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), physical activity, and sucking behavior. This cross-sectional study will answer the following questions: