Fat-free mass hydration in newborns: assessment and implications for body composition studies.
Level 4 - case-series / case-control
Prospective observational validation and model comparison study
PubMed 21226759 · doi:10.1111/j.1651-2227.2011.02147.x
What was done
In healthy full-term infants, researchers measured the fat-free mass hydration factor (HF) and its biological variability in 12 newborns using Pea Pod air displacement plethysmography (for weight and volume) combined with isotope dilution (for total body water). They then compared body composition calculations between two conversion models ('Fomon' versus 'Butte') in a cohort of 108 infants evaluated at 1 and 12 weeks of age.
What was found
The measured fat-free mass hydration factor in newborns was 80.9%, showing low biological variability (0.8% of the average HF). Calculated body fat percentage was significantly lower using the Butte model than using the Fomon model at both 1 and 12 weeks, with a more pronounced difference observed at week 1. The measured HF closely agreed with the Fomon model.
Why it matters
Accurate assessment of infant adiposity requires valid biological assumptions regarding fat-free mass water content. These findings support the Fomon model as the more accurate conversion framework when assessing newborn body composition via Pea Pod.
Limits
The direct measurement of the hydration factor via isotope dilution was conducted in a small sample of only 12 newborns. The abstract omits exact numerical values for body fat percentages, confidence intervals, and p-values for the 108-infant comparison. Findings are restricted to healthy full-term infants and may not generalize to preterm or ill neonates.
Cited by
- context Excluding water, a newborn baby is composed of approximately 50% protein.