Food Related Allergies and Intolerances

Food allergic and intolerance adverse food reactions refer to any abnormal clinical response that occurs following the ingestion of a food or food component other than the nourishment the food is supposed to provide to the body.

These reactions can mainly be divided into two subcategories, immune-mediated food allergies and non-immune-mediated food intolerances, both having different causes and symptoms.

What is a food allergy?

A food allergy is an adverse reaction to foods with the involvement of the immune system. Our immune system protects our bodies with a complex mechanism against harmful elements, such as bacteria, viruses, and toxins. The immune system of allergic people incorrectly identifies certain food constituents as harmful.

The most common type of allergic reaction to food is known as an IgE-mediated response to a food protein. Immune-mediated adverse reactions to foods can affect different organs and systems at the same time. It can cause a range of symptoms, from mild to severe and affect each individual differently. In some cases, an allergic reaction to a food may lead to death. Common symptoms include itching in the mouth, throat or ears, a raised itchy red rash, difficulty swallowing, swelling of the face, around the eyes, lips, tongue and roof of the mouth. In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life threatening. Dietary avoidance of specific allergenic foods in combination with nutritional advice is the mainstay of management in food allergy.

The most common food allergy sources, responsible for up to 90% of IgE-mediated food allergic reactions, particularly in children are: cow’s milk, egg, wheat, soy, tree nuts, peanuts, fish and shellfish (Fig. 1). They are food sources from which many other ingredients are derived. In some cases, the allergenic capacity of some food allergens is destroyed by cooking and food processing, when the proteins are denatured.

Figure 1. Examples of the eight most common food allergy sources (cows’ milk, eggs, wheat, soy, tree nuts, peanuts, fish and shellfish. (Click to expand)

Although the prevalence of food allergies in developed countries is uncertain, the prevalence of food allergies across Europe has been estimated at around 1% for both adults and children (EFSA Journal, 2014, 12, 3894). About 75% of allergic reactions among children are caused by egg, peanut, cows’ milk, fish and nuts. About 50% of allergic reactions among adults are to fruits of the latex group and of the Rosaceae family (which includes apples, pears cherries, raspberries, strawberries and almonds), vegetables of the Apiaceae family (which includes celery, carrots and aromatic herbs) and various nuts and peanuts.

What is a food intolerance?

Food intolerance also triggers an adverse reaction in the body. However, food intolerance reactions do not involve the immune system. Food intolerances are usually related to individual differences in how a person digests, absorbs, or metabolizes a food. In general, although they can negatively impact our health, symptoms of food intolerance are usually less severe. This adverse reaction to a food usually takes place within the gastrointestinal tract. People with food intolerance may have symptoms such as diarrhea, bloating, nausea, constipation and stomach cramps. Typically, symptoms of food intolerance may not be as immediate as in food allergy (20min-48h after eating).

A wide variety of foods are associated with food intolerance. The most frequently encountered include milk (lactose intolerance) and several cereal products (gluten intolerance). In lactose intolerance, for example, the body is unable to digest lactose, the main carbohydrate in milk. This occurs due to insufficiency of the lactase enzyme present in the intestine, which is needed to break down lactose into glucose and galactose. Ingestion of lactose containing products leads to alteration in intestinal digestion and colonic fermentation, leading to adverse gastrointestinal symptoms, such as gas, bloating, and diarrhea, about 30 min to 2 h after ingesting dairy products containing lactose. For lactose intolerant people, it is nowadays not necessary to avoid the nutritional value of dairy products. There’s a complete range of products in the market offering lactose-free whole milk, skim milk, cream, and other varieties. These products are able to provide the essential nutrients present in regular dairy products, like calcium and vitamins, to those that are not able to digest lactose. To do this, manufacturers add an enzyme called lactase during milk processing.

Figure 2. Lactose digestion in the intestine (Click to expand)

There are examples of food intolerances other than lactose, for instance, gluten intolerance, also called non-celiac gluten sensitivity (NCGS). Gluten is a general name for the proteins found in wheat, rye, barley and triticale (a cross between wheat and rye). If a person has gluten intolerance, this protein can cause digestive problems such as gassiness, abdominal pain or diarrhea. It should be emphasized that gluten intolerance should not be confused with Celiac disease (CD); the latter is an autoimmune disorder that is triggered by ingestion of gluten. Unfortunately, unlike CD, there are no specific medical tests that can be performed to confirm NCGS diagnosis; this is done when both CD and wheat allergy have been ruled out.

Other adverse reactions to foods or beverages, such as chocolate, ripened cheese, red wine, and even ice cream trigger headaches in some individuals. Food additives, including sulfite, nitrate and nitrite preservatives, certain food colorants, the flavor enhancer monosodium glutamate, may also cause reactions in susceptible people.