Measured versus predicted resting energy expenditure in infants: a need for reappraisal

The reliability of commonly used predictive equations for estimating energy expenditure in infants in both health and disease was assessed by comparing resting energy expenditure (REE, measured by indirect calorimetry) in relation to weight, height, and body cell mass (by total body potassium analysis) with predictive equations (Harris-Benedict, Food and Agriculture Organization/World Health Organization/United Nations University (FAO/WHO/UNU), Schofield weight-only, and Schofield weight-and-height equations) in 36 healthy infants (age 0.43 +/- 0.27 years; 19 male) and in 9 infants with cystic fibrosis (age 0.41 +/- 0.30 years; 4 male). Mean +/- SD REE for healthy boys was 0.205 +/- 0.019 MJ kg-1 day-1 and for healthy girls 0.217 +/- 0.026 MJ kg-1 day-1. Infants with cystic fibrosis had a significantly higher REE (0.258 +/- 0.034 vs 0.210 +/- 0.024 MJ kg-1 day-1; p < 0.005). Compared with measured values, predicted REE values varied markedly among equations, overestimating REE in healthy infants (Harris-Benedict equation, 182% +/- 63% (SD) of measured values; FAO/WHO/UNU equation, 104% +/- 14%; Schofield weight-only equation, 107.5% +/- 14%; and Schofield weight-and-height equation, 106% +/- 11%) and underestimating REE in those with cystic fibrosis (84% to 88% for the FAO/WHO/UNU, Schofield weight-only, and Schofield weight-and-height equations) except the Harris-Benedict equation (152%). On regression analysis both weight and body cell mass were related significantly to REE (r2 = 0.87 and r2 = 0.61, respectively) for normal infants and (r2 = 0.92 and r2 = 0.94) for those with cystic fibrosis. Using a generalized linear model of variance, we saw a significant (p < 0.001) variability among all REE measures. Thus we could rely on none of the predictive equations to give an accurate estimate of REE, and hence energy and fluid requirements, in individual infants. We suggest that when accurate estimates are needed, measurement of REE in individual infants should be attempted, especially in disease states, and that the continued use of current formulas should be reexamined.