Food Allergies - Avoidance Diets

Typically, the prevention of IgE-mediated food allergies primarily involves avoiding the offending foods. Certain drugs, such as epinephrine (adrenaline) and various anti-histamines, can be used to treat the symptoms that develop during an allergic reaction if inadvertent ingestion of the offending food occurs.

However, no pharmaceutical approaches are presently available for the prevention of food allergies. Anti-IgE therapy may hold some promise as initial trials have resulted in an increase in tolerance to peanuts among peanutallergic individuals.

With the lack of pharmaceutical approaches, specific avoidance diets remain the preventive strategy of choice for most food-allergic individuals. Thus, food-allergic individuals are forced to become avid label readers in an attempt to avoid their offending foods and certain ingredients derived from these foods.

Their efforts are fraught with difficulty because individuals with IgEmediated food allergies can react to mere traces of the offending food in their diet. The construction of safe and effective avoidance diets and the difficulties faced by consumers who must adhere to such diets have been extensively reviewed elsewhere.

Consumers with IgE-mediated food allergies often face several challenging questions as they attempt to implement a safe and effective avoidance diet.

  1. Will trace levels of the food elicit reactions or increase sensitization?
  2. Do all foods and food ingredients made from the offending food contain the allergens?
  3. Are cross-reactions likely to occur between closely related species?

Clear answers to these questions are not always available, in part because of a lack of research data and in part because of the lack of reliable analytical information.

For example, many ingredients are derived from commonly allergenic foods; soybeans alone are used to generate hydrolyzed soy protein, soy sauce, soy oil, soy lecithin, soy isoflavones, tocopherol (vitamin E), soy phytosterols, soy fiber, and others.

Not all of these ingredients will be expected to contain the responsible allergens but clinical data on safety are often lacking. Also, from an analytical perspective, detection of proteins or allergens can be particularly challenging in some of these ingredient matrices. For example, the detection of protein residues in oils can be difficult.

Until recent years, reliable methods for the detection of residues of allergenic foods in other foods or in such ingredients did not exist. Even now, the ability of existing methods to assess the allergenic potential of ingredients containing hydrolyzed or partially hydrolyzed proteins is problematic.

Practical experiences indicate very clearly that trace levels of the offending food can elicit adverse reactions. Anecdotal reports exist of reactions from:

  • touching utensils or bottles contaminated with the offending food
  • kissing the lips of someone who has recently eaten the offending food
  • opening packages of the offending food
  • the inhalation of vapors from cooking of the offending food
  • and the transfer of food allergens from lactating mothers to breast-feeding infants.

Although the amount of the offending allergen involved in eliciting such reactions must be rather low, analytical information on minimal eliciting doses from such experiences is not available. However, a few episodes of reactions to residues of allergenic foods hidden in other foods have been well investigated and lend credibility to the anecdotal reports.

For all practical purposes, complete avoidance must be maintained. Analytical evidence can be used, in part, to obtain clues to the minimal eliciting doses for various allergenic foods. However, great care must be taken in the use of this information to establish such doses.

First of all, existing evidence suggests that food-allergic individuals may vary in their minimal eliciting doses by several orders of magnitude. This fact complicates the investigation of case reports because the affected individual will not necessarily be representative of other individuals in the population allergic to the same food.

A second uncertainty factor surrounds whether or not a representative food sample can be obtained for analysis. On many occasions, several foods are consumed, and the affected consumer may not necessarily incriminate the food that actually caused the reaction. If the analyst finds a very low level of allergenic residue in an incriminated food.

It is very important to determine if this food was the only one consumed at the implicated meal because other foods might have even higher levels of the particular allergen. Additionally, the consumer may have consumed all of the incriminated food sample or discarded the remainder.

In those situations, the analyst can attempt to obtain similar samples from the marketplace, but the analysis of these samples creates uncertainties due to the questions about whether this sample is representative of the actual product that may have caused the illness.

Analysis of samples from actual episodes is always complicated if the allergen contamination may not have been uniform. The bite that the consumer eats may have higher levels of allergen contamination than the remaining portion in some cases.

Finally, until recently, reliable analytical methods for the detection of residues of allergenic foods were not readily available. Even today, it is uncertain whether analysis of the same sample by several different methods would yield a similar result.

When assembling data from the existing literature, the analytical results presented in case reports may be somewhat questionable and direct comparison with results from current methods may be difficult. Despite uncertainties involved in the investigation of consumer complaints.

Threshold doses or minimal eliciting doses do exist below which allergic individuals will not experience adverse reactions. These minimal eliciting doses are likely to be very low and variable from one allergic individual to another. For example, the minimal eliciting doses for peanut needed to provoke mild.

Objective adverse reactions in one particular group of peanutallergic individuals ranged from 2 to over 50 mg. Although a rather large number of low-dose challenge trials have now been conducted for peanut, milk, and egg in particular, consensus does not yet exist on the minimal eliciting dose for the most sensitive individuals.

For example, other investigators have occasionally identified individuals with lower minimal eliciting doses than 2 mg. While consensus on minimal eliciting doses has not been achieved, dose-response modeling for peanut, milk, and egg indicate that only 1% or less of the affected population would react to residual levels of the allergenic food of 0.26 mg for egg, 0.76 mg for peanut, and 7.76 mg for milk.

Additional controlled challenge studies conducted with standard challenge protocols will likely reduce the uncertainty of these estimates in coming years. Existing test methods for residues of allergenic foods appear to be in the ideal range to detect potentially hazardous residues of undeclared allergens in foods.

Current immunoassay methods have lower limits of about 1 ppm (1 mg/kg). If minimal eliciting doses are 200 μg or higher and typical serving sizes are 50–100 g or less, then potentially hazardous foods would be easily detected with these immunoassay methods.

If a highly sensitive individual ingested a typical 50 g serving of a food containing 200 μg of undeclared residues of an allergenic food, that food would have contained 4 ppm of the offending food. Previously, the advice given was that foods containing less than 10 ppm of undeclared residues of an allergic food would present little risk to food-allergic consumers.

That advice remains fairly sound now that much more evidence exists on minimal eliciting doses. The development of analytical procedures that are more sensitive than the current ones does not seem to be justified.

Food-allergic consumers, especially those susceptible to comparatively low threshold levels, can occasionally experience reactions to packaged food products even when the ingredient list indicates that the particular item should be safe.

In manufacturing situations, foods may become contaminated with trace amounts of other foods through various means including the use of rework and the use of shared equipment. No avoidance diet provides absolute safety, but careful adherence to an effective avoidance diet will minimize the chances of a reaction.