Early and sustained allergen introduction to the infant diet may influence the risk of allergic or autoimmune disease for those patients who do not already exhibit allergic symptoms before one year of age. A meta-analysis of 146 studies concluded that early egg or peanut introduction was associated with a moderately lower risk of developing egg or peanut allergy.  Unfortunately, fish correlated with low and wheat and cow’s milk correlated with zero association to reduced allergy risk. [2-4]
Let’s take a closer look at the 146 study meta-analysis by Ierodiakonou (that is a mouth full, pun intended!). This M.D/Ph.D. and his associates compiled and compared all of the viable research they could get their hands and taught us this:
Analysis of 5 separate studies totaling 1915 participants showed moderate association between egg introduction at 4-6 months and decreased possibility of egg allergy. The risk reduction for a population with 5.4% egg allergy incidence was 24 cases per 1000 population. In other words, early introduction could save 24 people out of 1000 in typical conditions. Notably, 4 different trials with a total of 1786 participants showed zero association between introduction timing and sensitization rates.
Two trials with 1550 total participants found a lower peanut allergy risk after introduction at age 4-11 months. Risk reduction here was 18 cases per 1000 population, assuming common peanut prevalence around 2.5 %. Here too, one study of 1168 individuals found no association.
Three studies with 13472 individuals found early fish introduction around 6-9 months was associated with lower food allergies (all kin
ds) and rhinitis. This is hypothesized to be due to anti-inflammatory properties of omega-3 fatty acids. However, this association was found to be low-to-very low and full comparison of the data was not possible due to how differently the research was conducted between the three.
The Rest of the Early Introduction Allergy Story
As mentioned above, other allergens had no correlation found between early exposure and allergy risk. Early exposure is not related to cow’s milk allergy prevalence  or celiac disease . It is of note that there have been additional studies in cow’s milk protein allergy that were not included in Ierodiakonou’s publication. This could be due to the research funding coming from Dairy boards and/or companies which may indicate a conflict of interest and be grounds for dismissal. 
While early allergen ingestion may be beneficial for children who do not exhibit signs of food intolerance, the opposite is true when symptoms are present.
Food allergic patients under one year should avoid exposure of the culprit food until the infant is over one. Strict avoidance removes the chance of progressively harmful reactions at such a young age as well as increasing the possibility of outgrowing the allergy. [17, 18]
More research is needed to fully understand the potential risks and benefits of early allergen exposure. However, there has been an increased parental interest leading to early exposure products such as those developed by Lil Mixins. Lil Mixins offers peanut, baked egg, and tree nut powders with easy directions for early and often exposure.
Keep This In Mind As a Parent
Like many things allergy and breastfeeding, more research is needed.
Large-scale data analysis indicates that early exposure to egg and peanut may reduce risk of developing that particular allergy later in life.
Strict avoidance for infants who exhibit allergy symptoms! Unless medically-directed otherwise, wait to re-introduce until after 1 year and do so under medical supervision if necessary. You should always consult your child’s medical provider with any questions during this time.
Corresponding to the above research, the AAP states the following :
"In the EAT study on the timing of introduction of allergenic complementary foods in infants who were breastfed, all infants in the early introduction group (n = 567) were exclusively breastfeeding at 3 months of age and still breastfeeding at 5 months.17 Six different allergenic foods were introduced between 3 and 5 months of age (median age, 3.4 months): peanut (peanut butter), cooked egg (1 small hardboiled egg), cow's milk, sesame, whitefish, and wheat. In the standard introduction group (n = 595), the allergenic foods were not introduced before 5 months, at which time all infants were still breastfeeding but consuming up to 300 mL of formula per day. In the intention-to-treat analysis, food allergy developed in 5.6% of the subjects in the early introduction group (mostly breastfeeding) and in 7.1% of the subjects in the standard introduction group (mixed feeding), a difference that was not significant...For the prevalence of specific food allergies in the per-protocol analysis, there was a significant protective effect of early consumption of both peanuts (0% vs 2.5%; P = .003) and eggs (1.4% vs 5.5%; P = .009). This was not observed for any of the other allergenic foods introduced. The data were analyzed according to allergy outcomes and mean weekly dose ingested; consumption of 2 g/week of peanut or egg-white protein was associated with a significantly lower prevalence of these allergies, respectively, compared with less consumption."
Remember you’re not alone and we’re here to support you.
Ierodiakonou, Despo, et al. "Timing of allergenic food introduction to the infant diet and risk of allergic or autoimmune disease: a systematic review and meta-analysis." Jama 316.11 (2016): 1181-1192.
Chirdo, F. G., et al. "Presence of high levels of non-degraded gliadin in breast milk from healthy mothers." Scandinavian journal of gastroenterology 33.11 (1998): 1186-1192.
Kull, I., et al. "Fish consumption during the first year of life and development of allergic diseases during childhood." Allergy 61.8 (2006): 1009-1015.