Food Allergies

written by: Jackie Durand RD, CDN
Jackie is a Connecticut-based dietitian and author who creates educational material and helps clients manage their health through small lifestyle changes.

Food Allergy Facts: Getting Diagnosed

Stomach upset, unexplained fatigue and headache? 

You feel that something isn’t quite right, but how do you go about finding what food is bothering you? Working with your healthcare provider and registered dietitian can help you diagnose a food allergy or sensitivity and modify your diet accordingly to feel better fast. Use this guide to educate yourself on potential testing and advocate for the help you need.

What is an allergy?

Your immune system helps protect you from harmful pathogens like bacteria, viruses and disease. An intricate system of specialized white blood cells help detect and destroy potentially harmful invaders before they can affect healthy cells. 

In case of a food allergy, Immunoglobulin E (IgE) antibodies detect a seemingly harmless particle as foreign, and it releases chemicals like leukotrienes and histamines. This response creates a host of negative symptoms in the process of killing the pathogen, especially if you are continuously eating the trigger food.

The top 8 allergens are milk, eggs, fish, shellfish, tree nuts, peanuts, wheat and soy.…but any food can potentially cause an issue.

What are the symptoms?

Most people assume that a food allergy manifests only in the worst way: anaphylactic shock. It’s true that severe reactions can cause the throat to close, and induce seizures or coma. While this most serious result is often dramatized on TV, the average person experiences less bothersome symptoms occurring hours or days after the exposure. This delayed reaction can make pinpointing the cause more difficult. 

Have you experienced any of the following symptoms?

DiarrheaBloatingChronic congestion
HivesTingling lips, mouthShortness of breath
Itching limbsJoint painAsthma

If you have ongoing symptoms like the ones above with no other reasonable explanation, it is time to have a conversation with your doctor. Testing can be done to determine if your symptoms are allergy-related. 

What testing do I need?

Finding out exactly what is bothering you can be a long, drawn-out task unless you have a well-qualified professional to guide you. Most blood tests require approval from a medical doctor, but in some states, your registered dietitian may be able to order these tests. Familiarize yourself with what’s available, and what steps to take to get your results as quickly as possible. 

True allergy testing

IgE antibody blood test: A simple blood test can look for elevated IgE levels. While a positive cannot determine exactly what you’re allergic to, your doctor can refer you to an allergist for more specific testing if necessary.

IgE skin prick test: Your doctor may choose this test instead of blood work. Your skin will be injected with a suspected allergen. If a skin reaction should occur, it shows the presence of a specific allergy. This type of testing works best for environmental allergens, and is not always conclusive for food allergies.

IgG blood test: This antibody is similar to IgE, but less definitive for determining a food allergy. Experts argue that IgG is not an indicator of allergy, so results of an IgG test should always be taken with a grain of salt. 

Celiac sprue panel: If wheat or gluten is a suspected allergen, your doctor will likely also run a celiac disease panel to rule out this disease, which tests for TTG, IgG and IgA antibodies, and would therefore not show up on the traditional IgE test. It is important to continue eating gluten for testing, as absence of the trigger reduces these antibody markers, leading to a false negative result.

What if my allergy tests come back negative?

If allergy testing has given you a definitive answer, congratulations! You can now work with your allergist and registered dietitian to create a plan for avoiding your trigger. 

If not, more tests will be needed. A negative result on an allergy test does not rule out a food sensitivity. It is possible for your immune system to react negatively to a food trigger without sending the typical IgE response. The following tests can identify other immune responses in relation to your trigger.

Food sensitivity testing

Elimination Diet

Sometimes, educated trial and error is the best way to figure out what’s going on. Work closely with a registered dietitian to help systematically eliminate suspected food triggers. If there are multiple suspects, it is best to eliminate one at a time to discover which is truly the cause of your symptoms. 

You will likely be asked to keep a detailed food and symptom log, and you will be given a restricted diet to follow as you monitor symptoms. Expect to eliminate a trigger food for a minimum of four weeks. Keep in mind that symptoms can appear almost immediately, or up to 48 hour later. Keeping a detailed log can help make sense of symptom trends. 

Once your symptoms improve or disappear, the suspected trigger food may be added back in. If symptoms suddenly reappear, your trigger has been identified and long-term diet modifications can be made to avoid it. 

Some additional testing may take away some of the guesswork and speed this trial and error process along. Keep in mind that the following tests are not a substitute for eliminations, and can be costly. The results may be helpful to point you in the right direction, but cannot give definitive answers on their own.

Mediator Release Test (MRT)

This blood test measures the reaction of your white blood cells when exposed to a food. A change in the cell’s liquid to solid ratio indicates that they have released chemicals like histamines to eliminate the threat. Results of an MRT test should always be followed by an elimination diet.

Antigen Leukocyte Cellular Antibody Test (ALCAT)

Wow, that’s a mouthful! ALCAT testing is similar to MRT, but is considered less accurate in some circles. This test indicates whether or not white blood cells shrink in response to a food trigger, which suggests it is releasing histamines, but is not a definitive test.

What if food sensitivity tests come back negative?

This is about the time most people give up and simply live with their symptoms. Don’t lose hope yet. You may not have a food allergy or sensitivity, but you could still have a food intolerance. Your body simply may not have the means to digest or absorb certain foods, causing gastrointestinal upset, bloating, constipation and diarrhea. 

Here are a few things you might want to discuss with your doctor and RD

  • Bacterial overgrowth like SIBO or H. Pylori
  • Lack of digestive enzymes
  • Intolerance to fermentable carbs

The road to determining the cause of your symptoms can be long and arduous. Armed with the right knowledge, you can make educated decisions regarding your care and avoid getting misdirected by the results of the tests mentioned here. Working with a knowledgeable healthcare team can reduce your anxiety throughout this process, and will soon get you on a path of wellness.


1.       “What Is the Best Food Sensitivity Test?,” Health Line (website), accessed February 2020,

2.       “Elimination Diet Protocols,” Today’s Dietitian (website), July 2013, accessed February 2020,

3.       Zukiewicz-Sobczak et al, “Causes, symptoms and prevention of food allergy”, Postept Dermatol Alergol, April 12 2013,, accessed February 2020.

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