Food Intolerance Testing - Miraculous or Misleading?

There is often some confusion about the difference between food allergy and food intolerance so lets look at the difference first of all.

What is a food allergy?

In a food allergy the immune system overreacts to a usually harmless food. When exposed to the food the body misidentifies it and mistakes it as foreign and harmful. In response to the exposure the immune system most commonly produces IgE antibodies (think IgE for Emergency to help you remember!) which cause an immediate reaction to defend itself - chemicals are released by immune cells that cause all the symptoms associated with an allergic reaction like digestive symptoms, swelling, hives, itching skin, difficulty breathing, wheezing, dizziness and in some cases anaphylaxis.  

Food allergies can be fatal, unlike a food intolerance or sensitivity. In extreme cases, ingesting or even touching a small amount of the allergen can cause a severe reaction. Eight foods as responsible for the majority of allergic reactions: cows milk, eggs, fish, peanuts, shellfish, soy, tree nuts, wheat (1). 

What is a food intolerance?

Food intolerances, sometimes called food sensitivities, are different because eating the food doesn’t cause IgE antibodies or chemicals to be released but you may still experience some similar unwanted symptoms.  

A food intolerance response usually takes place in our digestive system. Symptoms are commonly gut related but can extend to headaches, brain fog and joint pain. Unlike food allergy reactions, symptoms of intolerance can occur hours after eating the food so it can sometimes be hard to pinpoint the culprit.

A food tolerance usually occurs if we are unable to properly break down a component of a food. This might be because we lack the enzyme we need to break down the food (e.g. lactase in lactose intolerance, the natural sugar found in milk and many milk products), or it might be a sensitivity to a food additive or to a specific part of the food (2).

 

Can we test for food allergies and food intolerances?

Food allergy testing and lactose intolerance testing can be done through the NHS (in the UK) or your medical practitioner. The main clinically validated tests are:

  • IgE testing – blood or skin prick/patch tests (for food allergies)

  • Hydrogen breath test or blood test (for lactose intolerance)

Although not a food allergy or intolerance, blood tests for coeliac disease are also available on the NHS. Coeliac disease is an autoimmune disease where the immune system attacks the body’s own tissues when gluten is eaten (the proteins found in wheat, rye, barley and triticale).

There is currently no scientifically proven way to test for other food intolerances, despite the many commercially marketed food intolerance tests you might see on the internet including:

  • IgG Food Intolerance Tests e.g. York Test

  • Stool tests

  • Hair analysis tests

  • Kinesiology

The commercial IgG food intolerance tests are the ones I see and hear about most often so I wanted to go into this in a bit more detail so you can understand why I do not recommend them!

 

Why IgG food intolerance tests lack scientific validity

Food intolerance tests look for IgG antibodies in our blood. These companies suggest that the higher the IgG antibodies, the more intolerant you are to that food.

However, when we look at the evidence the opposite seems true!

Many studies have shown that the presence of IgG antibodies to specific foods is the natural, physiologic response to foods we eat, so they simply indicate that a person has previously been exposed to that food (3, 4, 5). Hence so many people who take them come back with a huge long list of foods, often the ones they eat most often, and this leads to completely unnecessary dietary restriction and increased risk of nutrient deficiency.

Other studies have also shown that children with allergies (IgE), seem more likely to be tolerant to foods they have high IgG antibodies to in later life, when building tolerance with immunotherapy increasing IgG antibodies shows improved tolerance to a food, and that increasing IgG antibodies may actually have a protective effect by inhibiting IgE mediated allergic reactions (6, 7, 8, 9).

 

Food intolerance testing in IBD

There have been some studies looking at IgG food intolerance testing in IBD (10, 11, 12). Although some small trials have shown some positive effects in symptoms through IgG directed food exclusion diets, these studies have their limitations and the underlying mechanisms of IgG antibodies in IBD is unclear. It has also been suggested that increases in IgG antibodies may be a result of inflammation, disease activity and damage to the intestinal lining, rather than a cause (13).

 

Food intolerance in IBD – is it the food or the disease?

Lactose intolerance is common in Crohn’s Disease and you can read more about this here. Lactose intolerance for some people may be secondary lactose intolerance as a result of Crohn's Disease. Some fine its more present when disease is active but absent when disease is in remission.

We are often quick to blame food but it is important to distinguish whether it is actually the food causing the problem or if it is, in fact, the underlying disease, as suggested in the paper above.

I often see that peoples tolerance to food hugely decreases when in a flare but increases again when in remission. If there is inflammation in the gastrointestinal tract then food passing through that, no matter what it is, may cause pain and discomfort. This is why its often recommended that people follow a simple low fibre/low residue diet during a flare to reduce irritation as the food passes through the intestines.

There is not very much data on the prevalence of other food intolerances in IBD but in one small study of 41 patients with CD and UC, 65% of them self reported being intolerant to one or more foods (14). In my clinical practice working every day with people with IBD, I do see food intolerance a lot – there does seem to be some common culprits but everyone with IBD is different.

 

What should I do if I think I have a food intolerance?

  1. Do not waste your money buying a commercial food intolerance test. The gold standard and only way to identifying a food intolerance is to remove a food for a period of time then reintroduce it back in and monitor symptoms. However, this should only ever be done under the guidance of a dietician or nutritionist to help you identify which food is appropriate to exclude, if any, and to prevent nutrient deficiency.

  2. Keep a food, lifestyle, and symptom diary - this can help to identify which foods might be causing you issues but tracking lifestyle habits alongside symptoms can also help us identify whether it might actually be unrelated to food and its something like stress that is impacting symptoms.

