Allergenic Food Proteins

Updated: May 2003

Article Summary

Food allergy is caused by specific food proteins. Large proteins trigger the immune system. If a protein is broken down during digestion or by heat treatment, it would be too small to trigger an allergic reaction.

What are Food Proteins?

Food is made of many components such as, protein, fat, water, carbohydrate (sugar and starch), vitamins and minerals. Protein is the component of food that triggers an allergic reaction. Each food has many different proteins. For example, cow’s milk has more than 15 different proteins.

Amino acids are the building blocks of protein. If a protein were a pearl necklace, the amino acids would be individual pearls. There are 20 different amino acids. The type and sequence of amino acids determines the nature of the protein. Each protein in milk has a unique amino acid composition and sequence.

What food proteins trigger an allergic reaction?

During an allergic reaction, the immune system reacts to a specific protein in the food. The protein triggers the formation and activation of antibodies against that food.

Large food proteins activate the immune system. In other words, the pearl necklace must be very long. If the protein is small, the immune system will ignore it and an allergic reaction will not occur. In Food Allergies, the immune system was compared to an army. An army would not launch an attack against a small enemy.

Why is the digestive system important in food allergy?

The ability to digest protein is a critical factor in the potential for an allergic reaction. As explained in Digestive System, food proteins are broken into individual amino acids during digestion Individual amino acids are very small. Amino acids are ignored by the immune system and do not trigger a reaction.

Food allergy is more common in young infants than in adults. There are many factors that contribute to this. One reason is that young infants have an immature digestive system. The immature digestive system does not break protein down as efficiently as an adult’s digestive system. Therefore, large food proteins are left and can trigger an allergic reaction. Regular infant formulas contain large food proteins. Infants that are allergic to regular infant formula will often tolerate special formulas that have been treated to break the food proteins into individual amino acids. As the digestive system matures, protein digestion improves and many infants lose their food allergies.

Does heating affect the allergic potential of a food?

Some food proteins break apart when heated. Other proteins do not. If a protein breaks apart, it will no longer cause a food allergy.

Animal food proteins (such as egg, milk, meat) are heat stable, and cooking does not reduce the allergic potential of these foods. On the other hand, most proteins in fruit and vegetables will break down when heated. Many people that are allergic to raw fruit and vegetables tolerate them cooked.

What is cross reactivity?

Cross reactivity happens when an individual is allergic to two different substances because they have similar proteins.

Examples of cross reactivity include:

	Cow’s milk and goat’s milk- the proteins in these milks are similar. Most individuals with a cow’s milk allergy also react to goat’s milk.
	Gluten – gluten is protein found in wheat, rye, barley and oats. Individuals with gluten allergy must avoid all four grains.
	Latex and food allergy – the allergic protein in latex is very similar to proteins in some fruit and vegetables. Individuals with latex allergy are more likely to have and allergy to these fruit and vegetables.