Do you have symptoms that seem to mysteriously come and go, such as brain fog, fatigue, headaches, joint pain, or digestive issues? Or are you generally just not feeling “right”, and suspect it might be related to your diet?

If so, there’s a good chance you could be dealing with an undiagnosed food sensitivity. What’s more, the food you are sensitive to may just be one you would never suspect. In fact, it’s quite possible that a seemingly “harmless” food that you’ve been eating (maybe even daily throughout your whole life!) is to blame for your symptoms!

And yes, food sensitivities can be behind your symptoms even if you are eating a clean, Paleo, or AIP diet!

In this article, I will answer the question “what is a food sensitivity” (hint: it is NOT the same as a food allergy!), how to know if you have one, and what to do about it.

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The Difference Between A Food Sensitivity and Food Allergy

The first thing I want to note is that food allergies and food sensitivities are two very different things. A food allergy triggers an extreme and potentially life-threatening reaction, known as an IgE-mediated immune response. This happens whenever you are exposed to a certain type of food, such as peanuts or strawberries.1

Most allergic reactions happen within minutes and can range from mild—think hives or stomach cramping—to severe, such as anaphylaxis, which can impair your breathing, cause a dramatic drop in blood pressure, and affect your heart rate.2

 Due to the severity of food allergies, you likely already know whether or not you have one.

A food sensitivity, on the other hand, is more difficult to diagnose because it triggers an IgG reaction in your system, which is a delayed immune response. It could take up to 72 hours for symptoms of a food sensitivity to present. The problem with this delayed response is that you probably eat a wide range of foods in the time it takes for symptoms to appear. This makes it difficult for you to spot a pattern between the specific foods you eat and your symptoms.

For example, let’s say you’ve been having migraine headaches and digestive issues. You eat scrambled eggs, fresh sliced tomatoes, and a banana every morning for breakfast. You think maybe it’s something in your breakfast that’s bothering you. So on Monday, you decide not to have the scrambled eggs to see if you get the migraines and digestive issues. Later on in the day, the headache and digestive issues are still there, so on Tuesday, you decide to try eliminating the tomatoes and your symptoms once again return. Well, it could be that the eggs from two days prior are actually causing your migraines and digestive issues, and it’s just taken this long for the sensitivity symptoms to appear.

Additionally, food sensitivities can produce a wide array of symptoms depending on which area of your body the antibodies attack. So you may not even realize that your skin rashes or joint pain are diet-related.

Common signs of a food sensitivity:
  • Fatigue
  • Brain fog and difficulty concentrating
  • Joint pain
  • Headaches or migraines
  • Eczema
  • Rashes and skin irritations
  • Stomach aches
  • Acid reflux
  • Bloating
  • Constipation or diarrhea
  • Unexplained weight gain or loss
  • Behavioral issues (in children)

Fortunately, with a scientific approach, you can take out the guesswork and identify which foods are causing your symptoms.

Identifying Food Sensitivities with an Elimination Diet

The best way to discover your food sensitivities is to complete an elimination diet. This means you take out the most common inflammatory foods from your diet and then add them back in one at a time to see if you have a reaction. It’s like getting to do your own science experiment on your diet!

First, you’ll go through the elimination phase. One component of this phase is to remove the most toxic foods from your diet for good! These foods are damaging to your health, so even after completing the elimination diet, you won’t be adding these back in.

Toxic foods:
  • Sugar
  • Alcohol
  • Caffeine
  • GMOs
  • Artificial sweeteners
  • Additives, preservatives, and dyes
  • High-fructose corn syrup
  • Processed food, junk food, and fast food
  • Trans or hydrogenated fats

The other component of the elimination phase is to remove all inflammatory foods from your diet for two weeks.

Most common inflammatory foods:
  • Gluten*
  • Dairy*
  • Corn
  • Soy
  • Eggs
  • Nightshades (tomatoes, peppers, potatoes, and eggplant)
  • Citrus
  • Yeast
  • Gluten-free Grains
  • Legumes

*Gluten and dairy are the top 2 most inflammatory foods and I do not recommend ever adding them back in, particularly if you have an autoimmune or thyroid condition.

Once you’ve removed all of these foods from your diet, you will begin to slowly reintroduce the inflammatory foods one at a time in order to test your body’s response to individual foods.


Specifically, you will eat a particular food three times a day for three days. The idea here is to temporarily bombard your system with each food to produce a noticeable and definitive response. If that food is causing inflammation for you, I want to give your body the best chance to determine that, rather than letting silent inflammation creep in! You also want to make sure your results are clean and reliable, which is why you’ll test only one food at a time.

Here is the exact reintroduction process:

  • Introduce one food at a time
  • Eat the reintroduction food three times a day for three days
  • Record whether or not you experience any symptoms
  • Go back to the program for three days in between each reintroduction food
  • If you have a reaction, take the food back out and return to the program guidelines until you are symptom-free
  • If you don’t have a reaction, take the food back out until you have finished the reintroduction phase
  • Add all safe foods back in after you’ve completed the reintroduction phase

You can follow this same process with any food you’d like to test, even if it’s not on the list. For example, if you suspect you are sensitive to avocados you can remove them from your diet for 2 weeks and follow the reintroduction protocol to gauge your body’s response.

By paying close attention during this phase, you will be able to pinpoint exactly which foods trigger a reaction and what types of symptoms they produce. It can be a very enlightening and empowering process to finally identify what’s been causing your symptoms and, best of all, put an end to them!

IgG Food Sensitivity Blood Test

I always recommend an elimination diet first because your body knows better than any test. However, even a comprehensive elimination diet only tests the most common inflammatory foods. If you are looking to go a step further, food sensitivity testing is a great way to get a more comprehensive analysis of different foods so you can be as informed as possible.

I’ve personally found the best results with a company called Cyrex, which uses a blood test to measure your immune response to 180 foods in both their raw and cooked form. Each food is then given a green, yellow, or red light ranking, so you know which foods are safe, which to watch out for or minimize, and which to avoid completely.

The advantage of doing the blood test in conjunction with following an elimination diet is that it lets you collect as much information as possible about what is going on inside your body. The downside of this type of testing is that it is not always 100% accurate. If your gut is leaky, you may show a reaction to food particles that are escaping into your bloodstream that would not normally trigger an immune response if your gut was healthy. Also, if you’ve already removed a food from your diet for health reasons, you could get a false negative since your body is not currently producing antibodies for that food for the test to detect.

At the end of the day, how you feel is the best indicator. Knowing and really listening to your body is going to be what gets you the best results.