Feeding babies egg and peanut may reduce their risk of developing an allergy to the foods, finds a new study.

In the research, which is the largest analysis of evidence on the effect of feeding allergenic foods to babies, scientists from Imperial College London analysed data from 146 studies. In total the studies involved more than 200,000 children.

The study, which was commissioned by the UK Food Standards Agency, also found feeding children peanut, between the ages of four and eleven months, may reduce risk of developing peanut allergy. In addition, the team analysed milk, fish (including shellfish), tree nuts (such as almonds) and wheat, but didn't find enough evidence to show introducing these foods at a young age reduces allergy risk.

The research is published today in the Journal of the American Medical Association.

Although previous studies have found feeding children peanut and egg may reduce allergy risk, other studies have found no effect.

Dr Robert Boyle, lead author of the research from the Department of Medicine at Imperial, said: "This new analysis pools all existing data, and suggests introducing egg and peanut at an early age may prevent the development of egg and peanut allergy, the two most common childhood food allergies.

"Until now we have not been advising parents to give these foods to young babies, and have even advised parents to delay giving allergenic foods such as egg, peanut, fish and wheat to their infant."

Allergies to foods, such as nuts, egg, milk or wheat, affect around one in 20 children in the UK. They are caused by the immune system malfunctioning and over-reacting to these harmless foods. This triggers symptoms such as rashes, swelling, vomiting and wheezing.

"The number of children diagnosed with food allergies is thought to be on the rise", added Dr Vanessa Garcia-Larsen, a co-author on the study from the National Heart and Lung Institute at Imperial. "There are indications that food allergies in children have become much more common over the last 30 years.

The number of patients coming into our clinics has increased year-on-year, and allergy clinics across the country have seen the same pattern."

She added that the reasons behind this rise are still unclear - doctors may be better at recognising food allergy, or there may be environmental factors involved.

In the new study, called a meta-analysis, the team initially analysed 16,289 research papers on allergies and other immune system problems. Out of these, 146 were used for data analysis of when to feed babies allergenic foods such as egg, peanut, wheat and fish.

The results showed that children who started eating egg between the ages of four and six months had a 40 per cent reduced risk of egg allergy compared to children who tried egg later in life.

Children who ate peanut between the ages of four and eleven months had a 70 per cent reduced peanut allergy risk compared to children who ate the food at a later stage. However, the authors cautioned that these percentages are estimates based on a small number of studies.

Five studies (involving 1915 children) were used to estimate reduced risk of egg allergy, and two studies (involving 1550 children) were used to estimate reduced risk of peanut allergy. Therefore these figures may change when more studies are completed.

The team also calculated absolute risk reduction. They found that in a population where 5.4 per cent of people have egg allergy (the UK prevalence rate from one recent study), introducing egg between four and six months of age could prevent 24 cases of egg allergy per 1,000 people.

For peanut, in a population where 2.5 per cent of people have peanut allergy, introducing the food between four and eleven months could prevent 18 cases per 1,000 people.

The authors cautioned that the analysis didn't assess safety, or how many of the babies suffered allergic reactions from the early introduction.

Dr Boyle cautioned against introducing egg and peanut to a baby who already has a food allergy, or has another allergic condition such as eczema. "If your child falls into these categories, talk to your GP before introducing these foods." He also noted that whole nuts should not be given to babies or toddlers due to the choking hazard. "Whole nuts should be avoided in young children - if you decide to feed peanut to your baby, give it as smooth peanut butter."

The team also analysed whether introducing peanut, egg, milk, fish or wheat early into a baby's diet affected their risk of autoimmune diseases such as coeliac disease. The team found no effect on risk.

Commenting on the findings, the UK Food Standards Agency said: "Imperial College London has produced a high quality review.  The Government is considering these important findings as part of its review of complementary feeding for infants to ensure its advice reflects the best available evidence. 

Families should continue to follow the Government's current long-standing advice to exclusively breastfeed for around the first six months of age because of the health benefits to mothers and babies. "

The study was funded by the UK Food Standards Agency who commission research to understand the causes and mechanisms of food allergy and intolerance. The study was also supported by the Imperial NIHR Biomedical Research Centre, and the MRC-Asthma UK Centre in Allergic Mechanisms of Asthma 

"Timing of allergenic food introduction to the infant diet and risk of allergic or autoimmune disease: a systematic review and meta-analysis" by D. Ierodiakonou et al is published in JAMA

Case study: One family's experience of living with peanut and egg allergy 

Alexa Baracaia's son Sidney was diagnosed with egg and nut allergy when he was five months old.

"His first reaction was on Mother's Day in 2011, and was terrifying," recalled Alexa, a freelance writer from Stoke Newington in London. "My husband Paul had made me scrambled eggs for breakfast. Somehow we must have touched him with a trace of egg on our hands. It started with a few hives - resembling nettle rash - on his legs and within minutes he was scarlet, his face started to swell and the hives spread all over his body. He was screaming and very upset."

Alexa Baracaia with son Sidney, who has multiple allergies

Alexa's husband realised Sidney was having an allergic reaction and called an ambulance.

"Paul suffers from a condition that triggers an allergic reaction when he exercises, and so immediately recognised the symptoms," said Alexa.

Sidney was referred to a specialist allergy clinic where he was diagnosed with allergies to egg, tree nuts, peanuts, sesame, wheat, lentils, green peas and banana.

The family were given an Epipen - a pen-like device that injects adrenaline into the body in case of a life-threatening reaction - and told to carry it with Sidney at all times.

"The medical team were fantastic but it still came as a shock to discover he had so many serious allergies. I cried on the way home from the hospital."

Sidney had developed eczema all over his body at a few weeks old, which Alexa now knows can be a sign of food allergy.

"He was covered in red, scaly skin from a young age, but no-one suggested it could be a food allergy. We now know he was reacting to foods through my breast milk."

The family introduced solid food when Sidney was six months old, under the guidance of a dietician.

Sidney, now nearly six, has grown out of his allergies to banana, wheat and peas. But the family still need to be vigilant.

"When we go out I am that neurotic mother wiping down all tables and surfaces. When he was younger we would hover over him - like helicopter parents - at playdates and parties. We still need to be close by, and watchful, but he now understands he can't eat certain foods. We usually take his food with us if we go out.

"We also had to choose his school carefully, and made sure they understood the severity of his allergies. For instance, even in art classes he can't use egg boxes or lentils for crafts, as they could trigger a reaction."

Luckily the couple's three-year-old daughter, Sadie, does not have any allergies.

And although the new findings on early food introduction wouldn't have been appropriate for Sidney, as he already had eczema, Alexa believes new research is crucial to beating allergies.

"In the five years since Sidney was diagnosed, there has been a huge amount of new research published. These latest findings add to our knowledge. I'm hopeful for the future, and that there will be more treatments to tackle allergies - or even to prevent them altogether."