Anthropometry is frequently used for nutritional assessment. Little is known in infants about the validity of anthropometric measurements in relation to whole-body fat (TBF) and fat-free mass (FFM) composition. We compared TBF and FFM estimations by total-body electrical conductivity (TOBEC) with anthropometry in 435 healthy infants ages 21-365 d. TBF was best correlated with weight-for-length and calf circumference (r2 = 0.84, r2 = 0.83). FFM was best correlated with body weight (r2 = 0.93). Upper-arm anthropometry, skinfold thickness, and Quetelet's and Ponderal indexes were poorly correlated with TBF and FFM (r2 < 0.65). New anthropometry-based prediction equations were calculated (r2 = 0.90 for TBF and r2 = 0.95 for FFM). New simple indexes (analogous to Quetelet's index) were calculated for TBF (weight x calf circumference/length; r2 = 0.87) and for FFM (square root of weight x length; r2 = 0.95). Prediction equations and indexes were cross-validated in a second population by a second observer. Interobserver variation was largest for equations with skinfold thicknesses included. We conclude that anthropometry can be used for rough estimations of infant body composition, although indexes different than those used in children and adults are preferred.

This study is the first to report approximations of energy requirements for male and female breast-fed and formula-fed infants based on individual estimates of total daily energy expenditure (TDEE) and energy deposition derived from total body fat (TBF) and fat-free mass (FFM) gain as determined by total-body electrical conductivity. In 46 healthy, full-term infants the effect of > or = 4 mo of exclusive breast-feeding compared with formula feeding on macronutrient and energy intake, TDEE, energy deposition, and growth were investigated prospectively. Metabolizable energy intake (MEI) was assessed from macronutrient intake by test weighing (MEI-TW) and from the sum of TDEE and energy deposition (MEI-Pred). At 1-2, 2-4, 4-8, and 8-12 mo of age MEI-Pred averaged 431 +/- 38, 393 +/- 33, 372 +/- 33, and 355 +/- 21 kJ x kg(-1) x d(-1) for boys, and 401 +/- 59, 376 +/- 25, 334 +/- 33, and 326 +/- 17 kJ x kg(-1) x d(-1) for girls. No significant difference between breast-fed and formula-fed infants was found with respect to weight, length, head circumference, TBF, FFM, and TDEE at all ages, or for gain in length, weight, TBF, and FFM. MEI-TW was significantly different between feeding groups at 1-4 mo of age (formula-fed being greater than breast-fed, P < 0.005). This feeding effect, however, was not significant for MEI-Pred (MJ/d). MEI-TW differed from MEI-Pred only in breast-fed infants at 1-4 mo (P < 0.05 at 2-4 mo). The data from this study indicate that energy requirements in infants are lower than the recommendations in guidelines currently in use.

Measurement of total-body electrical conductivity (TOBEC) has emerged as a rapid, safe, and reproducible method for estimation of infant total body fat (TBF). Agreement of two anthropometric methods [by Dauncey et al (1977) and Weststrate et al (1989)] with TOBEC-TBF was assessed in 435 healthy infants aged 21-365 d. Dauncey-TBF correlated with TOBEC-TBF by r2 = 0.61 and exceeded TOBEC-TBF by 0.14 +/- 0.25 kg in infants< 4 mo of age. Thereafter, TOBEC-TBF exceeded Dauncey-TBF by 0.20 +/- 0.47 kg. We modified Dauncey's method, which significantly improved the correlation to r2 = 0.75. Weststrate-TBF correlated with TOBEC-TBF by r2 = 0.87, but exceeded TOBEC-TBF by 0.5 kg. Both methods showed poor agreement with TOBEC-TBF. We conclude that both methods, although suitable for comparison of TBF between groups, cannot be used to accurately assess TBF in an individual infant.

Data on body composition in conjunction with reference centiles are helpful in identifying the severity of growth and nutritional disorders in infancy and for evaluating the adequacy of treatment given during this important period of rapid growth. Total body fat (TBF) and fat-free mass (FFM) were estimated from total body electrical conductivity (TBEC)