Three scientists who controversially cast doubt on the safety of exclusively breastfeeding babies until six months old have links to infant formula and baby food companies, breastfeeding advocates say.

In a paper in the British Medical Journal, paediatrician Dr Mary Fewtrell and colleagues said exclusive breastfeeding to six months was associated with a higher risk of iron deficiency anaemia, food allergies and coeliac disease.

There was also a "relatively unexplored concern" that it may lead to children never developing a taste for bitter foods.

But breastfeeding advocacy group La Leche League New Zealand and the British children's charity Unicef United Kingdom have hit back.

La Leche director Alison Stanton said yesterday the paper was not new research but a report on studies selected by the four authors, of whom three had a conflict of interest because of their connections to infant formula and baby food industries.

The four said they received no external funding in preparing their paper but Dr Fewtrell and Alan Lucas, of University College London, and David Wilson, of Edinburgh University, said that in the past three years they had worked as consultants and/or received research funding from infant formula and baby food companies.

Unicef concluded: "Less breastfeeding and earlier introduction of solid food will lead to greater profit for this industry."

"Breastfeeding reduces the risk of infections, as well as the risk of diabetes and obesity in children and breast cancer in mothers."

Unicef said iron deficiency anaemia was related to the mother's iron levels, the length of gestation and cutting the umbilical cord too soon.

"Ensuring that the mother is not anaemic and that cord cutting is delayed will in turn ensure that the baby's own body-stores and breast milk will provide sufficient iron for over six months."

Unicef said the paper's intimation that early introduction of bitter tastes would increase acceptance of green leafy vegetables was speculative.

The World Health Organisation, in responding to the paper, has reiterated that evidence shows six months of exclusive breastfeeding is associated with a lower risk of gastro-intestinal infections for the baby, faster maternal weight loss after birth, and delayed return of menstrual periods.

The WHO recommends mothers exclusively breastfeed babies for six months, then add solid foods "and continue breastfeeding up to the age of 2 years or beyond".

La Leche League NZ and the Health Ministry advise introducing some solids from around six months.