(CNN) - Giving a baby a new food to try is fun, and it should be. The only concerns parents should have: finding their phones fast enough to document the funny faces and cleaning up the mess that might follow. Yet in recent years, scientific evidence has accumulated quickly on what foods to introduce when and how to best prevent allergies -- leaving parents to keep track of it all.
On Monday, based on a detailed review of all available evidence on the topic, the American Academy of Pediatrics published updated guidance on what works and what doesn't when it comes to the prevention of food allergies and other allergic conditions. The new guidelines continue to liberalize the introduction of what are thought to be highly allergenic foods such as peanuts, fish and milk.
There is no convincing evidence that delaying the introduction of allergenic foods beyond 4 to 6 months of age works in preventing food allergies, the report says. In addition, there is strong evidence that purposeful, early introduction of peanuts as early as 4 months may prevent the development of a peanut allergy in infants at high risk, defined in this report as those with a close relative with a history of an allergic condition.
"There is no reason to delay giving your baby foods that are thought of as allergens like peanut products, eggs or fish," Dr. Scott Sicherer, a co-author of the report, said in a statement. "These foods can be added to the diet early, just like foods that are not common allergens, like rice, fruits or vegetables."
The gastrointestinal tract is home to a unique set of immune system cells, and when these cells are given a taste of the allergenic proteins in different foods, they take up these proteins and become tolerant to them. Dr. David Stukus, a pediatric allergist and associate professor of pediatrics in the Division of Allergy and Immunology at Nationwide Children's Hospital, said that's true "as long as it's introduced early and in an ongoing fashion," meaning there is a critical window of time during which being introduced to these foods may lead the body to become tolerant.
And early means as soon as 4 months to 6 months of age, said Stukus, who was not involved with the new guidelines.
The report also looked at whether breastfeeding protects against eczema, wheezing, asthma and food allergies.
Exclusive breastfeeding for the first three to four months of life was found to be protective against eczema, the authors concluded. Any amount of breastfeeding beyond that time, even if not exclusive, was found to be protective against wheezing in the first two years of life and asthma in the first five years and even later. The report says no conclusion could be made when it came to breastfeeding and its effect on the prevention of food allergies.
No evidence was found that avoiding allergenic foods during pregnancy or during breastfeeding worked in the prevention of allergic conditions. Neither did the use of special hydrolyzed formulas, even in kids who were at high risk.
"I really appreciated the comprehensiveness of this clinical report," said Dr. Wendy Sue Swanson, a general pediatrician and chief of digital innovation at Seattle Children's Hospital.
Swanson, who has long advocated for the early introduction of a diversity of foods in young children, described feeling grateful for the guidance, given the ongoing changes in the understanding of allergy prevention.
How the thinking changed
In 2000, the American Academy of Pediatrics recommended delaying the introduction of cow's milk until children were 1 year old, egg until 2 years and peanuts, tree nuts and fish until 3 years.
"Recommendations were to avoid allergenic foods until children were older," Stukus said. "The thought process at the time was, well, if we avoid any exposure, maybe the allergic response won't develop."
In 2008, after a review of the available literature, the organization issued a report saying there was no convincing evidence that delaying allergenic food introduction prevented food allergies. The report did not give specific guidance as to when these foods should be introduced.
Almost 10 years later, after a study was published in the New England Journal of Medicine, the academy recommended that babies at high risk of developing peanut allergies be introduced to peanuts as early as 4 months. Infants considered at high risk included those with eczema and/or an egg allergy.
This study -- known as the Learning Early About Peanut or LEAP trial -- showed that children at high risk of developing peanut allergies who are introduced to peanuts at 4 months to 6 months old had a significantly lower risk of developing a peanut allergy than those who waited until they were 5 years; 1.9% of the kids who had peanuts early developed an allergy, compared with 13.7% of the kids who waited.
The LEAP trial formed the basis for Monday's new recommendations, which encourage the early introduction of peanut products in infants at high risk for allergies.
But most babies are not at high risk, and peanuts are just one of the eight culprit foods; the others are milk, eggs, fish, crustacean shellfish, wheat, soy and tree nuts, according to the US Centers for Disease Control and Prevention.
The evidence for other foods and children
The latest report explains that the same mechanism that protects infants at high risk is likely to protect infants at low or standard risk of developing food allergies.
A study that examined these other foods, known as the Enquiring About Tolerance or EAT trial, recruited 1,303 3-month-olds and randomly assigned them to receive six allergenic foods -- peanut, cooked egg, cow's milk, sesame, whitefish and wheat -- at that age or to wait until 6 months. The team then measured whether these infants developed food allergies between 1 and 3 years old.
Only 40% of parents were able to keep up with the diverse food frequency that the study protocol recommended. When researchers looked at the data from all of the children in the study, no difference was found in the rates of food allergies. When they looked at only the children whose parents had been able to keep up with the foods, there was a significant reduction in peanut and egg allergies.
"The EAT study provides some evidence but is less strong than the LEAP trial evidence," said Dr. Elizabeth Matsui, pediatric allergist and chairwoman of the American Academy of Pediatrics Section on Allergy and Immunology, comparing the trial that included the different foods to trial that involved peanuts. When the risk of an illness is relatively low, proving that it can be decreased even further is very difficult, she added.
An important takeaway from the trial is that introducing a variety of foods as early as 4 months is safe, Stukus explained.
Overwhelmingly, the data is pointing toward the benefit of early food introduction, Swanson said. "I don't want kids to delay introduction. Stop medicalizing this and let babies eat," she added.
The bottom line for parents
"It's not just early introduction. It's routine feeding. It's habituating. We need to make a habit of eating very diverse foods," Swanson said. "It's a great habit to have your whole life, because 50% of people who develop a food allergy develop it in adulthood."
In his practice, Stukus has started to recommend early introduction -- between 4 and 6 months of age -- of allergenic foods for all babies, no matter their individual risk. He encourages parents to continue to give these foods several times a week for babies who are tolerating them.
"I think the benefits far outweigh the risks in this situation," he said.
The most serious risk is anaphylaxis, a severe allergic reaction that can be life-threatening. But in most young infants, Stukus explains, anaphylaxis manifests as vomiting and hives, without the difficulty breathing and the closing airways that can be seen in older children.
Parents who spot vomiting or hives -- especially together -- should still seek medical attention. But pediatricians and parents alike can rest assured that these foods can be introduced freely at home, reversing decades of fear in the introduction of new foods, he added.
"We come from a place of restriction and medicalization," Swanson said. Pediatricians were strong in telling parents to be cautious, and now they must be strong in telling parents not to be cautious.
"No, I don't want you to be cautious. In fact, waiting might cause harm," she said.
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