Intolerance is the more general term for any negative response by the body to a particular food or food additive, whereas a food allergy is far more dangerous and refers specifically to situations when the body launches an immune system attack against a substance. While there is an adverse reaction in the body in cases of both allergy and intolerance, their causes and symptoms tend to be significantly different.

Allergies can be to food, medication, animal fur or insect stings, and environmental factors like pollen or dust. This comparison refers specifically to food allergies and food intolerance.

Comparison chart

Food Allergy versus Food Intolerance comparison chart
Edit this comparison chartFood AllergyFood Intolerance
Introduction A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions. A negative physiological response associated with a particular food or compound found in a range of foods. Also known as (non-allergic food hypersensitivity).
Physiology Immune system treats proteins in food as foreign bodies and attacks them. Body can't properly digest or absorb the nutrients of a food product.
Symptoms Hives, itching, swelling of throat, runny nose, itchy, watery eyes, hoarse voice, wheezing, nausea, vomiting, abdominal pain, lightheadedness, fainting, death. Abdominal cramps, nausea, diarrhea, constipation, irritable bowel syndrome, rashes, eczema, dermatitis, sinusitis, asthma, unproductive coughs
Common Causes Peanuts, pecans, pistachios, pine nuts, walnuts, coconuts, sesame seeds, poppy seeds, milk, eggs, seafood, shellfish, soy, wheat Lactose, food chemicals like salicylate, tartrazine, benzoic acid, and other food additives and preservatives.
Diagnostic Test Skin prick, blood test, food challenge Hydrogen breath testing, elimination diets, food challenge
Reaction Types Immunological Immunological, pharmacological, gastro-intestinal, metabolic, psychosomatic, toxic
Reaction Time A few seconds to 1 hour 30 min - 48 hours
Prevention Avoidance, breastfeeding, nutrient supplementation Avoidance
Management Avoidance, epinephrine, antihistamines, steroids. Avoidance, elimination diets
Prevalence 2-20% of population 6-8% of children under age 3, 4% of adults
ICD-10 T78.0 K90.4-Z71.3
ICD-9 V15.01-V15.05 V69.1

Definition

What is food allergy?

Distinct from other adverse food reactions like food intolerance, pharmacological, and toxin-mediated reactions, a true food allergy only occurs when a body's immune system mistakenly identifies a food protein as harmful and attacks it. To be considered a food allergy, a reaction requires the presence of immune mechanisms (for instance Immunoglobin E - IgE antibodies) against the food.

What is food intolerance?

Food intolerance is a merely delayed detrimental reaction (say, indigestion) to a food substance - it may produces symptoms in one or more body organs and systems, but does not give an immediate violent reaction like true food allergy would.

A closer look at food allergy and intolerance:

Common Causes

Food allergies are most commonly caused by proteins found in milk, eggs, peanuts, tree nuts, seafood, shellfish, soy, and wheat. Also, seeds like sesame and poppy include oils which sometimes contain allergenic proteins. Egg allergies are also common in that they affect about one in fifty children, but are frequently outgrown by children when they reach the age of five. Typically the sensitivity is to proteins in the white, rather than the yolk. Milk of all varieties is another common food allergen, and many sufferers are unable to tolerate dairy products like cheese. About 10% of children with a milk allergy are likely have a reaction to beef. Beef contains a small amount of protein that is present in cow's milk.

Intolerance often results from chemical components of the diet, such as various organic chemicals occurring naturally in a wide variety of foods, both of animal and plant origin, more often than to food additives, preservatives, colorings and flavorings, such as sulfites or dyes, though these are also common. The most common naturally occurring chemicals are salicylates and benzoates. Other commonly reactive chemicals include amines, nitrates, sulphites and some antioxidants. Benzoates and salicylates occur naturally in many different foods, including fruits, vegetables, juices, spices, herbs, nuts, wines, coffee and tea. A deficiency in digestive enzymes can also cause some types of food intolerances, such as lactose intolerance, which is a result of the body not producing sufficient lactase to digest the lactose in dairy foods.

