Tree Nuts and Food Allergy Basics

Table of Contents

  1. Introduction
  2. What is a food allergy
  3. Sensitizing to allergens
  4. Common symptoms of an allergic reaction
  5. Severe symptoms of an allergic reaction
  6. Sensitivity to allergens
  7. Related links


Tree nuts are a nutritious food and a good source of protein. There is ongoing interest by a small yet dedicated group of growers to develop commercial and hobby tree nut industries in Ontario, (e.g. the Society of Ontario Nut Growers and the Northern Nut Growers Association. Many people enjoy high quality tree nuts that are grown in our temperate climate of southern Ontario.

Tree nuts represent a food group that is unique from other typical farm crops in that they are healthy to most people. However, to a small percentage of the population, tree nuts pose a serious health threat. Approximately 2.5% of the population in North America have allergic reactions to specific foods, while as many as 25% of the same population 'believe' they have allergy to various foods.

Figure 1. Native black walnut orchard cultivar (left). English walnut cultivar (right). Each plate displays the total kernels from 10 average-sized walnuts.

A picture of native black walnut orchard cultivar on the left and english walnut cultivar on the right.

The fact that tree nuts contain certain proteins that are allergenic to a low percentage of the population requires that tree nuts be handled with very special precautions for the benefit of sensitive consumers. Precautions need to begin right at the farm and continue right to the market. This is particularly important where farmers are involved in the production and labeling of value-added products that may contain tree nuts.

An understanding of allergic reaction is also important where farmers grow tree nuts in addition to other non-nut foods. Separation of tree nuts and all equipment that is dedicated specifically to tree nut production is very important to achieve food safety.

Consumers who suffer with the threat of allergic reactions depend entirely on accurate ingredient labels found on food packaging. Food processors that use raw food ingredients from farms or from co-manufacture suppliers must know that raw products are free of allergens (or are known to contain food allergens), to ensure their product ingredient labels are fully reliable.

Try to imagine the extreme difficulties imposed upon not only the allergenic consumer, but also their family and friends in trying to achieve 'total exclusion' of food allergens. People with food allergies depend entirely on food labels with accurate ingredient declarations to enable them to determine how safe the food is to eat.

What is a food allergy

A true food allergy is a response where the body's immune system overreacts to the protein portion of a normal food, for example, the proteins found in peanuts or tree nuts. The allergic reaction produces unpleasant symptoms for some people and sometimes life-threatening symptoms for others. Allergic reactions are different from other food sensitivities or intolerance, such as lactose intolerance. An allergy involves the immune system while intolerance to specific food does not involve the immune system.

Sensitizing to allergens

When a food-allergic individual is first exposed to a food that their body mistakenly believes is harmful, it will develop specific immunoglobulin antibodies to help fight the invading food protein. In a normal immune system the body does this in an attempt to protect itself against disease cells.

The immunoglobulin then attaches to the surface of mast cells in the body. A mast cell is a type of cell containing histamine and occurs in all body tissue but is especially prominent in the nose, throat, lungs, skin and gastrointestinal tract, body sites that are typical of allergic reactions. In a normal immune system the immunoglobulin would be attaching to the surface of disease cells, not mast cells. The sensitizing exposure is complete.

After sensitizing, the immunoglobulin-mast cell complex builds up in the body. During this buildup the person does not experience any allergic symptoms, not until the next time they are exposed to the same food protein. Therefore, the first exposure does not cause an allergic reaction.

The next time the body is exposed to the food protein, a destructive 'domino effect' is triggered. The mast cells are destroyed by the immune system, releasing massive amounts of histamine and other chemicals within the body. In a normal immune system, this releasing effect would be welcome because disease cells would be destroyed in the process.

The released histamine and other chemicals trigger a cascade of allergic symptoms in the body that can affect the - respiratory system, gastrointestinal tract, skin and cardiovascular system.

Common symptoms of an allergic reaction

Different people have different sensitivities to food allergens and the resulting reactions can range from mild to severe. These include itching, skin rashes (hives), breathing problems, swelling and puffiness especially to mucous membranes.

Severe symptoms of an allergic reaction

Anaphylaxis (anna-phil-ax-is) or anaphylactic shock, the most serious reaction, can cause a dangerous drop in blood pressure and a change in the heart's rhythm which, when they exist in combination, may cause death without immediate attention.

Sensitivity to allergens

Different people have different sensitivities to allergens:

  • by the amount of allergen that triggers a response
  • by having allergenicity to more than one allergen
  • Any food with protein has the potential to cause allergic reaction. Ten food groups account for 90% of all food-allergic reactions including tree nuts, peanuts, milk, eggs, shellfish, fish, soybeans, wheat, sesame seeds, mustard plant family (see note below), and sulphite additives greater than 10 ppm

According to one study, tree nuts and peanuts appear to account for more than 90% of food allergic deaths in North America. Unfortunately, there are currently no cures for food allergies.

Therefore, the only way a consumer can prevent a reaction is to avoid foods that contain a given allergen. After suspected ingestion of a food allergen, epinephrine injection (or adrenaline) can be administered to counter some of the released histamine, giving the victim time to get to a hospital for proper treatment.

Note on Mustard: Mustard belongs to the Brassicaceae family, which includes other members such as broccoli, cauliflower, cabbage, Brussel sprouts, turnip and rapeseed. Since these plants are closely related to mustard, their seeds contain very similar proteins to mustard seeds. People with mustard allergy should avoid consuming the seeds and sprouted seeds of other members of the Brassicaeae family as these have the potential to trigger an adverse reaction. While some people with mustard allergy have reported reactions to plants in the Brassicaeae family, such as cabbage or cauliflower, the protein in mustard seed that triggers allergic reactions is a specific seed storage protein that is not found in mature plants. (Reference: Health Canada 2012).

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