Food allergy and food intolerance, while often lumped together because they elicit side effects after the ingestion of certain foods, occur by different mechanisms physiologically and cause a variety of symptoms.
Food allergy suggests an immune-mediated response to food caused by chemical mediators or actual cells that attack specific proteins on foods. The manifestations can be acute or delayed.
Acute Symptoms of Food Allergy
The acute reactions to true food allergies are, perhaps, widely recognized. These include urticaria (hives), angioedema (swelling of the lips and/or the area around the eyes), lightheadedness or anaphylaxis, where acute airway closure, acute shortness of breath, wheezing and difficulty swallowing may ensue--a true medical emergency. Anaphylaxis can also manifest as acute nausea, abdominal pain, vomiting and/or diarrhea, within minutes after food exposure. It can also lead to loss of consciousness.
Delayed Symptoms of Food Allergy
Delayed or chronic reactions associated with food allergies affect the same organ systems as the acute reactions--namely the skin, respiratory system and the gastrointestinal tract--and usually manifest as a flare-up of pre-existing conditions, such as asthma, recurrent rashes (eczema or dermatitis herpetiformis), or certain gastrointestinal illnesses. With gastrointestinal conditions, symptoms often include one or a combination of bloating, flatulence, nausea, abdominal pain, fatty stools, vomiting, heartburn, early satiety (sensation of fullness after a meal), or weight loss and malnutrition (or, in the case of infants and children, failure to thrive).
Food Intolerance Symptoms
Food intolerance, on the other hand, occurs by any number of mechanisms, but it is not caused by a true immune response. According to Dr. James T. Li, M.D., Mayo Clinic asthma and allergy specialist, causes can include enzyme deficiencies, whereby individuals lack or have inadequately functioning enzymes to break down components of certain foods; heightened responses to food components, such as profound jitteriness or irritability that some experience with caffeine-containing products; or headaches after ingesting additives in certain foods. Food intolerance can also be caused by food poisoning and certain chronic digestive conditions, such as celiac disease, as well as by psychological associations with certain foods. Symptoms of food intolerance primarily affect the gastrointestinal system and include nausea, vomiting, diarrhea, bloating, flatulence and, occasionally, weight loss (secondary to malabsorption).
