Differences Between Food Intolerances and Food Allergies

There is considerable ambiguity around the terms “food allergy” and “food intolerance.” People tend to use “food allergy” when referring to immediate hypersensitivity reactions, which produce the classic symptoms of allergy (e.g. hives, asthma, eczema, etc). Many use “food intolerance” when referring to delayed, type III hypersensitivity reactions to food. In the latter case, symptoms show up hours or days after food ingestion and are often vague or not commonly associated with allergy (e.g. irritable bowel syndrome, migraine, depression, fatigue, “sick all over” feeling).

Food Allergy = Immune-Mediated Hypersensitivity

Allergy refers to a hypersensitivity that involves a heightened response in the immune system. The substance causing the response is called an allergen and can come from a wide range of sources, including animal dander, dust, pollen, volatile chemicals, or foods. The word allergy originally meant, “altered reactivity.” Later, the definition of allergy became narrowed down to mean an immediate immune response to a substance.

Food Hypersensitivy = Food Allergy

Not everyone was happy with this narrow definition of food allergy because certain foods cause a delayed reaction which many physicians referred to as “delayed” or “masked” food allergy. Eventually, the term hypersensitivity was adopted to describe all forms of responses that involve the immune system. In the 1960s, Gell and Coombs described four types of hypersensitivity, listed below. Hypersensitivity to foods is almost always restricted to type I or type III mechanisms.

Type I (called also immediate hypersensitivity) involves cell-fixed antibodies, mainly IgE attached to mast cells or basophils. Antigen binding causes the cell to release vasoactive factors. The basis for anaphylaxis and atopy.
Type II causes cell destruction (cytotoxicity) by the action of immunoglobulin with complement or cytotoxic cells. Seen in red blood cell transfusion reactions and in alloimmune hemolytic anemia. See also antibody-dependent cellular cytotoxicity.
Type III (called also immune-complex or subacute hypersensitivity) causes tissue damage and inflammation by the deposition of antigen-antibody complexes that activate complement and attract polymorphonuclear cells.
Type IV (called also delayed hypersensitivity) involves sensitized T-lymphocytes that react with cell-bound or associated antigen. Lymphokines are released causing mononuclear cell accumulation, tissue damage and inflammation, typically manifesting at least 24 hours after exposure to the antigen.

Type I Hypersensitivity is Mediated by IgE Antibodies

The IgE-mediated immune response evolved to deal with foreign agents with potentially harmful properties to the body. Most parasitic worms and certain protozoan parasites evoke an IgE-mediated response. Normally, food molecules are recognized by the immune system as “harmless” and allowed entry into the body. This process begins in infancy and is called immune tolerance. But in a type I food allergy, the food molecule – usually a protein – is recognized by the immune system as “foreign” and IgE antibodies to that protein, now called an antigen or allergen, are created. These IgE antibodies attach themselves to mast cells that contain granules filled with powerful inflammatory mediators, such as histamine and cytokines. The next time that food allergen is ingested, it binds to these mast cell-bound IgE antibodies, setting off a degranulation process: the mast cell releases its inflammatory chemicals into the surrounding environment and a full blown inflammatory response occurs. The symptoms of type I allergy include but are not limited to:

Skin: Redness, swelling (edema), itching, rash, hives
Respiratory tract: excess mucous production, edema, coughing, wheezing, shortness of breath, rhinitis, sneezing, bronchospasm
Eyes: edema below the eyes (allergic “shiners”), redness, itching
Gut: indigestion, gas, bloating, diarrhea, vomiting, cramps

Type III Hypersensitivity is Mediated by IgG Antibodies

Normally, the lining of intestinal tract prevents the absorption of food molecules that have not been sufficiently broken down through digestion. This is called the gut barrier. But an inflammatory reaction in the gut can cause a “leaky gut sydrome” that weakens the gut barrier, potentially allowing insufficiently digested food molecules to enter the gut mucosa and bloodstream. Here, they can bind with IgG antibodies to form immune complexes that can circulate throughout the body and cause an inflammatory response. Type III hypersensitivity can affect any system in the body and produce a plethora of symptoms, including irritable bowel syndrome, migraine, depression, fatigue, and a malaise often described by patients as a “sick all over” feeling.

Food Intolerance = Food Sensitivity

Food intolerance is often called “non-allergic food sensitivity” and is generally reserved for adverse reactions to food that do not involve the immune system. About 10% of people experience adverse reactions to specific foods, which are often chronic and may cause severe illness. Food intolerance is not synonymous with food allergy.

The mechanisms of food intolerance are many and varied and include:

Metabolic reactions:

inability to tolerate milk due to lactose defiency
adverse response to simple carbohydrates in diabetes
phenylketonuria (inability to metabolize the amino acid phenylalanine)
hereditary fructose intolerance

Pharmacological or toxic reactions

Reactions to certain food molecules such as caffeine, histamine, salicylates, amines, and sulphites
Reactions to food additives such as food colorings or monosodium glutamate
gluten intolerance (as opposed to celiac disease which is an immune-mediated

Conclusion

To summarize, the terms food allergy and food hypersensitivity refer to immune-mediated food reactions. The vast majority of food allergy symptoms involve either a type I or type III hypersensitivity mechanism. Food intolerance refers to a non-immune-mediated adverse reaction to food.

Diagnosing and eliminating foods that one may be intolerant to can be a long, painstaking process because there is no known test to detect them with 100% accuracy. The gold standard for treating food hypersensitivity and intolerance is the elimination diet, which removes suspected offending foods from the diet until symptoms subside and then reintroducing them one by one and observing the response. If a patient presents with symptoms of delayed food allergy, such as irritable bowel syndrome, migraine, depression, fatigue, joint pain, and malaise, the Imupro food allergy IgG blood test can identify which foods may be causing them. The kit provided by LSIA comes in three versions, depending on the number of foods tested: Imupro 100, 200, and 300.