Allergy prevention: long duration of breast feeding vs early exposure to allergens - how does that fit together?

Question

So, as a proud father of a two-months old daughter, whose mom has many rather strong allergies and heavy asthma passed down through several generations we'd like to suppress her developing of allergies and especially asthma as far as possible. However, I kind of get conflicting information on the best path towards allergy prevention (or suppression):

Our midwife tells us that long duration of exclusive breastfeeding is best to prevent allergies. Indeed, this study (Ekelund et al. 2021): https://internationalbreastfeedingjournal.biomedcentral.com/articles/10.1186/s13006-020-00352-2 finds that long duration of breastfeeding can improve wheeze and allergic rhinoconjunctivitis (ARC) but not asthma or eczema If I read the paper correctly, the study doesn't evaluate for exclusive breastfeeding though. Anyways, while inconclusive for asthma and eczema, wheeze seems to be a factor for developing asthma: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5408007/ Since the study didn't target parents and children with genetic predisposition towards asthma, I guess that the inconclusivity towards asthma might be due to a too small number of participants (~6800).

On the other hand, allergenic foods e.g. peanuts (my wife is extremely allergic to those), should be done no less than after 4-6 months (Trogen et al. 2022): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9268235/ They write:

Until 2008, clinical practice guidelines from the American Academy of Pediatrics (AAP) and other professional societies recommended delaying the introduction of allergenic foods, such as peanut, until 3 years of age. This recommendation was based on the theory that the lack of exposure to allergenic foods during early infancy—which was posited to be a developmental window of high susceptibility—would prevent later development of allergy.

Now obviously, the introduction to allergenic foods should happen earlier if the child develops eczema, with the idea that intact allergenic proteins sensitize the immune system faster through the destroyed skin barrier than through ingestion, because the proteins get degraded through the gastric acid and become thus less allergenic.

This leads me to the following question:

1. Besides the obvious fact that the gut flora is not yet fully developed, why not start giving solid food already in month e.g. 2 or 3?
2. Why has the theory of delaying allergenic food come up at all? There should be at least a plausible scientific hypothesis behind this argumentation, shoudn't it?

Thanks a lot!

(These posts are likely related:

Does early exposure protect against developing allergies later on in life?

Rising allergy and intolerance diagnosis rates

Can foods one is not allergic to exacarbate atopic dermatitis?)

Answer 1

I’m going to focus in on your numbered questions.

I have also answered your related question.

Question 1

From First Bites—Why, When, and What Solid Foods to Feed Infants:

There also appears to be a sensitive period between 4 and 9 months when infants are most receptive to different food textures. There remains debate about when it is best to begin introducing solid foods into an infant's diet however, the available evidence suggests that provided the water and food supply are free of contamination, and the infant is provided adequate nutrition, there are no clear contraindications to feeding infants complementary foods at any age. There is emerging evidence that introduction of solid foods into an infant's diet by 4 months may increase their willingness to eat a variety of fruits and vegetables later in life, decrease their risk of having feeding problems later in life, and decrease their risk of developing food allergies, and the early introduction of solid foods into an infant's diet does not appear to increase their risk of obesity later in childhood.

This is reassuring for early introduction of food. However, there are still concerns about choking and eating solids resulting in the infant taking less breast milk (and this fluid). Breast milk contains everything baby needs for the first months of life, so there is no direct nutritional benefit to early solids.

The NHS guidance still recommends food at six months, whilst acknowledging individual variation in when infants are ready. Some of the reasons given are:

• Breast milk or first infant formula provide the energy and nutrients your baby needs until they're around 6 months old (with the exception of vitamin D in some cases)
• If you're breastfeeding, feeding only breast milk up to around 6 months of age will help protect your baby against illness and infections
• Waiting until around 6 months gives your baby time to develop so they can cope fully with solid foods
• Your baby will be better at moving food around their mouth, chewing and swallowing it – this may mean they'll be able to progress to a range of tastes and textures

So in summary, this is a balance between safety and prioritisation of breast milk and the emerging evidence that early exposure to foods reduces the risk of allergy and seems to encourage a wider range of tastes. There is no evidence that early food introduction aises obesity.

Question 2

Regarding early introduction of hydrolysed formula with the intention of reducing allergies, I found this in Early exposure to food and food allergy in children:

For many years, the prevailing advice for preventing food allergy in infants at high risk (ie, those with first-degree relatives with allergic conditions such as atopic dermatitis, food allergy, asthma, or allergic rhinitis) was to delay introduction of potentially allergenic foods (eg, delay peanut exposure until 3 years of age). However, this advice was based mainly on expert opinion and not evidence-based recommendations.

Now we have stronger evidence that it is better to not delay introduction of foods. Some are listed in the above paper, such as Early consumption of peanuts in infancy is associated with a low prevalence of peanut allergy By Du Toit et al.