One of the most frequently asked questions of allergists–besides “Why are there more people with allergies” (for which there is no single answer and is still considered to be due to multiple possibilities ranging from antibiotic overuse to diesel exhaust)— is: What can pregnant and postpartum women do to prevent food allergies and other allergic conditions from occurring in their children. I had the opportunity to attend a lecture about this at the annual meeting of the American College of Allergy, Asthma and Immunology in Houston earlier this month. Unfortunately, to use the words of a certain former US Secretary of Defense who was a US Congressman from this district in the 1960s and who is prone to being ridiculed, there are still known unknowns…and probably unknown unknowns as well.
The speaker at the meeting was a dietician from Children’s Hospital Colorado. She presented her research data that showed a decrease by 33% in the likelihood of food allergy over the first 10 years of life for each additional score in food diversity when the infants were 6 months old. Another 2019 study she cited came from a different lead author at her hospital and showed results suggesting that a pro-inflammatory diet during pregnancy is associated with an increased risk of asthma in offspring. Advice on which foods are pro-inflammatory (bad for you) and which foods are anti-inflammatory (good for you) can be found at https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/how-to-use-food-to-help-your-body-fight-inflammation/art-20457586. She also reviewed the medical literature about pregnant women eating a Mediterranean diet. Three of four studies showed that a Mediterranean diet was not associated with development of allergic diseases in offspring.
In spite of some suggestive studies, she said that there are still no clear recommendations from experts about mothers eating a certain diet. She still advocated for pregnant and postpartum women to (a) eat a varied diet and (b) to not avoid eating food that are most often associated with food allergic reactions. The second of her recommendations is supported by the 2019 update from the American Academy of Pediatrics about the effects of nutritional changes on the development of atopic (i.e. allergic) disease. This update does consider any duration of breastfeeding beyond 3-4 months to be protective against wheezing in the first two years of life. However, the update makes no conclusions about the amount of breastfeeding that would prevent specific food allergies. And, the studies in the medical literature are conflicting about the role of all these in either causing or preventing food allergies: vitamin D; omega 3 fish oil; probiotics.
Every parent wants the best for their children. Is it then right for a parent to feel blame about what was done or not done during pregnancy when an allergic condition develops? Shakespeare wrote in Julius Caesar: “The fault, dear Brutus, is not in our stars/But in ourselves.” While the line is helpful in reminding us that we are responsible for how we respond to life’s events, this wise advice should not paralyze us with guilt for our actions when we are not supplied with the right recommendations. From 2000 to 2008, the expert recommendations were for children to avoid eating peanut for the first two years of life. We now know that to be the wrong advice and that early introduction of allergenic solid foods—specifically peanut, egg and probably cow’s milk—has strong evidence for preventing food allergy to them. Until we have guidelines based on ample data and experience, we proceed with what we know well can reduce risk.