Sleeping metabolic rate in early infancy

Date
2016
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University of Delaware
Abstract
In the United States, nearly two-thirds of infants receive infant formula by 3 months of age, either in combination with or fully replacing breast milk, the gold standard for infant nutrition growth. Studies have shown that formula fed infants, the majority of whom are fed cow’s milk formula (CMF), gain weight more rapidly than breastfed (BF) infants. Accelerated weight gain in early infancy is of concern as numerous studies have found an association between rapid infant weight gain and increased risk for overweight and obesity later in life. Not all infant formulas are alike in terms of composition and growth outcomes. Infants fed an extensive protein hydrolysate formula (EHF), which is comprised mainly of free amino acids and small peptides and has a slightly higher protein content than cow’s milk formula (CMF), have been found to gain weight similarly to BF infants. The energy balance mechanisms underlying the differences in weight gain by infant formula type are not known. However, it is possible that the different protein composition of the infant formulas (CMF versus EHF) impacts energy expenditure via differences in metabolic rate. This study had two overarching aims. First, we sought to determine the effect of formula type (CMF vs. EHF) on sleeping metabolic rate (SMR) in healthy, exclusively formula-fed infants. Second, we sought to utilize the measures of SMR to determine which of several available empirical equations for the calculation of metabolic rate in infants, was most accurate. ☐ A total of 141 mother-infant dyads were recruited from the greater Philadelphia area. At 0.75 months of age (baseline) when all infants were receiving CMF and again 3.5-months old, when all infants had been receiving their randomized formula for nearly three months, SMR was measured via indirect calorimetry. There were 102 infants with successful SMR at 0.75- months and SMR did not differ (p=0.148) by eventual formula randomization group. Eighty-three infants had successful SMR measurements at 3.5 months and formula type did not have a significant effect (p=0.9633) on SMR. At 0.75 months, we found that the Schofield weight only performed best for at the individual level at 0.75-months; it had the highest R2, suggesting good individual level agreement. At 3.5-month, the Schofield weight only and Oxford weight only equations performed best at the individual level. Since clinicians aim to calculate energy needs of individual patients, these analyses suggest the Schofield weight only is most accurate for estimating energy needs of 0.75 and 3.5 month old infants. These results are preliminary and will be repeated when the data set is complete.
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