Digestive Disorders

The Problem With IgG Food Sensitivity Testing (and what to do instead)

I can’t tell you the number of folks who come to my office with a list of foods they cannot eat.  They have removed them from their diet in the hopes of reducing or healing their GI issues, but when the gas, bloating, and annoying bowel habits don’t change, they do not add the foods back into their diets.

Why is this?

Many people have had IgG Food Sensitivity Testing by an alternative medicine provider – or purchased the test from a lab – and are told to avoid these foods to feel better.  And I totally understand!  I have Irritable Bowel Syndrome (IBS) and would try nearly anything to heal my gut.

BUT, there is a problem with the IgG Food Sensitivity Tests:  Their validity and claim of sensitivity are not backed by science.

As a Registered Dietitian (RD), I was trained in evidence-based nutrition and through this training, learned how to critically review research data and share it with my clients and the community.  I tend to not believe the “hype” when I see an article touting a cure for a disease or one that vilifies or extols a specific food as the key to declining or optimal health until I have read the original research report and pored over the references.

Because so many folks have asked me about the IgG Food Sensitivity Tests, I thought I would share the research with you, but first I want to explain the difference between correlation and causation.

correlation means there is a connection between two or more things.

For example, male-patterned baldness is correlated with heart disease. Does that mean that male-patterned baldness causes heart disease? No! Correlation just implies that there is simply a connection; both things happen to be occurring at the same time but one is not due to the presence of the other.

When well-controlled trials are used to answer a research question, then we can determine if one thing causes another. To determine causation, subjects in a study must be randomly assigned to either an intervention group (where the change to regular behavior is implemented) or a control group (where they don’t change a thing) and followed over time regarding all of their health behaviors to see which one is the cause and which are correlated.  Many studies that are reported on in mainstream media are not well designed to account for all activities.  For instance, you may see an article that states that weight loss improves insulin resistance in people with diabetes.  The correlation is weight loss and improved insulin resistance.  The causation can only be known when all of the other beneficial health habits like exercise, good sleep habits, and adequate fiber intake – which can all improve insulin resistance without weight loss – are accounted for.  If they are not, then the cause of the change is unknown.

In many cases, people with IBS and other GI issues like Colitis and Gastroparesis are looking for a cause to their symptoms.  It makes sense that food entering our bodies may be the cause, but food choice and GI discomfort may only be a correlation.  We know for sure that there is a correlation for those with IBS to have increased GI symptoms with highly fermentable food because there is the research to show that a Low-FODMAP Diet significantly improves symptoms for 52-86% of people with IBS.1

On to the IgG science…

  • The truth is that eating foods from the “sensitive to” list can actually indicate tolerance to the food.  In one study, the researchers concluded that the body’s response to the IgG antibody is a natural response to “foreign” substances such as food. In addition, the body’s reaction to IgG antibodies is imperative to maintaining an immunological – aka protective – response to food.2  Mind blown, right?
  • In another study done to investigate the correlation between IgG antibodies and symptoms in people with IBS, the researchers noted from their data that there was no significant correlation between symptom severity and IgG antibody levels in subjects with Irritable Bowel Syndrome.3
  • In a task force report by the European Academy of Allergy and Clinical Immunology (EAACI) this statement was made: “The presence of [IgG antibodies] against foods indicates a repeated exposure to a food treated by the immune system as an alien protein and should not be treated as a sign of hypersensitivity but rather as a marker of immune tolerance…  Specific IgG4 antibodies do not indicate a food allergy or intolerance but a physiological response to the exposure to food.”4

  • Not only did the EAACI share that the IgG Food Sensitivity Tests don’t correlate with adverse reactions to food, the American Academy of Allergy, Asthma, and Immunology (AAAAI) supported their report and added, “Serum antibody levels for [IgG antibodies] indicate the presence of specific antibody but do not make a diagnosis. The presence of [antibodies] does not indicate disease.”5 The authors also remind us that, “The improper use of certain tests to make diagnoses, in the absence of supporting clinical evidence, can lead to poor patient care and can have a serious adverse impact on patient quality of life.”5

If you suspect you have food intolerances, seek support from an Allergist and a Registered Dietitian.  If you have gastrointestinal issues, seek support from a Gastroenterologist and a Registered Dietitian.  These folks will help you to determine what foods, if any, are causing your symptoms.  There are research-based interventions like the low-FODMAP diet, as well as valid tests for food allergies and intolerances.  Don’t go it alone; we are here for you.

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