This study intends to establish the feasibility of undertaking comprehensive metabolic phenotyping in infants. The overarching aim is to complete a prospective assessment of energy expenditure in the new infant metabolic chamber approximately one week apart to determine the accuracy and precision of infant protocols related to energy metabolism (sleeping metabolic rate, resting metabolic rate, diet-induced thermogenesis) and physical activity. This cross-sectional study will answer the following questions:~What is the test re-test reliability of measuring energy expenditure (sleeping metabolic rate, resting metabolic rate, diet-induced thermogenesis) in an infant under the same conditions, 5-7 days apart?~What is the reliability of 24h energy expenditure estimated by the infant metabolic chamber in comparison to a 7-day doubly labeled water study?~How do energy expenditure measurements in infants need to be adjusted to account for variability in infant size and body composition?
The purpose of this study is to measure energy expenditure during the first 3 months of life in infants.