Solid evidence now exists to explain how food allergies can be prevented in infants. And the National Academies of Sciences (NAS) report recognizes the substantial and significant evidence from the LEAP study, which found that between 4 to 11 months, the introduction of peanuts is protective against peanut allergy in high-risk infants. In their prevention recommendations, the NAS committee advises healthcare practitioners and public health authorities to educate the public on the potential benefits of early introduction when the infant is ready (around six months).
On the other hand, breastfeeding, vaginal delivery, food allergen avoidance diets during pregnancy or lactation, and supplementing with nutrients like vitamin D and folate, and pre- and probiotics, are all behaviors that current evidence does not sufficiently support in preventing food allergy; according to the NAS report.
For example, there have been studies testing the relationship between route of delivery at birth and food allergies, which fall under the Microbial Hypothesis. Gut microbiota, or bacteria, is influenced by delivery. Infants have different microbiota depending on whether the mother gave a vaginal birth or had a cesarean section. While gut microbiota plays a role in immunity development, the NAS committee reported that only a few observational studies with limitations have been done to test the relationship between food allergies and delivery route, and therefore defined the existing evidence as limited. Furthermore, the committee does not predict strong evidence to come about, since it is unethical to force a population of woman to deliver a baby by cesarean section. They did, however, express the necessity of more prospective studies to support the hypothesis.
Additionally, the NAS report mentioned there are some food allergy prevention theories that have no valid research to back them, and do not warrant further research. An example is the widely-held theory that food additives and processed foods cause food allergies. The NAS report explains additives and preservatives in food allergy development have never been examined.
To validate theories of preventative measures (e.g. nutrient supplementation), the committee recommends sound research (using randomized controlled trials when possible) to substantiate evidence and provide the public with clear, science-based advice on food allergy prevention.