An adverse food reaction is any abnormal response to an ingested food, regardless of what causes the reaction.  If the immune system is involved the response may be a food allergy or a food sensitivity.  If the immune system is not involved, the response is considered food intolerance or some other cause. Non- immune reactions include jitteriness from caffeine and intolerances such as lactase deficiency. 


Food Allergies

Immune reactions are divided into those that are true allergies and those that are considered food sensitivities. With a true food allergy the immune cells that produce immunoglobulin E (IgE) respond. These can result in the classic presentations of food allergy, such as hives or anaphylaxis after ingestion of the offending food. Testing for food allergies is usually done with a blood test or skin test. If you think you have an allergy you would see an allergist.

Food Sensitivities

Reactions that are the result of immune cells that do not produce IgE are known as non–IgE-mediated food reactions.  Non–IgE-mediated food reactions cannot be identified with classic allergy testing, either blood or skin tests.  The food sensitivity reactions can vary from person to person and often are systemic, and may affect many systems.  Some people experience digestive (GI) distress including diarrhea, pain, or cramping. Other symptoms that may indicate food sensitivity include skin responses, muscle pain (fibromyalgia), joint pain, headaches or fatigue. These symptoms are often chronic.

Food sensitivities can be delayed, occurring from 45 minutes to 72 hours after ingestion. The delayed onset of symptoms makes them difficult to identify. If you think you have food sensitivity, you need to speak with a dietitian who is familiar with food sensitivities. There is a specific blood test that is available to identify food sensitivities. The most accurate will measure the effect on the blood  solids as a result of the release of mediators such as cytokines and prostaglandins.

Food Intolerances

Food intolerances such as lactase deficiency can produce GI symptoms similar to food sensitivities such as diarrhea, pain and cramping, however it does not involve the immune system. When the food is ingested, it is not properly broken down or absorbed. The undigested food provides food to the gut bacteria and the result is usually gas, bloating, and often, diarrhea.  These symptoms are a result of the bacteria digesting the sugars; it is fermentation. These symptoms are often diagnosed as Irritable Bowel Syndrome (IBS). With lactose intolerance the person does not produce enough lactase (the enzyme that digests the lactose or milk sugar). There are other foods that require enough of specific enzymes produced in the small intestine. If the person is not producing enough of certain enzymes, they will be more likely to have food intolerances.  The foods that contain “fermentable sugars” include lactose, fructose, sugar alcohols and other starches. These have been identified and are referred to as FODMAPs-fermentable oligo-, di-, monosaccharides, and polyols.  Lactose intolerance and fructose intolerance can be identified with a breath test, if you think you have a lactose or fructose intolerance, speak with your doctor. There is not a specific test for other intolerances other than eliminating the foods and then challenging them (adding back into the diet).  If you think you have food intolerances, you may need to work with a dietitian who is familiar with the FODMAP approach.