Current guidance advising mothers in the UK to exclusively breast feed for the first six months of their baby's life is being questioned by child health experts on bmj.com.

The authors, led by Dr Mary Fewtrell, a consultant paediatrician at the UCL Institute of Child Health in London, have reviewed the evidence behind the current guidance and say the time is right to reappraise this recommendation.

The researchers stress that while they fully back exclusive breast feeding early in life, they are concerned that exclusively doing so for six months and not introducing other foods may not always be in the child's best interests.

In 2001 the World Health Organisation (WHO) made its global recommendation that infants should be exclusively breast fed for the first six months. Many western countries did not follow this recommendation but in 2003 the UK health minister announced that the UK would comply.

Fewtrell and colleagues support six months exclusive breast feeding in less developed countries where access to clean water and safe weaning foods is limited and there is a high risk of infant death and illness. However they have reservations about whether the WHO's guidance about when to introduce other foods is right for the UK.

The WHO's recommendation that mothers should breast feed exclusively for six months is largely based on a systematic review undertaken in 2000 that considered existing research in this area, say the authors. This review concluded that exclusively breast fed babies have fewer infections and that the babies experience no growth problems.

Dr Fewtrell argues that the evidence that breast milk alone provides sufficient nutrition for six months is questionable. She says there is a higher risk of iron deficiency anaemia if babies are exclusively breast fed and that there could also be a higher incidence of celiac disease and food allergies if children are not introduced to certain solid foods before six months.

The authors also fear that prolonged exclusive breast feeding may reduce the window for introducing new tastes, particularly bitter taste which may be important in the later acceptance of green leafy vegetables. This could encourage unhealthy eating in later life and lead to obesity, they say.

Fewtrell and colleagues conclude that it is time to review the UK's guidance in the light of the evidence that has built up on this issue over the last ten years.