Can allergies be prevented? A question that triggers much debate, to be sure.
In recent years, well-meaning parents have delayed the introduction of common allergens, such as eggs and nuts, sometimes beyond the first year of life, and women have nixed peanut butter during pregnancy, all in the hopes of reducing the risk of their children developing allergies, asthma and eczema. But recent guidelines, published by the American Academy of Pediatrics and the European Society of Pediatric Gastroenterology, Hepatology and Nutrition, deemed these practices ineffective at preventing allergies. Since then, even newer evidence has suggested that the now three-year-old guidelines themselves might need some revising.
So how does maternal and early childhood diet influence allergy risk in children? While there is still much to learn, here is what we know - for now.
Preventing allergies: The current guidelines
The two newest guidelines on the prevention of allergies in infants and children, both published in 2008, included several key consensus points. Among them: Whenever possible, infants should be breastfed exclusively until about six months of age; solid foods (also known as complementary feeding) should not be introduced before 17 weeks; all infants should start complementary feeding by 26 weeks.
Aside from these points, there was no recommendation to delay or avoid the introduction of common allergens, such as eggs or nuts. The guidelines did not make any recommendations about what pregnant mothers should or should not eat to reduce the risk of allergy for their infants.
Preventing allergies: The new evidence
The current edition of the American Journal of Clinical Nutrition includes a review of two newer, largescale studies on allergy development. Known as GINIplus (German Infant Nutrition Intervention Program; the "plus" refers to air pollution and genetics) and LISAplus (Influence of Lifestyle-related Factors on the Development of the Immune System and Allergic Diseases), the two studies enrolled a combined 9,088 infants from various parts of Ger-many between 1995 and 1999. From the initial group, a sub group of 2,252 infants with a family history of allergies were enrolled in a trial to examine how variations in their early diets influenced their risk of developing allergies, asthma and eczema.
Consistent with the 2008 guidelines, the data available thus far from GINIplus and LISAplus suggests that babies who were breastfed are at a significantly lower risk of being diagnosed with eczema later in childhood. The researchers also found that delaying the introduction of solids past six months, or avoiding highly allergenic foods during the first year, did not protect against the development of allergy, asthma or eczema.
Unlike the current guidelines, however, the two studies did find a link between the mother's diet and allergy risk in the infant. In particular, mothers who consumed a large amount of margarine, vegetable oils and some allergenic fruit (citrus fruits in particular) and vegetables (raw sweet peppers and celery) during pregnancy were more likely to have children with allergies or eczema. Conversely, consuming fish during pregnancy seems to protect against allergy. And perhaps most notably, the combined results of both studies did not demonstrate any link between consumption of nuts during pregnancy and allergy risk in children. (Peanut butter-loving mothers everywhere can rejoice!)
What to make of the findings?
Before pregnant women everywhere start cutting oranges out of their diet, however, it is important to realize that the findings about the consumption of margarines, vegetable oils and certain fruits and vegetables during pregnancy is relatively new, and fall outside of the current guidelines. Having said that, the authors reasoned that margarines and vegetable oils could plausibly trigger allergy because of their rich omega-6 fatty acid content.
Known for their ability to trigger inflammation, a diet high in omega-6 fatty acids and low in antiinflammatory omega-3 fatty acids has been theorized to play a role in the development of a number of medical conditions. Conversely, consumption of fish, one of the richest sources of omega-3 fatty acids, could have the reverse effect, which could explain the protective effect observed for women who ate fish regularly during pregnancy.
New findings aside, it is worth remembering that there is much more research to be conducted in the area (the two studies followed the children until age 10, but only the data up to age six has been published thus far), and there are many nondietary factors that could influence allergy risk.
But the new results provide even more convincing evidence that avoiding common allergens in the diet of young infants does not seem to protect against the development of allergies in children, at least up to six years of age.
We also have good evidence that the optimal window to introduce solids ranges between four and six months of age, but waiting any longer does not seem to be beneficial. Prior to four months of age, breastfeeding seems to be the best way to reduce the risk of allergy, or at the very least, eczema.
Jennifer Sygo is a registered dietitian at Cleveland Clinic Canada, which offers executive physicals, sports medicine and prevention and wellness counselling in Toronto.