Is there anything that you should not eat while pregnant or nursing?

This is an interesting question that I have seen pop up quite frequently on some of the pregnancy message boards that I frequent.  According to the American Academy of Pediatrics (AAP) revised policies published in January 2008, "current evidence does not support a major role for maternal dietary restrictions during pregnancy or lactation" for mothers of children that are not at "high risk of developing allergy (ie, infants with at least 1 first-degree relative [parent or sibling] with allergic disease)."

When reading the policy, the AAP defines "atopic disease" as "clinical disease characterized by atopy; typically refers to atopic dermatitis, asthma, allergic rhinitis, and food allergy."

The AAP summarizes their findings based on available data below:

1. At the present time, there is lack of evidence that maternal dietary restrictions during pregnancy play a significant role in the prevention of atopic disease in infants. Similarly, antigen avoidance during lactation does not prevent atopic disease, with the possible exception of atopic eczema, although more data are needed to substantiate this conclusion.
2. For infants at high risk of developing atopic disease, there is evidence that exclusive breastfeeding for at least 4 months compared with feeding intact cow milk protein formula decreases the cumulative incidence of atopic dermatitis and cow milk allergy in the first 2 years of life.
3. There is evidence that exclusive breastfeeding for at least 3 months protects against wheezing in early life. However, in infants at risk of developing atopic disease, the current evidence that exclusive breastfeeding protects against allergic asthma occurring beyond 6 years of age is not convincing.  
4. In studies of infants at high risk of developing atopic disease who are not breastfed exclusively for 4 to 6 months or are formula fed, there is modest evidence that atopic dermatitis may be delayed or prevented by the use of extensively or partially hydrolyzed formulas, compared with cow milk formula, in early childhood. Comparative studies of the various hydrolyzed formulas have also indicated that not all formulas have the same protective benefit. Extensively hydrolyzed formulas may be more effective than partially hydrolyzed in the prevention of atopic disease. In addition, more research is needed to determine whether these benefits extend into late childhood and adolescence. The higher cost of the hydrolyzed formulas must be considered in any decision-making process for their use. To date, the use of amino acid–based formulas for atopy prevention has not been studied.
5. There is no convincing evidence for the use of soy-based infant formula for the purpose of allergy prevention.
6. Although solid foods should not be introduced before 4 to 6 months of age, there is no current convincing evidence that delaying their introduction beyond this period has a significant protective effect on the development of atopic disease regardless of whether infants are fed cow milk protein formula or human milk. This includes delaying the introduction of foods that are considered to be highly allergic, such as fish, eggs, and foods containing peanut protein.
7. For infants after 4 to 6 months of age, there are insufficient data to support a protective effect of any dietary intervention for the development of atopic disease.
8. Additional studies are needed to document the long-term effect of dietary interventions in infancy to prevent atopic disease, especially in children older than 4 years and in adults.
9. This document describes means to prevent or delay atopic diseases through dietary changes. For a child who has developed an atopic disease that may be precipitated or exacerbated by ingested proteins (via human milk, infant formula, or specific complementary foods), treatment may require specific identification and restriction of causal food proteins. This topic was not reviewed in this document.

With this revision, the AAP is stating that unless a child is at high risk for developing an allergy, there is no restriction as to what a mother can eat while pregnant or breastfeeding.  If a child is at high risk, exclusive breastfeeding (with no formula supplementation) for at least 4 months decreases the risk of developing atopic dermatitis (eczema) and an allergy to cow's milk.  For all children, breastfeeding for at least three months may protect against wheezing in early life.  If a child is at high risk for developing an allergy and is not exclusively breastfed, there is some evidence that eczema may be delayed or prevented by using extensively hydrolyzed formulas compared with cow milk formula in early childhood.  There is no evidence for the use of soy-based formula for the purpose of allergy prevention.  Solid foods should not be introduced before 4-6 months of age.  Furthermore, delaying introduction of solid foods after 6 months does not offer more protection against the development of allergies regardless if a baby has been fed formula or breastmilk.  Also, there is no evidence that delaying the introduction of foods such as fish, eggs or peanuts will protect against the development of allergies to those foods.