Caveat: I am not a medical doctor or an immunologist. The contents of this blog post are the results of my own research into food allergies. However, they should not be used in place of your own research and/or advice from your doctor.
Further caveat: I did not do a thorough review of the literature. I relied heavily on a few recent review articles. Not surprisingly, nothing I read contradicted the latest recommendations from the American Academy of Pediatrics (summarized here).
Food allergies scare me, and I think they scare most other parents, too. They are actually relatively rare- according to the FDA, only 1.5% of adults and 6% of children under 3 suffer from them. However, the consequences, particularly of nut and peanut allergies, can be devastating, so most parents want to do whatever they can to minimize their child's risk of developing these allergies.
I often hear people say that the incidence of food allergies is on the rise, at least in industrialized nations. I thought this, too, but the articles I read during my research indicated that there is no evidence of an increase in food allergies, only of an increase in the more common "hay fever" type allergies (1). It has been noted that people tend to perceive they have food allergies far more often than such allergies can be clinically documented. I think this is because people confuse a food intolerance (such as lactose intolerance) with an actual allergy. The British Medical Journal has a nice article on the difference between allergies and intolerance. True allergies involve an inflammation response. Intolerances often produce stomach upset and gas. For instance, I have written before about how I went off of dairy while Pumpkin was younger. I suspected that she was having trouble with the dairy in my diet due to her episodes of painful gas. However, I doubt she has an actual allergy.
I had several specific questions about food allergies. I don't have time to do a full, comprehensive review of the literature. Therefore, I did the same thing I used to do in graduate school when I wanted to learn about a new field: I relied heavily on review articles (articles summarizing the current state of a field, written by an expert in that field). Here is what I found about my specific questions:
1. Should I have restricted my diet while pregnant?
The evidence does not seem to support this, except perhaps for peanuts. In fact, one study I read about (reviewed in (2)), found that children whose mothers avoided cows' milk and eggs were actually more likely to have an egg intolerance in the short term. There was a study (also reviewed in (2) that shows a possible link between consumption of peanuts while pregnant and later development of peanut allergies in the baby. However, there was a rather important confounding variable: the study also found that peanuts and/or peanut butter were introduced at a younger age in the children with peanut allergies. Furthermore, the study was based on recall, and it is highly likely that mothers whose children went on to develop peanut allergies would remember eating peanuts better than mothers of non-allergic children.
2. Should I restrict my diet while breastfeeding?
The evidence is not strong here, either, unless you have a baby who has already shown signs of a food allergy (in which case you'll have to avoid that food). While it has been shown that the peanut allergen can pass into breast milk, the small study I found documenting this only found peanut allergen in the milk of 11 out of 23 women who consumed peanuts. (3) None of the reviews I read referenced conclusive studies about the impact of eating peanuts while breastfeeding. There are some studies suggestive of a link between maternal peanut-eating and development of peanut allergies in the baby (reviewed in 2), but also studies finding no such link (reviewed in 4).
There are studies indicating that avoiding common allergens (milk, egg, and fish) from the maternal diet can decrease the risk of the baby developing "atopic dermititis" (i.e., allergic eczema), but interestingly, the effect disappears as the children in the study age. At 6 months, there is a significant effect, but by 10 years, there were no significant differences between the children whose mothers ate milk, eggs, and fish and those whose mothers avoided these foods (reviewed in 2).
Most of the studies I read about looked at the impact of maternal diet on atopic dermatitis and asthma, rather than food allergy. I suspect this is at least partially due to the fact that food allergies are more rare.
3. Should I delay feeding my baby certain foods?
There really doesn't seem to be any good evidence on this, except for in the case of supplementing a baby "at high risk of developing atopic disease" (usually defined as a baby in which at least one parent or sibling has atopic disease, see question 4 below) with formula- in that case, there is some evidence that using an extensively hydrolyzed formula is preferable (1, 4).
The best argument I have seen for delaying the introduction of common antigens came from several of the commenters on Ask Moxie's post on this subject: a young baby can't tell you that his or her throat is itchy (a common first symptom of an allergic reaction to food). If you wait until the child is old enough to communicate more effectively, you'll have an easier time figuring out what is going on and treating any problems.
4. Does my family history of allergy/asthma make it more likely that Pumpkin will have a food allergy?
Sadly, yes. All of the reviews and articles I read agreed on this point. There is a strong genetic component to the development of allergies (although it is still not known what genes are involved). She may get lucky and inherit her Daddy's utter lack of allergies, but one depressing study I read about (reviewed in 2) found that all forms of allergic disease are more common in successive generations of a family. This suggests to me that at least some part of the genetic component may show dominant inheritance (i.e., you only need one of your two copies of a gene to be "bad" to show the trait).
