Egg yolks, boosted with fatty acids, are a good way to give babies the nutrients they need during weaning, doctors say.

Babies change from milk to solids at between four and six months old.

Researchers writing in the American Journal of Clinical Nutrition said both breast-fed and formula-fed babies needed nutritional boosts at that time.

Breast milk does contain iron, but some babies can need more and the researchers say they may need to be given iron-rich weaning foods to prevent a deficiency, especially if they are over six months old.

Certainly eggs could be a suitable food to be introduced at around six months Kate Taverner, dietician

They add that during weaning, formula-fed babies can have too little docosahexaenoic acid (DHA), an omega-3 fatty acid which is essential for the growth and functional development of the brain.

Some companies are now starting to add DHA to their formula milk.

Egg yolks have both heme iron - which comes from animals and is more easily absorbed than iron from vegetables - and DHA.

They are also soft enough for babies to eat.

Fatty acid benefits

Researchers looked at the nutritional value of including two different varieties of egg yolks as weaning foods for a group of breast-fed and formula-fed infants.

A hundred and thirty-seven mothers and their babies took part in the study were recruited through immunisation clinics around Adelaide, Australia.

The babies, who were all around six-months-old, were randomly selected to receive either regular eggs, eggs enriched by feeding hens diets rich in n-3 fatty acids, or nothing.

Blood samples were checked at six and 12 months of age so that researchers could check DHA levels in red blood cells, in addition to iron status, and cholesterol levels.

They found the enriched eggs benefited both groups, with no negative effects on cholesterol concentrations, something UK dietary experts say is not a concern at that age anyway.

Both breast-fed and formula-fed babies who had been given n-3 fatty acid enriched egg yolks had 30-40% greater red cell membrane DHA levels than those fed normal egg yolks.

Iron levels were also increased.

The researchers suggest egg yolks are practical weaning foods, which babies tend to like.

The authors suggest future research should look at the physiological benefits of enhancing DHA in the latter part of infancy.

Suitable food

Kate Taverner, a paediatric dietician at St George's Hospital, London and member of the British Dietetic Association, told BBC News Online: "Certainly eggs could be a suitable food to be introduced at around six months."

She said studies had already shown DHA benefited babies born prematurely.

But Ms Taverner said there should be no worries about the amount of cholesterol in babies' foods.

"Messages for adults don't apply to children, certainly not at this age."