  3. Save your money and seek advice from someone who is qualified to help you so you can do it safely and avoid overly restricting your diet.

I cannot emphasise enough how important it is in a condition like IBD, where risk of nutrient deficiency is already high and food related quality of life is low, that we do not restrict foods or food groups without proper supervision from a nutritionist or dietician.

References

  1. British Society for Immunology (2017) Allergy Policy Briefing. Available from: https://www.immunology.org/policy-and-public-affairs/briefings-and-position-statements/allergy. (Date accessed: 25 March 2021)

  2. American Academy of Allergy, Asthma & Immunology (2021) Food Intolerance versus Food Allergy. Available from: https://www.aaaai.org/conditions-and-treatments/library/allergy-library/food-intolerance. (Date accessed: 25 March 2021)

  3. Antico A, Pagani M, Vescovi P, P, Bonadonna P, Senna G (2011) Food-Specific IgG4 Lack Diagnostic Value in Adult Patients with Chronic Urticaria and Other Suspected Allergy Skin Symptoms. Int Arch Allergy Immunol;155:52-56. doi: 10.1159/000318736

  4. Hunter J. O. (2005). Food elimination in IBS: the case for IgG testing remains doubtful. Gut, 54(8), 1203.

  5. Siroux V, Lupinek C, Resch Y, Curin M, Just J, Keil T, Kiss R, Lødrup Carlsen K, Melén E, Nadif R, Pin I, Skrindo I, Vrtala S, Wickman M, Anto JM, Valenta R, Bousquet J. (2017) Specific IgE and IgG measured by the MeDALL allergen-chip depend on allergen and route of exposure: The EGEA study. J Allergy Clin Immunol ;139(2):643-654.e6. doi: 10.1016/j.jaci.2016.05.023. Epub 2016 Jun 22. PMID: 27464960.

  6. Tomicić S, Norrman G, Fälth-Magnusson K, Jenmalm MC, Devenney I, Böttcher MF. High levels of IgG4 antibodies to foods during infancy are associated with tolerance to corresponding foods later in life. Pediatr Allergy Immunol. 2009 Feb;20(1):35-41. doi: 10.1111/j.1399-3038.2008.00738.x. Epub 2008 Mar 12. PMID: 18346097.

  7. Savilahti EM, Rantanen V, Lin JS, Karinen S, Saarinen KM, Goldis M, Mäkelä MJ, Hautaniemi S, Savilahti E, Sampson HA. Early recovery from cow's milk allergy is associated with decreasing IgE and increasing IgG4 binding to cow's milk epitopes. J Allergy Clin Immunol. 2010 Jun;125(6):1315-1321.e9. doi: 10.1016/j.jaci.2010.03.025. Epub 2010 May 11. PMID: 20462631; PMCID: PMC3289532.

  8. Sugimoto M, Kamemura N, Nagao M, Irahara M, Kagami S, Fujisawa T, Kido H. Differential response in allergen-specific IgE, IgGs, and IgA levels for predicting outcome of oral immunotherapy. Pediatr Allergy Immunol. 2016 May;27(3):276-82. doi: 10.1111/pai.12535. Epub 2016 Feb 5. PMID: 26764899.

  9. Burton OT, Logsdon SL, Zhou JS, Medina-Tamayo J, Abdel-Gadir A, Noval Rivas M, Koleoglou KJ, Chatila TA, Schneider LC, Rachid R, Umetsu DT, Oettgen HC. Oral immunotherapy induces IgG antibodies that act through FcγRIIb to suppress IgE-mediated hypersensitivity. J Allergy Clin Immunol. 2014 Dec;134(6):1310-1317.e6. doi: 10.1016/j.jaci.2014.05.042. Epub 2014 Jul 16. PMID: 25042981; PMCID: PMC4261076.

  10. Gunasekeera, V., Mendall, M.A., Chan, D. et al. Treatment of Crohn’s Disease with an IgG4-Guided Exclusion Diet: A Randomized Controlled Trial. Dig Dis Sci 61, 1148–1157 (2016). https://doi.org/10.1007/s10620-015-3987-z

  11. Xiao N, Liu F, Zhou G, Sun M, Ai F, Liu Z. Food-specific IgGs Are Highly Increased in the Sera of Patients with Inflammatory Bowel Disease and Are Clinically Relevant to the Pathogenesis. Intern Med. 2018 Oct 1;57(19):2787-2798. doi: 10.2169/internalmedicine.9377-17. Epub 2018 May 18. PMID: 29780153; PMCID: PMC6207831.

  12. Wang, H. Y., Li, Y., Li, J. J., Jiao, C. H., Zhao, X. J., Li, X. T., Lu, M. J., Mao, X. Q., & Zhang, H. J. (2019). Serological investigation of IgG and IgE antibodies against food antigens in patients with inflammatory bowel disease. World journal of clinical cases, 7(16), 2189–2203. https://doi.org/10.12998/wjcc.v7.i16.2189

  13. Fedor, I., Zold, E., & Barta, Z. (2019). Food-specific IgG Antibodies in Crohn's Disease: What Came First, the Chicken or the Egg?. Internal medicine (Tokyo, Japan), 58(14), 2123. https://doi.org/10.2169/internalmedicine.2379-18

  14. M. Ballegaard, A. Bjergstrøm, S. Brøndum, E. Hylander, L. Jensen & K. Ladefoged (1997) Self-Reported Food Intolerance in Chronic Inflammatory Bowel Disease, Scandinavian Journal of Gastroenterology, 32:6, 569-571, DOI: 10.3109/00365529709025101

Clemmie Macpherson