by Rachel Stuck, RDN
Unexplained GI distress and brain fog have led many to believe that they have a food intolerance or sensitivity. Understandably, these symptoms leave many people looking for answers, which they may try to find through a food allergy, intolerance, or sensitivity test. Although it would be great to use a special test to determine which foods are causing GI distress and related symptoms, science does not necessarily support the results. If you are considering food allergy testing in a doctor’s office or with an over-the-counter food sensitivity test, it is important to know the differences and understand what you can learn from these tests and what you cannot.
Food allergy testing is completed by a doctor or allergist in a doctor’s office. When someone has a food allergy, their body initiates an immune response when the trigger food is present. The immune response is the release of the antibody immunoglobulin E (IgE), so to determine if someone has a food allergy, a doctor or allergist may complete an IgE blood test. After the blood is drawn, it is sent to a laboratory where different foods can be introduced and tested for the IgE response. If increased IgE is recorded when a food is introduced, the individual has a food allergy.
You can also use a skin test to detect food allergies. A skin test is done by lightly pricking or scratching the skin and then applying a small drop of food liquid on the skin. If the skin becomes irritated from the exposure to food liquid, this can indicate that you are allergic to that food. This is a common test that is accepted as reliable.
Unfortunately, food intolerance tests and food sensitivity tests that can be purchased online or over the counter are not as clear as food allergy tests. Unlike food allergy tests, which detect immunoglobulin E (IgE), sensitivity or intolerance tests typically look for the presence of immunoglobulin G (IgG). IgG antibodies have not been proven to be a reliable marker for identifying food intolerances or sensitivities. This is because most people produce IgG antibodies when they eat any food, and so the results often show the individual’s most commonly eaten foods as foods to avoid.1 For example, if you eat two eggs with whole grain toast every morning, there is a high probability that eggs and wheat will both come back as foods to avoid. There is also a possibility that an individual with a diagnosed allergy will use an IgG test and be led to believe that they no longer have that allergy. This could prompt the individual to include the food and increase their risk of reaction.
Allergists, doctors, and professional organizations that specialize in food allergy treatment do not use or recommend IgG testing due to the lack of evidence to support clear and consistent results.2,3 This is also why insurance companies will not cover the cost of food sensitivity or food intolerance testing.
That being said, food intolerances or sensitivities do exist. Unfortunately, there is not yet a researched-backed test that can identify which foods you should consider avoiding.
Many people struggle with food sensitivities and intolerances, and for some it has been easy to identify foods that cause bloating, GI distress, headache, brain fog, etc. The common trigger foods include dairy and gluten, and even a few raw vegetables like garlic, onions, and green peppers. If this is the case for you, avoid the food as best as you can or aim to include only very small amounts of the food at a time to assess if there is a tolerable amount of the food that you can include without uncomfortable effects.
The next factor to consider is the health of the gut microbiome. The gut microbiome plays an important role in digesting and absorbing food, and when the gut microbiome is damaged it can lead to a more permeable intestinal lining. An intestinal cell lining that is more permeable than it should be will allow undigested food particles to leak through. This can cause a heightened immune response that causes GI distress, pain, inflammation, brain fog, and symptoms similar to a food allergy or intolerance. To support the gut, aim to include a variety of fiber-rich vegetables, high-quality proteins, and healthy fats. Also, you should avoid processed foods and excessive alcohol because both will damage the gut and can lead to a severe bacterial dysbiosis, or imbalance. Consider introducing a probiotic, following a good sleep schedule, and moving your body daily.
Before starting an elimination diet, it is best practice to reach out to a dietitian, physician, or health care professional. Health care professionals will be able to offer you guidance and support on how to follow an elimination diet and still maintain normalcy.
If you are considering an elimination diet, you may first want to try keeping a 7–10 day food diary that lists all the foods you eat as well as the days and times that you feel discomfort or other symptoms. This can also help you identify the foods that you absolutely need to avoid and the ones that you tolerate well.
Be patient with yourself as you get started. It is challenging to follow an elimination diet perfectly and you will have slip-ups. Don’t dwell on mistakes; just do your best to stay on track.
Registered Dietitian Nutritionist Rachel Stuck has a background in culinary arts and nutrition counseling. Rachel takes a positive approach to nutrition: she avoids recommending restrictive diets and instead focuses on helping people choose foods that promote health and well-being. She is passionate about empowering and assisting Ixcela members as they develop their unique, gut-healthy lifestyles.
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