Original Research Article
Infant sex predicts breast milk energy content
Version of Record online: 16 JUN 2009
Copyright © 2009 Wiley-Liss, Inc.
American Journal of Human Biology
Volume 22, Issue 1, pages 50–54, January/February 2010
How to Cite
Powe, C. E., Knott, C. D. and Conklin-Brittain, N. (2010), Infant sex predicts breast milk energy content. Am. J. Hum. Biol., 22: 50–54. doi: 10.1002/ajhb.20941
- Issue online: 4 DEC 2009
- Version of Record online: 16 JUN 2009
- Manuscript Accepted: 14 MAR 2009
- Manuscript Revised: 8 FEB 2009
- Manuscript Received: 14 DEC 2008
- Harvard College Research Program, Cambridge, Massachusetts
During human evolutionary history, and for many around the world, breast milk is the primary source of nutritional energy for infants. Variation in breast milk quality might logically have important effects on infant health, growth, and development, yet the sources of this variation remain largely unelucidated. We quantified nutrient and energy content of breast milk from 25 healthy, well-nourished Massachusetts mothers with infants aged 2–5 months. We examined several potential sources of variation in milk quality, particularly feeding patterns, infant sex, and maternal breast growth during pregnancy. After controlling for time since last feeding, a known correlate of milk composition, we found that mothers of male infants produced milk that had 25% greater energy content than mothers of female infants (P < 0.001). Change in maternal bra cup size during pregnancy was associated with 16.17 kcal/100 ml greater energy content of milk (P = 0.009), but was not significant after taking infant sex into account. Greater nutritional investment in sons may account for the greater observed growth rates in male compared to female infants. Am. J. Hum. Biol. 2010. © 2009 Wiley-Liss, Inc.