The terms 'food allergy' or 'food intolerance' should not be used interchangeably. Though both conditions occur after the consumption of certain food items and might have some symptoms in common, the reason behind their occurrence is different. While the immune system is involved in an allergic reaction, food intolerance (also called non-allergic food hypersensitivity) is a chemical reaction and not an immune response. Food intolerance implies that the person has difficulty in metabolizing or digesting that particular food.
In case a person is allergic to a particular food item, he/she must avoid it completely. However, individuals affected by food intolerance might be able to tolerate small amounts of the offending food, without developing the symptoms. Shellfish, milk, eggs, soy, tree nuts, peanuts, wheat, fish, etc., are some of the common food allergens. On the other hand, lactose intolerance is the most common type of food intolerance, followed by gluten intolerance. People who are lactose-intolerant don't have sufficient amounts of lactase, which is an enzyme that is needed to digest a milk sugar called lactose.
Food Allergy vs. Food Intolerance
1 in 20 children and 1 in 100 adults are affected by food allergies. The onset of more than 50% of the allergies occurs during the first year of life, with the most common allergen being cow's milk. However, majority of affected children outgrow this allergy. Eight food items that account for 90% of all allergic reactions include peanuts, tree nuts, fish, soy, wheat, shellfish, milk, and eggs.
Though the incidence of adverse reactions to such food items is increasing, food intolerance is more common than a food allergy. One of the major differences between food allergy and food intolerance is that only the former can lead to anaphylaxis, which is a life-threatening situation that demands immediate medical attention. Allergic reactions involving excessive histamine release can cause anaphylactic reactions (difficulty in breathing), which are responsible for thousands of people in the United States ending up in the emergency ward each year. According to the CDC, food allergies result in more than 300,000 ambulatory-care visits a year among children under the age of 18.
Though food intolerance can be quite discomforting, it is generally not of life-threatening in nature. In case of a true food allergy, each time one consumes a food that one is allergic to, the immune response will be the same, even if one consumes a very small amount of the food allergen. Usually, there is a rapid onset of symptoms in case of an allergic reaction to food. However, in case of food intolerance, the symptoms could appear immediately or even develop anywhere between 12 and 24 hours. The amount of food consumed might also be a determining factor in case of food intolerance reactions. In some cases, the affected person can consume a certain amount without developing an adverse reaction. However, consuming more than this level could give rise to a reaction. However, it must be noted that this amount or level will vary from person to person. Due to the delayed onset of symptoms, food intolerance might be difficult to diagnose. The symptoms occur when one has the offending food more often and in amounts that are larger than the threshold level.
Contributing Factors for an Allergic Reaction
An allergic reaction occurs when the body's immune system identifies an otherwise harmless substance as a threat or a foreign invader. The immune cells that are involved in immune responses aimed at identifying and tackling toxins, pathogens, and other harmful substances include the macrophages, B cells, and the T cells. Majority of the immune system activity takes place in the intestinal tract, the skin, and the respiratory tract. When one eats a food containing a particular protein that the immune system recognizes as a threat, the immune system responds by creating specific disease-fighting antibodies (called immunoglobulin E or IgE). The next time one eats that particular food, it triggers the release of IgE antibodies. The mast cells release histamine, which affects the respiratory system, gastrointestinal tract, skin, or cardiovascular system, thereby causing symptoms such as hives, itching, difficulty breathing, wheezing, etc. Mostly, such a reaction could occur within minutes (immediate onset) or a little later (delayed onset). The symptoms can range from mild to severe.
Contributing Factors for Food Intolerance
On the other hand, food intolerance is not an immune response at all. It is an adverse reaction to a particular food due to the body's inability to metabolize it. More often than not, it occurs when the body lacks certain enzymes that are needed for digesting certain proteins found in food. The most common form of intolerance is that of lactose. Those who are lactose-intolerant experience an adverse reaction on consuming any food that contains lactose, as their body doesn't make sufficient amount of lactase that is required for digesting lactose. The offending food or the trigger could either be a substance that is naturally found in the food or something that is added during processing.
At times, the reaction might be due to the presence of additives. Food additives are chemicals that are added to food to impart color or flavor, or inhibit the growth of bacteria (preservatives). Monosodium glutamate (MSG) and sulfites are known to cause such reactions in some individuals.
Symptoms of a Food Allergy
The symptoms might include:➠
Itching, burning, and swelling around the mouth➠
Skin rash (eczema)➠
Diarrhea, abdominal cramps➠
Breathing difficulties, including wheezing and asthma➠
The symptoms can also be characterized on the basis of the affected parts of the body. For instance, itching and watering of the eyes, stuffy nose and sneezing, itchy and swollen mouth, swollen throat, hives or atopic dermatitis in case of skin, abdominal pain or diarrhea in case of the stomach, wheezing and breathing problems in case of respiratory system, and loss of consciousness, irritability, headache, and convulsions in case the central nervous system is affected.
The most dangerous symptom is the anaphylactic shock, which is a severe allergic reaction that causes hives, swelling of the mouth, tongue, and throat, thereby affecting one's ability to breathe. The symptoms include labored breathing, difficulty in talking, wheezing, loss of consciousness, etc. It is treated by administering an injection of adrenaline.
Symptoms of Food Intolerance
Symptoms of food intolerance can be multiple and non-specific. The symptoms could sometimes be similar to those caused by digestive disorders such as inflammatory bowel disease, gastrointestinal obstructions, or irritable bowel syndrome (IBS), which is why it can be difficult to diagnose. Some of the common symptoms include:➠
Burning sensations on the skin➠
Tightness across the face and chest➠
Diagnosis and Precautionary Measures
Some experts believe that the increase in the incidence of allergies might be due to the lack of exposure to pathogens in the childhood and suppression of the immune system due to the use of drugs, providing formula milk to infants instead of breast milk, etc. Though the effects of desensitization or controlled exposure to allergens are being studied, more research is required in this field. Till then, avoidance is the best option in case of allergies. In case of a rare condition called exercise-induced food allergy, the reaction occurs after someone eats a specific food before exercising. Often consumption of cheese, celery, shellfish, tomatoes, etc., causes such a reaction. Individuals affected by this condition should refrain from eating for a couple of hours before exercising.
While one has to completely avoid food that is one is allergic to, an elimination diet can be followed for several weeks in some cases of food intolerance. Thereafter, one can reintroduce the food slowly. However, one should watch out for any symptoms that are experienced, as one reintroduces the food. If a person has an allergy or intolerance, it is advisable to always read food labels carefully. Once you are aware of the offending food, look at the food labels to ensure that it is not in the list of ingredients in other foods. Be very careful when you are eating at a restaurant/food joint. Do maintain a diary of all food-related reactions so as to identify the food that is causing the reaction.
On a concluding note, the major difference between food allergy and food intolerance involves the onset of symptoms. The symptoms often appear within minutes in case of an allergy, whereas the symptoms might appear slowly, after several hours, in case of a food intolerance. The symptoms last longer and are usually gastrointestinal in nature in case of food intolerance. An allergy can cause an anaphylactic shock, which is life-threatening. Though food intolerance reaction can make you feel very unwell, it is not life-threatening. Even a small amount of allergenic food can cause a reaction, while intolerance reaction occurs when a reasonable amount of food (above one's threshold value) is consumed. While allergies can be diagnosed with tests such as oral food challenges, skin prick tests using food extracts, or tests to check for IgE antibodies/blood (RAST) tests, food intolerance is difficult to diagnose. Food exclusion and reintroduction is often suggested for diagnosing and managing food intolerance. Being a time-consuming procedure, this must be carried out under the supervision of a registered dietitian.