Although serious food allergies are on the rise, parents can a build a child's food allergy tolerance even before birth, a Sydney-based gastroenterologist says.
Dr Vincent Ho's new book The Healthy Baby Gut Guide looks at what parents can do to help babies develop strong immune responses in their first 1000 days.
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He tells Kathryn Ryan there are several ways parents can minimise the risks of childhood food allergies and that diversity of gut microbes from an very early age plays a huge part. Many allergies are on the rise, recent figures show.
“The big four allergies are eczema, food allergies, asthma and allergic conjunctivitis, that used to be known as hayfever," he says. "We know that all of these allergies are on the rise and in fact, both in Australia and New Zealand, we know that the prevalence for asthma is extremely high in children.”
Statistics collected by the Ministry of Health identified a rise in the very severe food reaction anaphylaxis.
It is a potentially life-threatening reaction with numerous potential causes, with food allergy being the leading cause in children.
New Zealand figures, from 2002-2011, also found that seafood was the most common cause anaphylaxis followed by nuts.
“We know that with an immune reaction what happens is when a foreign substance is viewed as a threat by the body the body sets up a number of processes, including the production of antibodies to target that particular substance. What that can led to in some individuals is a very profound reaction.
“As part of that allergy is itchy skin and swelling, but what can also in some cases can be a more profound reaction like sudden drop in blood pressure due to the swelling of blood vessels. There can be respiratory issues like difficulty in breathing. All of those symptoms are really life-threatening and so when anaphylaxis occurs… it must be treated immediately.”
A common treatment is the administration of adrenaline.
Not all food allergies are the same and many children stop becoming allergic to certain foods as they enter adulthood, he says. But not all foods.
“We know that nine food allergies cause about 90 percent of all food allergies and… the ones children can outgrow are egg, wheat, soya and dairy…
“However, other allergies like peanuts, sesame, shellfish and fish, only a minority of children outgrow these and for most they are going to persist into adulthood and for the reminder of life.”
The rise of allergies has been linked to a hypothesis that children are not exposed to enough microbes to build adequate immunity against allergic diseases. He says this may be somewhat misleading.
“It is not about becoming unhygienic. I do think that you need to wash your hands and have sanitation measures, particularly in the era of covid-19.
“The hygiene hypothesis should be correctly restated to say that exposure to what we call ‘good microbes’ that have been around in the natural environment is what we’re actually missing.”
He says we are not getting exposed to these microbes because of environmental changes and because children are going raised in sterile urban environments.
“With caesarean sections, what we know is they are linked to an increase in the development of allergies, asthma and obesity.
“What is common with caesarean sections is administration of an antibiotic and that’s important to reduce the risk of infection… part of it also is the antibody exposure happening very early in life and what we find with that it decreases the diversity of microbes in the baby’s gut. That’s one of the changes that can happen with the introduction of antibiotics.”
The gut microbes found it babies delivered by caesarean section have been found to be from the mother’s skin, whereas gut microbes in babies delivered naturally have been found to be from the mother’s vagina. This too is believed to shape the baby’s immune response and disposition to allergies.
Genetics plays a part too, as does nutrition and chemical exposure. There are therefore things that can be done to minimise the risks.
“This is why mums can do a lot in terms of nutritional measures during pregnancy,” he says.
It is widely considered the baby’s gut is sterile within the womb, even though in 2014 there was some evidence suggested microbes were growing in the baby’s gut.
“During development even though we know that the baby’s gut is sterile what is interesting is it appears that babies can still be sensitised to the presence of allergens. Babies, for example, can be born with a sensitivity to a particular food allergen and that’s because some of these allergens can cross from the mother to the baby.”
This sensitivity can be modified to minimise it. The first trimester is particularly important in this respect, with exposure to allergenic foods helpful in developing immune resistance by the baby, evidence shows.
“That evidence is coming out that exposure can actually build immune tolerance early on. There is no evidence to suggest that excluding food allergens from the mother’s diet is helpful.”
The first two years shapes immunity. Breastfeeding is extremely important because what promotes certain types of bacteria species and diversity in the child’s gut.
“Particularly Bifidobacterium, which is important in breaking down some of the substances in breast milk and getting energy in the form of short-chain fatty acids to the baby.”
Bifidobacterium are a group of probiotics that normally live in your intestines and stomach. They help your body perform essential functions such as digestion and staving off harmful bacteria.
One of the biggest gut changes comes when the baby is being weaned off milk into solid foods, when there is a transitioning of gut microbes to similar to adults.
He supports the World Health Organisation’s recommendation of a minimum of six months’ breastfeeding, supplying enzymes and iron that would otherwise be in short supply.
Ho says continuing breastfeeding after this time while introducing solids and cow’s milk has a protective affect against allergenic reactions.
Introducing yogurt in the first year of life can help diversify microbes in the gut. During this time the immune system is being trained to respond to threats and a tolerance to foods we eat. The diversification of microbes helps in this process and lessens the possibility that the immune system will treat food stuffs as a threatening foreign object and mount a response.
Exposing toddlers to allergenic foods incrementally, slowly in small amounts to start observing any signs of a reaction, and then consistently, about three times per week afterwards, helps build tolerance.
"We know from some good data, certainly when it comes to peanuts, that children that were exposed to peanuts certainly in that first 12 months of life, it was found to be protective against peanut allergy at the age of five."