Food allergies and sensitivities are illnesses that affect certain individuals in the population when eating foods or food ingredients that most consumers can tolerate with no problem. These illnesses are sometimes called individualistic adverse reactions to foods because they affect only certain individuals in the population. Another catch-all term for these individualistic illnesses is food sensitivities.
Food sensitivities are distinguished from other types of foodborne disease by the fact that they affect only certain individuals in the population. Foodborne infections are caused by infectious bacteria, viruses, and parasites. Foodborne intoxications are caused by the ingestion of chemical substances that are toxic at typical doses of exposures. All consumers are susceptible to foodborne infections and intoxications if they ingest foods that are tainted. Admittedly, the degree of susceptibility does vary between individuals. In contrast with food sensitivities, affected individuals experience adverse reactions from eating typical amounts (or even some times far less) of a food or food ingredient that most consumers can ingest with impunity.
Many different illnesses occur that fall under the broad definition of food sensitivities. Many consumers and some physicians and other health professionals refer to all of these illnesses as food allergy but, no matter what term is used, it is important to recognize that many different types of illnesses occur to foods and food ingredients on an individualistic basis. These different illnesses can require different diagnostic strategies. In all cases, the most common form of treatment is implementation of an avoidance diet - simply avoiding the food or food ingredient that elicits the adverse reaction. But the degree of care needed to implement a successful avoidance diet can depend upon the nature of the illness so it is important for physicians to perform a differential diagnosis and for consumers to know which type of illness that they have.
For the food and related industries, the most important message is that some consumers will NOT know which type of food sensitivity that they experience. These consumers are likely to refer to various food sensitivities as food allergy. To provide the best dietary advice to these consumers, it is important to try to determine which type of food sensitivity is occurring. Especially, it is important to recognize when a true food allergy is involved because avoidance can be difficult due to the very low thresholds that some of these consumers have for the offending food.
Food allergies are abnormal immunological responses to a particular food or food component, usually a naturally occurring protein. Two types of abnormal immunological responses can occur - immediate hypersensitivity reactions and delayed hypersensitivity reactions; both are well documented to occur in certain individuals upon ingestion of specific foods. Immediate hypersensitivity reactions are IgE-mediated reactions with symptoms ensuing within minutes of the ingestion of the offending food. Delayed hypersensitivity reactions are cell-mediated reactions with symptoms developing 48 - 72 hours after ingestion of the offending food. The role of cell-mediated reactions in food allergies is far less well established; IgE-mediated food allergies by contrast are quite well understood.
Food intolerances do NOT involve abnormal responses of the immune system. Three distinct forms of food intolerances are recognized: anaphylactoid reactions, metabolic food disorders, and idiosyncratic reactions. With a few very noteworthy exceptions (e.g. lactose intolerance), the food intolerances are not well understood (put link to section on food intolerances).
Although these illnesses do not truly fall into the category of food sensitivities, it is important to mention allergy-like intoxications at this juncture. Allergy-like intoxications are often confused with true food allergies because the symptoms are often quite similar. Histamine poisoning is the primary example of an allergy-like intoxication. All consumers are susceptible to histamine poisoning if they ingest sufficient amounts of histamine in their diet. Histamine poisoning most typically occurs when certain types of foods are ingested especially certain species of fish (tuna, mackerel, mahi-mahi) that have been subjected to improper, elevated temperatures of storage and allowed to spoil (we do not currently plan to have a link to allergy-like intoxications but might wish to consider such a link at some future time).
A classification scheme for the different types of individualistic adverse reactions to foods or food sensitivities that occur in association with food ingestion is provided in Table 1:
Table 1 is also available as a PDF
Taylor, S. L. and S. L. Hefle. 2005. Food allergies and intolerances. In: Modern Nutrition in Health and Disease, 10th ed., ed. M. E. Shils, M. Shike, A. C. Ross, B. Caballero, and R. J. Cousins, Lippincott, Williams and Wilkins, Philadelphia PA, pp. 1512-1530 .