What conditions mimic food allergy?

There are many conditions that can mimic food allergy. It is critical to distinguish true food allergy from other abnormal responses to food, that is, from food intolerance, which can occur in a variety of other illnesses or food poisoning, which occurs when contaminated food is ingested. If a patient says to the doctor, "I think I have a food allergy," the doctor has to consider a number of diagnoses. The possibilities include not only food allergy but also any other diseases that have symptoms brought on by food. These include reactions to certain chemicals in food for example, histamine or food additives, food poisoning, several other gastrointestinal diseases, and psychological symptoms.

Histamine toxicity: Some natural substances (for example, histamine) in foods can cause reactions resembling allergy. Histamine can reach high levels in cheese, some wines, and certain fish, particularly tuna and mackerel. In fish, the histamine is believed to stem from bacterial contamination, especially in fish that has not been refrigerated properly. Remember that mast cells release histamine in an allergic reaction. If a person eats a food that contains a high level of histamine, therefore, he may develop histamine toxicity, a response that strongly resembles an allergic reaction to food. Histamine toxicity has been referred to as pseudoallergic fish poisoning and accounts for over one-third of seafood-related food-borne illnesses, according to the U.S. Centers for Disease Control and Prevention (CDC).

Food additives: Another type of food intolerance is an adverse reaction to certain compounds that are added to food to enhance taste, provide color, or protect against the growth of microorganisms. Consumption of large amounts of these additives can produce symptoms that mimic the entire range of allergic symptoms. (Although some doctors attribute hyperactivity in children to food additives, the evidence is not compelling, and the cause of this behavioral disorder remains uncertain.)

The compounds most frequently tied to adverse reactions that can be confused with food allergy are yellow dye number 5, monosodium glutamate (MSG), and sulfites. Yellow dye number 5 can cause hives, although rarely. MSG enhances flavor, but when consumed in large amounts, can cause flushing, sensations of warmth, lightheadedness, headache, facial pressure, pain in the chest, and feelings of detachment. These symptoms occur soon after eating large amounts of food containing added MSG and are temporary.

Sulfites occur naturally in some foods and are added to others to enhance crispness or prevent the growth of mold. In high concentrations, sulfites can pose problems for people with severe asthma. The sulfites emit a gas called sulfur dioxide, which the asthmatic inhales while eating the food containing sulfites. This gas irritates the lungs and can induce in an asthmatic a severe constriction of the air passages to the lungs (bronchospasm), making breathing very difficult. Such reactions led the U.S. Food and Drug Administration (FDA) to ban the use of sulfites as spray-on preservatives for fresh fruits and vegetables. Sulfites, however, are still added to some foods, and they also form during the fermentation of wine.

Food poisoning: Eating food that is contaminated with microorganisms, such as bacteria, and their products, such as toxins, is the usual cause of food poisoning. Thus, the ingestion of contaminated eggs, salad, milk, or meat can produce symptoms that mimic food allergy. Common microbes that can cause food poisoning include the noroviruses,Campylobacter jejuni, Salmonella, Listeria monocytogenes, Vibrio vulnificus, and E. coli0157:H7.

Lactase deficiency (lactose intolerance): Another cause of food intolerance, which often is confused with a food allergy, specifically to milk, is lactase deficiency. This common food intolerance affects at least one out of 10 people. Lactase is an enzyme in the lining of the small intestine. This enzyme digests or breaks down lactose, a complex sugar in milk, to simple sugars, which are then absorbed into the blood. If a person has lactase deficiency, he does not have enough lactase to digest the lactose in most milk products. Instead, other bacteria in the intestine use the undigested lactose, thereby producing gas. Symptoms of lactose intolerance include bloating, abdominal pain, and diarrhea. In a diagnostic test for lactase deficiency, the patient ingests a specific amount of lactose. Then, by analyzing a blood sample for simple sugars, the doctor determines the patent's ability to digest the lactose and absorb the simple sugars. A lower than normal value usually means a lactase deficiency.

Gluten-sensitive enteropathy: Intolerance to gluten occurs in a disease called gluten-sensitive enteropathy, or celiac sprue. Gluten-sensitive enteropathy is caused by a unique abnormal immune response to certain components of gluten, which is a constituent of the cereal grains wheat, rye, and barley. Although sometimes referred to as an allergy to gluten, this immune response involves a branch of the immune system that is different from the one involved in a classical food allergy. The patients have an abnormality in the lining of the small intestine and experience diarrhea and malabsorption, especially of dietary fat. The treatment for this condition involves the avoidance of dietary gluten.

Other gastrointestinal diseases: Several other gastrointestinal diseases produce abdominal symptoms (especially nausea, vomiting, diarrhea, and pain) that are sometimes caused by food. These diseases, therefore, can resemble food allergies. Examples include peptic ulcer, gallstones, non-ulcer dyspepsia (which is a type of indigestion), Crohn's disease (regional enteritis), cancers of the gastrointestinal tract, and a rare condition called eosinophilic gastroenteritis.

Psychological: Some people have a food intolerance that has a psychological origin. In these people, a careful psychiatric evaluation may identify a traumatic event in that person's life, often during childhood, tied to eating a particular food. The eating of that food years later, even as an adult, is associated with a rush of symptoms that can resemble an allergic reaction to food.