British Journal of Nutrition

Horizons in Nutritional Science

Duration of exclusive breast-feeding: introduction of complementary feeding may be necessary before 6 months of age

John J. Reillya1 c1 and Jonathan C. K. Wellsa2

a1 Division of Developmental Medicine, University of Glasgow, Yorkhill Hospitals, Glasgow G3 8SJ, UK

a2 MRC Childhood Nutrition Research Centre, Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK


The WHO recommends exclusive breast-feeding for the first 6 months of life. At present, <2 % of mothers who breast-feed in the UK do so exclusively for 6 months. We propose the testable hypothesis that this is because many mothers do not provide sufficient breast milk to feed a 6-month-old baby adequately. We review recent evidence on energy requirements during infancy, and energy transfer from mother to baby, and consider the adequacy of exclusive breast-feeding to age 6 months for mothers and babies in the developed world. Evidence from our recent systematic review suggests that mean metabolisable energy intake in exclusively breast-fed infants at 6 months is 2·2–2·4 MJ/d (525–574 kcal/d), and mean energy requirement approximately 2·6–2·7 MJ/d (632–649 kcal/d), leading to a gap between the energy provided by milk and energy needs by 6 months for many babies. Our hypothesis is consistent with other evidence, and with evolutionary considerations, and we briefly review this other evidence. The hypothesis would be testable in a longitudinal study of infant energy balance using stable-isotope techniques, which are both practical and valid.

(Received July 01 2005)

(Accepted August 11 2005)


c1 *Corresponding author: Dr John J. Reilly, fax +44 141 201 9275, email