As mentioned previously, there are a variety of adverse reactions with food that can be confused with true food allergies. One such reaction is histamine poisoning. Histamine poisoning is the result of consuming foods containing high levels of histamine, a mediator of allergic reactions in the body. Histamine poisoning is also known as scombroid fish poisoning, because it is often associated with the consumption of spoiled fish, both scombroid, such as tuna and mackeral, and non-scombroid, such as mahi-mahi and sardines (3). Histamine poisoning has also been associated with cheese, particularly swiss cheese. In all of these food products histamine is formed from the growth of bacteria, which converts the naturally occurring amino acid, histidine, into histamine (3). When large doses of histamine are consumed, the body’s ability to metabolize the histamine is overwhelmed. The excess histamine is absorbed, enters the bloodstream, and symptoms very similar to food allergies are observed.
Food intolerances are abnormal responses to food, but unlike true food allergies, they do not involve the immune system of the body. There are several classes of food intolerance, which include metabolic reactions, anaphylactoid reactions, and idiosyncratic reactions (6).
Metabolic reactions are adverse reactions that result from a defect in the body’s ability to metabolize a food component (3), (6). An example of this is lactose intolerance. Lactose intolerance results from a deficiency of the enzyme lactase. As a result, lactose cannot be metabolized, and the undigested lactose cannot be absorbed by the small intestine. Thus the lactose passes into the colon, where bacteria metabolize it into carbon dioxide and water. Symptoms of lactose intolerance include abdominal cramping, bloating, and flatulence.
Anaphylactoid reactions result from the ingestion of substances that bring about the release of histamine from cells within the body (3, 6). This reaction does not involve the IgE-mediated response, and evidence for the existence of the anaphylactoid mechanism is circumstantial (3, 6). An example of this type of reaction is the strawberry reaction because it contains very little protein, no allergies have been identified, and there is no evidence of a strawberry-specific IgE (3). Nevertheless, strawberries have been known to cause allergy-like symptoms. Therefore, an anaphylactoid reaction is a logical explanation.
Idiosyncratic reactions involve adverse reactions that occur in individuals via an unknown mechanism. The best example of this type of reaction is the sulfite-induced asthma reaction (3, 6). Although the mechanism of this reaction is unknown, the relationship of the food to the reaction has been well documented. Asthma is the most common symptom involved, following ingestion of sulfite. Sulfite-sensitive individuals should avoid sulfited foods, but some individuals can tolerate the ingestion of small amounts of sulfites.