalories | REE is measured by indirect calorimetry over a 30 minute period and extrapolated to a 24 hour period | Day 1 | 
| Fat mass in kilograms | Measured from a whole-body dual energy X-ray absorptiometry (DXA) scan | Day 1 | 
| Fat-free mass in kilograms | Measured from a whole-body dual energy X-ray absorptiometry (DXA) scan | Day 1 | 
| Height in meters | Measured using a stadiometer | Day 1 | 
| Weight in kilograms | Measured using a calibrated scale | Day 1 | 
| Liver in kilograms | Total volume measured by MRI | Day 1 | 
| Heart in kilogram | Left ventricular mass measured by cardiac gated MRI | Day 1 | 
| Kidneys in kilogram | Total volume measured by MRI | Day 1 | 
| Spleen in kilograms | Total volume measured by MRI | Day 1 | 
| Trunk high metabolic rate organs in kilograms | The sum of liver, kidneys, spleen, and heart | Day 1 | 
| Brain mass in kilogram | Total volume measured by MRI | Day 1 | 
| Skeletal muscle mass in kilograms | Skeletal muscle volume measured by MRI | Day 1 | 
| Residual fat-free mass in kilograms | Fat-free mass minus the sum of kidneys, liver, spleen, heart, and skeletal muscle | Day 1 | 
| Total body adipose tissue mass in kilogram | Represents the sum of visceral, subcutaneous, and intermuscular adipose tissue by MRI | Day 1 | 
| Body mass index in kg/m2 | Weight and height will be combined to report BMI | Day 1 | 
| Variability in resting energy expenditure | The collected measures will be aggregated to statistically test the following question: How much of the variability in resting energy expenditure can be accounted for by the mass of the measured organs (liver, kidneys, spleen, heart) and tissues (fat, skeletal muscle, brain) and is the explained variance greater than the variance explained when predicting resting energy explained from a model using fat and fat-free mass alone. | Day 1 | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in resting energy expenditure in relation to changes in body composition and organ mass. | A portion of age-related decline (2-years) in daily REE adjusted for FFM observed in children is explainable in part by changes in the relative fractions of body mass as high (brain, heart, liver, kidney) and low (skeletal muscle, adipose tissue) metabolic activity tissues with growth and pubertal progress | From baseline measure to follow-up, approximately 2 years | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Fat-free mass, Tanner stage 1, Pre-pubertal