5. What other factors might be linked to the development of food allergies?
This was one of the most interesting areas I researched. I was surprised to find that there is a correlation between an allergic mother having a C-section and her baby developing a food allergy, although no link was seen between C-sections and infant food allergies if the mother did not have allergies (reviewed in 1). There is not much you can do about this risk, though, so I just note it as an interesting piece of data.
"High maternal age" was also found to correlate with food allergy (also reviewed in 1), which is also not something I can change at this point, so again, just an interesting piece of data.
One theory I found particularly interesting was that the disturbance of the usual bacterial flora in the intestine by the early use of antibiotics might have a role in the development of allergy. As Bjorksten points out in (1), the flora of the intestine are the largest source of microbial stimulation for the developing immune system. He also references "mounting evidence" that these microbes are required for the development of tolerance to antigens beyond those derived from the bacteria themselves (1). However, a recent study from the Netherlands looked for a link between early exposure to antibiotics (either through direct dosing of the baby or through the breast milk of a mother receiving antibiotics) and food allergy and found no link (5). They did find a link to wheezing, though, and speaking as someone who has suffered a wheezing attack, this is certainly worth avoiding!
Several of the reviews mention a potential role for probiotics (such as Culturelle) in helping to prevent allergies, but indicated that there was no strong evidence on that yet. However, given the study that found a link between early antibiotic use and wheezing, I may look into this further. My pediatrician has already recommended the use of Culturelle in conjunction with any antibiotic course, to minimize the risk of thrush and to help prevent the stomach upset common with antibiotics. Perhaps the Dutch study is indicative of another reason to use probiotics.
Reading all of this suggestive, inconclusive research made me think again about a section in The Omnivore's Dilemma, by Michael Pollan. He writes about how our culture has lost its grounding in what foods are "good to think", i.e., that we no longer have a common, cultural set of food preferences like countries such as Japan and Italy do. In the place of cultural guidance, we have turned to science to tell us what to eat. However, as my research on food allergies illustrates, scientific knowledge is by its very nature incomplete. There will always be something more to learn. So relying on science is a crazy-making way to decide what to eat.
I'm a scientist, and I enjoyed my foray into the literature on avoiding food allergies. However, I know that the information I found is not conclusive. Every article I read pointed out that the data were not particularly conclusive and that more research was needed. So we, as parents, are left to make important decisions about what to feed ourselves and our children with incomplete data. The need to make decisions without all of the "facts" is a common theme in parenting. Therefore, I think relying on science is also a crazy-making way to parent. Once again, the data is always incomplete, and there are too many confounding variables to allow science to give us hard and fast answers on most things. We'd probably all be better off if we erred more towards my Hubby's relaxed "she'll be right, mate" attitude about it all. I am certainly trying to tune into my parenting instinct more.
Personally, I don't miss peanuts enough to add them back into my diet at this point. I think there is a lot to be said for the idea of holding off on the foods that are most likely to cause life-threatening allergic reactions (nuts, peanuts, shellfish) until Pumpkin is old enough to be able to indicate to me that something is not right in a manner more expressive than crying. But I certainly won't judge parents who make different decisions. If a kid turns out to have food allergies, I think that is just bad luck, not evidence of a bad parenting decision. And I'll just hope I never have to find out if I truly believe that.
1. Bjorksten, B. Genetic and environmental risk factors for the development of food allergy. 2005. Curr Opin Allergy Clin immunol, 5:249-253. (PubMed)
2. Sicherer, S. The impact of maternal diets during breastfeeding on the prevention of food allergy. 2002. Curr Opin Allergy Clin immunol, 2:207-210. (PubMed)
3. Vadas, P., Wai, Y., Burks, W., Perelman B. Detection of peanut allergen in breast milk of lactating women. 2001. JAMA, 285: 1746-1748. (PubMed)
4. Greer, F.R., et al. Effects of early nutritional interventions on the development of atopic disease in infants and children: The role of maternal dietary, restriction, breastfeeding, timing of introduction of complementary foods, and hydrolyzed formulas. 2008. Pediatrics, 121:183-191. (This is full article on the new AAP recommendations; PubMed)
5. Kummeling, et al. Early life exposure to antibiotics and the subsequent development of eczema, wheeze, and allergc sensitization in the first 2 years of life: the KOALA birth cohort study. 2007. Pediatrics. 119: 225-231. (PubMed)