Diagnosis

In order to diagnose a food allergy, an allergist will review the patient's history and the symptoms or reactions that have been noted after food ingestion and perform allergy tests if necessary. Tests include skin prick tests, blood tests, and food challenges. In a skin prick test, a board covered in protruding needles with an allergen on them will lightly puncture an individual's skin to see if a hive is produced. This test and blood tests only work for lgE antibody related reactions. A food challenge is a more direct method where a person is given a pill containing an allergen and watched for symptoms.

A diagnosis for food intolerance is made using medical history and cutaneous and serological tests to exclude other causes, but to obtain final confirmation a controlled food challenge must be performed where the patient is given the allergen and watched for symptoms. Other methods include hydrogen breath testing, which is used for lactose intolerance and fructose malabsorption, and professionally supervised elimination diets, where an individual must remove all poorly tolerated foods, or all foods containing offending compounds.

Symptoms

Allergic reactions can range from mild to severe, and include symptoms such as hives, itching, swelling of throat, runny nose, hoarse voice, wheezing, nausea, vomiting, abdominal pain, lightheadedness, fainting, and even, in some serious cases, death. A common term used with severe allergic reactions is anaphylaxis, which is a term used for situations where the body's immune response goes so far as to make the throat swell where it becomes difficult to breathe and blood pressure often lowers to dangerous levels.

An intolerance often results in similar symptoms to an allergic reaction, though often less severe in scope, and may include abdominal cramps, nausea, diarrhea, constipation, irritable bowel syndrome, rashes, eczema, dermatitis, sinusitis, asthma, unproductive coughs. Because many intolerances are digestion-related, those symptoms relating to the digestive tract are very common.

Reaction Types

Though food allergies only produce immunological reactions by definition, food intolerances display themselves in a variety of reaction types, including immunological, pharmacological, gastro-intestinal, metabolic, psychosomatic, and toxic reactions.

Immunological

Immunological responses that are considered food allergy related are mediated by IgE immunoglobulins, whereas food intolerances are mediated by non-IgE immunoglobins, and the immune system recognizes a particular food as a foreign body.

Pharmacological

Pharmacological reactions are generally due to low-molecular-weight chemicals which occur either as natural compounds, such as salicylates and amines, or to food additives, such as preservatives, coloring, emulsifiers and taste enhancers. These chemicals are capable of causing drug-like (biochemical) side effects in susceptible individuals.

Gastro-Intestinal

Gastro-intestinal reactions can be due to malabsorption of nutrients or other GI Tract abnormalities.

Metabolic

Metabolic food reactions are due to inborn or acquired errors of metabolism of nutrients, such as in diabetes mellitus, lactase deficiency, phenylketonuria and favism.

Psychosomatic

Some food may elicit a psychological reaction manifesting clinical symptoms, not really caused by the food but by emotions associated with that food. These symptoms do not occur when the food is given in an unrecognizable form.

Toxic Reactions

Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products. Toxic food reactions are caused by the direct action of a food or substance without immune involvement.

Reaction Time

Food allergy reactions are said to have an acute onset time, meaning they tend to occur rapidly, within anywhere from a few seconds to one hour after contact with an allergen. Food intolerance reactions typically occur much more slowly as the body attempts to digest food, beginning anywhere from 30 minutes to up to 48 hours after a meal.

Physiology

Allergies occur when the body's immune system identifies an otherwise harmless substance, say a protein, as harmful. Some proteins or fragments of proteins are resistant to digestion and those that are not broken down in the digestive process are tagged by the Immunoglobulin E (IgE). These tags alert the immune system into thinking that the protein is an invader. The immune system, thinking the individual is under attack, sends white blood cells to attack, and that triggers an allergic reaction.

