My goals for this lecture were to discuss the basic attributes of an allergic response, common allergies, and validated tests for these allergies. In addition, we briefly discussed commonly understood food intolerances, and their validated tests.
Disclaimer: I reviewed many papers, text books, and review articles for this topic and presented currently accepted topics from peer reviewed journals. I understand that this field is always growing and developing and there are many papers and discussions out there; some of those results were not discussed. Do not use this talk to replace consultation with a medical provider. If there are any concerns about a food reaction please discuss them with your physician. If there is a concern about a possible allergic reaction, please seek medical attention. immediately.
The slide above shows a way to categorize a food reaction as simply as possible. In other words, a food reaction can be initiated by the immune system or it isn't. Anything that isn't, is not considered an allergy but rather a food intolerance. To further categorize the food allergy reaction, I have fields partitioned into IgE or antibody E mediated reactions, a partial IgE reaction, or some other type of immune reaction that does not involve IgE.
Many of you are probabley wondering what IgE is at this point. IgE is an antibody produced by the body. An antibody is a protein produce by the body that identifies a antigen or foreign substance in the body (that foeign substance is a food particle in this case). Antibody E or IgE is a class of antibody that is particularly involved in the allergic response I am discussing above.This reponse is specific since it produces swelling, hives, flushing, and so many other symptoms that we think about when we think about allergies. This is because the response is linked to a response in the body that produces a substance called histamine. The important thing to remember is that IgE is mostly behind this allergy thing! There are other responses as listed above such as mixed or nonIgE immune responses but I will not go into those reponses in depth.
Food intolerances are the non immune mediated response can be further separated into categories. One category is a known toxic reponse such food poisioning from bacterial contamination of food. Another category is an explained pathway such as: lactose intolerance; fructose/short chain carbohydrate intolerance; and food additives or pharmacologic reactions (ie part of the food may contain large amounts of histamine and can create a histamine like reaction). The last cateogry is food intolerance that is not well explained such as irritable bowel syndrome or functional bowel disorders. There is ongoing research into these disorders that appear multifactorial in nature but I will not go further into this subject.
Allergy Symptoms, Allergies, and Validated Tests
Allergy symptoms are symptoms that occur from the IgE mediated histamine response and can be very serious even life threatening. This includes: itching and swelling of the lips, nose, mouth, and tongue; difficulty breath and swelling in the neck; hives, flushing, and swollen skin; nausea, vomiting, diarrhea, and abdomen pain; and even passing out from a drop in blood pressure as blood vessels enlarge. All of these symptoms can lead to a life threatening condition called an anaphylatic reaction and requires immediate medical attention. There are lesser degrees of these reactions as well and they are also due to the same IgE mediated histamine response. Oral food allergy syndrome is an example of this where there is a cross reactivity from one allergen to another and can produce a response to the mouth area as noted below and can also be life threatening. Below is a slide on examples of food allergies and oral food allergy syndrome. Please note that children may have a different likeliness to develop certain allergies, develop more allergies, but also are more likely to outgrow these allergies.
Below is a list of the common validated tests for food allergies on the left side of the slide with a list of unvalidated testing on the right side. There are basically only three validated tests including: skin prick test, serum testing, and oral food challenge. However, even with those three tests most of the tests have to be interpreted by a clinician that knows the patient and can take the whole clinical scenario into consideration. This means a positive test may not indicate an allergy in one patient but a negative test in a different patient may not indicate there isn't an allergy. I know, confusing stuff. For example, if a patient has already had a concerning reaction to a food ie difficulty breathing and facial swelling, then a test with low reactivity may be positive in comparison to another patient with the same result and no history of such reaction being interpreted That is why testing should be navigated with a clinician that knows the patient and the test.
I did not go into detail on the other categories of allergy briefly touched on above: a response when someone has a response that partially involves IgE or doesn't involve IgE. These responses are still lumped into the category of allergy and include such disorders as milk protein allergy in newborns, food protein induced enteropathy, eosinophilic esophagitis, celiac's disease, irritable bowel disease, and many more.
Food Intolerances....what we know....
As noted earlier, we normally group true food intolerances into conditions we can adequately explain and those we can't. Common symptoms of food intolerance include diarrhea, constipation, bloating, and increased flatulence or farting. I did not discuss extra intestinal symptoms such as fatigue, malaise, migraines, mood changes, etc in my talk.
In the pharmacologic category noted above, there are reactions to food that are known to be explained and occur in many people. The condition is not specific to the individual such as caffeine. Caffeine has commonly been used as a laxative in the hospital setting so to say that it induces diarrhea would only confirm that is a reaction that many people have experienced before.
Lactose intolerance and fructose/ short chain carobyhydrate intolerance are the most commonly discussed food intolerances and can be tested with hydrogen breath testing. Lactose is a sugar found in milk and is an enzyme called lactase aids in it's digestion. Lactose intolerance is due to lactase deficiency and can occur early or later in life. Sometimes small a mounts of lactose can still be ingested in the forms of yogurt ie 15 mg but higher ingestions can lead to the symptoms discussed above. Fructose is another sugar found in many foods such as fruit or even high fructose corn syrup. Fructose intolerance is due to problems with transportation of fructose across the gut membrane and is proportional to glucose, another sugar, that is ingested in the same meal. This means that an ingestion of food containing mostly fructose and not a large amount of glucose can cause symptoms; however, if the fructose ingested is similar in proportion to glucose, the patient might not have any symptoms. In addition, digestion of short chain carbohydrates in addition to fructose and lactose such as fructans, galactans, and polyols can also cause symptoms but please refer to my FODMAP post for this information.
IBS or irritable bowel syndrome is a functional bowel disorder that is currently being researched but has been known about in the clinical world for many years. The etiology is thought to be multifactorial in nature. This topic would warrent a nutrition seminar in of itself. In addition, gluten sensitivity is also another multifactorial condition currently being studied and doesn't fit the exact etiology of celiac's disease. These conditions are can be treated with the FODMAP diet as discussed in a previous post on mine here. There are no direct tests for these conditions as the slide for food allergy testing lists some common unvalidated tests often used for these conditions as well. I would also add additional unvalidated tests include:fecal microbiotic analysis, salivary IgA, and intestinal permability.
1. Mahan L, Escott-Stump S, and Raymond J. Krause's Food and the Nutrition Care Process. 13th ed. Elsvier. 2012.
2. Turnbull J, Adams H, and Gorard D. Review article: the diagnosis and management of food allergy and food intolerances. Aliment Parhmacol Ther 2015; 41:3-25.
3. Lorner M, Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance. Aliment Pharmacol Ther 2015; 41: 262-275.