Hey! This entry contains some general information and classifications regarding food allergies, sensitivities, and intolerances. There is no standard way of describing each in the literature, so I am sharing this post to inform you of one simple, straightforward classification. It is the way I am learning it in my Food Allergies and Intolerances course in grad school. I also had a video assignment for school which I put at the end of the article. Its not very exciting, lol, but it basically explains this info in a video form.


There are three categories of adverse food reactions: psychological, food poisoning (toxic), and non-toxic. Under the non-toxic category, there are non-immune mediated reactions (food intolerances) and immune mediated reactions (allergies and sensitivities). The table below gives an overview of each type of food reaction.

Adverse Food Rxn Description Symptoms Timing Testing
Psychological Just don’t like a food for any number of reasons Ask what foods you don’t like
Food Poisoning Bug in food that makes you sick when you eat it, also did or would likely make others sick if they ate it Vomiting, diarrhea, stomach cramps, nausea, fever Starts 4-6 hrs after eating;

Resolves within 24-48 hrs

Done if many people get sick
Allergy IgE antibody immune system response; can be a life-threatening reaction (e.g. peanut allergy) Hives, swelling of the face, and difficulty breathing, anaphylaxis Immediate or up to a few hours after coming in contact with food Skin prick test;

IgE antibody blood test for specific food

Sensitivity Non-IgE (or IgG) antibody mediated immune response Many different symptoms possible – wherever the body can express inflammation Few minutes to few days after consuming food Elimination-reintroduction diet;

IgG antibody blood test for specific food

Intolerance Rxn due to not having enzymes to digest a food properly (e.g. lactose intolerance) Symptom is dependent on type of intolerance you have – e.g. facial flushing (alcohol intolerance); being “amped up” for many hours (caffeine intolerance) Typically seen very shortly after consuming the food Elimination-reintroduction diet;

Genetic Testing;

Breath Testing


Psychological Food Reactions

A psychological food reaction is pretty straight forward. This is when you simply don’t like a food for any number of reasons. Perhaps you ate it once many years ago and it made you very sick. Or, you don’t like the texture of the food, or perhaps it tastes bland to you, is too bitter, too pungent, etc…

We test for psychological food reactions by asking what foods you do not like.

Food Poisoning (Toxic)

Food poisoning occurs when you eat something that is contaminated. The food could contain some bacteria or virus that is present because the food was past its expiration date, the person preparing the food did not wash their hands properly, the food was not washed properly… really for any number of reasons. What is important to note is that the bug in the food you ate is not good for you and your body is doing whatever it can to get that bug out. So, you have vomiting, diarrhea, and the associated pain such as stomach cramping. You would also like feel very nauseous and could have a fever.

With food poisoning, all or most other people who also ate that contaminated food would get sick as well. The illness would start after four to six hours post consumption and would resolved within one or two days. If many people contracted the same illness as you, tests could be done to find the source of contamination and the source could be remediated to prevent future illness in other people.


Non-Immune Mediated

Food Intolerances

Food intolerances occur because we lack an enzyme that is needed to digest a certain food. The food intolerance we are typically most familiar with is lactose intolerance. Those who don’t have the lactase enzyme to digest the lactose in dairy may experience bloating, pain in the lower abdomen, gas, loose stools, or vomiting after eating foods containing dairy. There are a variety of other intolerances as well. Individuals with alcohol intolerance experience facial flushing when they drink alcohol. Those intolerant to caffeine get amped up when they drink it and the effect will last for many hours.

There are a few ways to test for food intolerance. The first is an elimination and reintroduction diet. This diet works by eliminating foods to which you may be intolerant. After 8 weeks, you reintroduce the food. If after reintroducing the food you notice symptoms, you can suspect that you are intolerant to it. Some genetic and breath tests are also available to test for food intolerances. Both are relatively new and not used as frequently as the elimination and reintroduction test.



Food Allergies

Food allergies are easily recognized. Think of a severe peanut allergy. Someone who is highly allergic to peanuts accidently eats a peanut. What happens? They can develop hives, swelling of the face, and difficulty breathing due to their throat closing (anaphylaxis). Individuals with food allergies often carry epi-pens for this reason. The epi-pen is injectable adrenaline that will keep their throat from closing up in the event they come into contact with something they are allergic to. They also likely carry diphenhydramine (Benadryl), an antihistamine, which may slow down the progression of their reaction until they can reach a hospital. With food allergies, the reactions can be life threatening and the symptoms show up immediately or within a couple of hours after contact to the allergen.

To test for food allergies, a skin prick test or a IgE antibody blood test for a specific food can be done. IgE refers to the type of antibody, or protein, that is produced by the body when it ingests a food it sees as being toxic.


Food Sensitivities

Food sensitivities are caused by non-IgE antibodies, most notably IgG. Because the antibody is different, the immune response is different, and different symptoms arise. These symptoms can happen anywhere throughout the body, wherever inflammation can occur. Examples of symptoms include fatigue, stomach aches, migraines, eczema, sore throat, and brain fog, although there are many more potential symptoms. And, these symptoms are often delayed. Sometimes they are seen within minutes after consuming a food, although it is not uncommon for symptoms to develop three days after eating a food.

To test for food sensitivities, an elimination-reintroduction diet can be done. The protocol is the same as what was described for food intolerances. An IgG antibody blood test for specific foods can also be performed.



So, there are a number of ways that you can be adversely reacting to foods. Psychological reactions, food poisoning, and severe allergic reactions to food are pretty straightforward. Food intolerances and sensitivities are a bit harder to grasp. Just remember, there is no set definition in the literature, which adds to the confusion, but for the purpose of this article, we say that food sensitivities are immune-mediated IgG adverse food reactions and food intolerances are caused by an enzyme deficiency. The symptoms of food sensitivities can be difficult to track as they may not occur right away and the way symptoms are experienced is individualized. For instance, one person may be sensitive to walnuts and get migraines 30 minutes after eating them, and another person also sensitive to walnuts has joint stiffness occurring two days after consuming walnuts. Its not very straightforward. Food intolerances are more straight forward because individuals tend to experience the symptoms in a similar way and the symptoms typically occur soon after the food is consumed. In both cases, a food elimination and reintroduction after a period of eight weeks is the most reliable and effective way to test for both food sensitives and intolerances. Concurrent and/or follow-up testing may confirm whether the adverse food reaction is a sensitivity or intolerance, although at the end of the day, avoiding the food causing an adverse reaction is essential regardless of the origin of the problem.


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