Food intolerance occurs as the body reacts against a food additive or other substance as the body attempts to digest it, but there are multiple physiological mechanisms that allow this. Intolerance can result from the absence of specific chemicals or enzymes needed to digest a food substance, e.g. hereditary fructose intolerance. It may be a result of an abnormality in the body's ability to absorb nutrients, as occurs in fructose malabsorption. Food intolerance reactions can occur to naturally occurring chemicals in foods, like in salicylate sensitivity. Drugs like aspirin, which are sourced from plants, can also cause these kinds of reactions. Finally, it may be the result of non-IgE-mediated immune responses.

Prevention

For infants, prevention of allergies can begin with breastfeeding for at least 4 months (as opposed to using cow milk, which according to studies prevents or delays the occurrence of atopic dermatitis, cow milk allergy, and wheezing in early childhood). In the case of allergy and celiac disease, a dietary regimen is effective in the prevention of allergic diseases in high-risk infants, particularly in early infancy regarding food allergy and eczema. The most effective dietary regimen is exclusive breastfeeding for at least 4–6 months, or in absence of breast milk, formulas with documented reduced allergenicity, combined with avoidance of solid food and cow's milk for the first 4 months.

For both adults and children, avoiding an allergic reaction can be done by following a strict diet. It is difficult to determine the amount of allergenic food required to elicit a reaction, so complete abstinance from suspected substances is recommended, unless otherwise suggested by a qualified medical professional. It can be difficult to maintain a proper intake of nutrients when avoiding some allergenic foods, since some allergens are also common sources of vitamins and minerals as well as macro-nutrients such as fat and protein. Healthcare providers will often suggest alternate food sources of essential vitamins and minerals which are less allergenic.

For food intolerance in general, the only route to prevention is restricting the diet to exclude common substances that cause intolerance. Typically, more emphasis is placed on management of intolerance.

Management and Treatment

Epinephrine autoinjector, commonly known as EpiPen for life-threatening allergies
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Epinephrine autoinjector, commonly known as EpiPen for life-threatening allergies

The mainstay of treatment for food allergy is total avoidance of the foods that have been identified as allergens. An allergen can enter the body through consumption of food containing the allergen, and can also be ingested by touching any surfaces that may have come into contact with the allergen, then touching the eyes or nose. For people who are extremely sensitive, avoidance includes avoiding touching or inhaling the problematic food. In case the food is accidentally ingested and an anaphylactic reaction occurs, epinephrine should be used quickly, a substance that can relieve airway swelling and improve blood circulation. Other treatments include antihistamines like Benedryl, which blocks the actions of histamines such as itchiness and dilated blood vessels, and steroids, which calm down immune system cells but do not quickly work in cases of anaphylactic reactions. In any case where an anaphylactic reaction occurs, a person should go to the emergency room at a local hospital if possible.

It is highly recommended that people with severe nut allergies carry an epipen and call 911 if symptoms do not go away. Pediatric allergist Scott Sicherer talks about managing allergies in children:


For food intolerance, individuals can try minor changes in diet to exclude foods causing obvious reactions. For many, this may be adequate without the need for professional assistance. However, some food sensitivities may not be noticed for hours or even days after one has digested food, and, therefore, may not be noticeable without help. Persons unable to isolate foods and those more sensitive or with disabling symptoms should seek expert medical and dietitian help. The dietetic department of a teaching hospital is a good start. Food elimination diets are also an option, as these have been designed to exclude food chemicals likely to cause reactions and foods commonly causing true allergies and those foods where enzyme deficiency cause symptoms. These elimination diets are not everyday diets but intended to isolate problem foods and chemicals. Foods with additives are also best avoided.

Prevalence

Six to eight percent of children under the age of three have food allergies and nearly four percent of adults have food allergies. In the United States, food allergy affects as many as 5% of infants less than three years of age and 3% to 4% of adults. There is a similar prevalence in Canada.

Estimates of the prevalence of food intolerance vary widely from 2% to over 20% of the population. So far only three prevalence studies in Dutch and English adults have been based on double-blind, placebo-controlled food challenges. The reported instances of food allergy/intolerance prevalence (by questionnaires) were 12% to 19%, whereas the confirmed instances varied from 0.8% to 2.4%. For intolerance to food additives, the prevalence varied between 0.01 to 0.23%.

References

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