Instalab ResearchFood allergy and food sensitivity are often used interchangeably, but they represent very different biological processes. Food allergy is an immune-mediated reaction involving immunoglobulin E (IgE) antibodies. These reactions are immediate, can cause hives, swelling, and in some cases life-threatening anaphylaxis. Food allergies are diagnosed with IgE testing, skin prick testing, and oral food challenges.
Food sensitivities, often referred to as intolerances, are more complex. They may involve delayed immune responses, enzymatic deficiencies (such as lactose intolerance), or non-immune reactions altogether. Because symptoms appear hours or even days after eating and are often nonspecific, identifying food sensitivities is far more difficult. Commercial food sensitivity tests attempt to address this diagnostic gap, most commonly by measuring immunoglobulin G (IgG) antibodies.
Most commercial food sensitivity panels measure IgG or IgG4 antibodies against a list of foods using an enzyme-linked immunosorbent assay (ELISA). The assumption is that higher IgG levels mean intolerance or sensitivity to that food, which then should be eliminated from the diet. Test results often categorize foods into low, moderate, or high reactivity.
The scientific problem is that IgG antibodies are typically markers of normal exposure and tolerance, not intolerance. Multiple clinical studies have shown that healthy people with no symptoms of intolerance often have IgG antibodies to commonly eaten foods. In fact, the development of IgG is part of how the immune system learns to tolerate frequent exposures. This means a positive IgG test result is not inherently abnormal and may simply reflect a normal diet.
The strongest evidence evaluating IgG testing comes from randomized controlled trials and large clinical studies.
One of the most cited trials was conducted in patients with irritable bowel syndrome (IBS). In this randomized controlled study, 150 participants were divided into two groups. One group followed a diet excluding foods to which they had raised IgG antibodies, while the control group followed a sham diet that excluded the same number of foods, but not the IgG-positive ones. After 12 weeks, the IgG-guided diet group had a statistically significant reduction in symptom severity compared to the control group, with the greatest improvements seen in those who fully adhered to the diet. This trial suggests that in at least some conditions like IBS, IgG-based elimination may provide benefit. However, even here, the results were modest overall and highlight that such testing is far from a definitive diagnostic tool.
Outside of this trial, the clinical validity of IgG testing is much weaker. Position papers from the Canadian Society of Allergy and Clinical Immunology and the European Academy of Allergy and Clinical Immunology both emphasize that IgG tests should not be used to diagnose food allergy or intolerance. They stress that IgG antibodies reflect immune recognition and tolerance rather than adverse reactions, and that relying on these tests risks false diagnoses, unnecessary food avoidance, and even harm if patients reintroduce foods that are true allergens.
Further studies have demonstrated poor consistency across IgG testing platforms. A controlled evaluation found that the same patient could receive widely differing results depending on which IgG panel was used. This lack of reproducibility undermines confidence in the reliability of the tests.
Beyond inaccuracy, there are risks associated with misinterpreting IgG results. Patients may unnecessarily avoid healthy foods such as milk, wheat, or eggs, leading to nutritional deficiencies and reduced quality of life. Parents using these tests on children may inadvertently impose restrictive diets that stunt growth or cause malnutrition.
Even more concerning, IgG testing does not detect IgE-mediated allergies. A patient with a life-threatening peanut or shellfish allergy might test negative on an IgG panel and wrongly assume the food is safe to reintroduce. This confusion could have fatal consequences.
Despite strong warnings from experts, there is still some research suggesting a role for IgG-guided elimination in specific chronic conditions. The IBS trial is the clearest example, showing that dietary exclusion guided by IgG may reduce symptoms for some patients. Smaller studies and observational reports have suggested benefits in conditions like migraines and chronic urticaria, though these findings are less robust and often lack rigorous controls.
What this suggests is that IgG may not be a diagnostic marker of intolerance in itself, but in some patient populations, it might help guide elimination diets that reduce symptom burden. This is an important nuance. It means that while IgG tests should not be marketed as diagnostic tools for food intolerance, further controlled trials could clarify if and when they have clinical utility.
If IgG testing is unreliable, what should patients and clinicians use? The gold standard remains the elimination and reintroduction diet, ideally performed under medical supervision. This approach involves removing suspected foods for several weeks, then reintroducing them one by one while monitoring symptoms. Though time-consuming, it remains the only method that reliably establishes a causal link between food and symptoms.
