Leslie Robinson,

JHL 11(3) 1995 has a commentary written by Hans Christofer Borrensen,
MD of Norway.  He looks at several studies and concludes that,
although the current policy of WHO/ UNICEF is to recommend the
introduction of solid food to breastfed infants between 4 to 6
months, breastmilk is sufficient for most infants until at least nine
months and for some infants until twelve months.  He looks at the
energy requirements of infants, infant health and growth, and iron
requirements.  He also looks at the mother's ability to produce
enough milk to exclusively breastfeed a 6 to 12 month old infant.  He
sites 23 references at the end of the article.

Hope this helps.

Dorothy Rae Collier, Moreno Valley, CA