Does introducing solids early cause food allergies?
A recent scientific publication in the journal Pediatrics examined the eating behavior and health records of about 1000 infants from birth to 5 years of age. They examined the type of foods that were fed to babies (such as potatoes, oats, rye, wheat, meat, fish and eggs) and when they first were exposed to each food. They used these data points to predict each baby's sensitivity to foods by measuring what is called allergen-specific immunoglobulin E (IgE). The authors found that babies who had a late introduction of oats (after 5 months of age) or eggs (after 10.5 months of age) were more likely to develop allergies to other foods such as cow's milk and eggs. They found the same results with potatoes (after 4 months of age), rye (after 7 months of age), wheat (after 6 months of age), meat (after 5 and a half months of age), and fish (after about 8 months of age).
The authors also found that the late introduction of potatoes, rye, meat and fish increased baby's risk of developing what are called inhalant allergies later in life. Inhalant allergies are when your body has an allergic reaction (such as difficulty breathing, nasal irritation, or runny nose) to something you inhale; the most common inhalant allergies are to dust, pollen, grasses, trees, flowers and pet dander.
All of these effects persisted even when the authors corrected for over a dozen factors that might predict allergies, such as whether the parents have allergies or asthma, or whether the babies were breast or bottle fed. They also were able to rule out the possibility that these effects were due to parents delaying food introduction due to higher perceived risk of their baby developing allergies. That is, parents sometimes will delay the introduction of solids because they fear that their baby might have an allergy, usually because they or a close relative has a food allergy; this kind of behavior can make it look like the later introduction of solids leads to higher rates of eventual food allergies. In this study, this was not the case.
Overall, these results converge with a growing body of evidence demonstrating that the delayed introduction of solid foods not only doesn't decrease the risk of food allergies but might actually increase the risk. Many modern guidelines suggest exclusively breastfeeding a baby until they are at least 6 months of age, but this work suggests that these guidelines may have limited or no scientific basis.
Nwaru, B. I., Erkkola, M., Ahonen, S., Kaila, M., Haapala, A.-M., Kronberg-Kippila, C., Salmelin, R., Veijola, R., Ilonen, J., Simell, O., Knip, M., & Virtanen, S. M. (2010). Age at the introduction of solid foods during the first year and allergic sensitization at age 5 years. Pediatrics, 125, 50-59.