Food Intolerance Tests: What You Need to Know
- The London Allergy Clinic
- Oct 2, 2025
- 3 min read
Updated: Feb 20
What’s the difference between food allergy vs food intolerance?
Many people use “allergy” and “intolerance” interchangeably, but they are distinct. A food allergy involves your immune system reacting (often via IgE antibodies) to a normally harmless food protein. Symptoms can be severe including life-threatening anaphylaxis.
Food intolerance, by contrast, does not involve the immune system—it’s usually a delayed reaction, dose-dependent, often affecting digestion (e.g. lactose intolerance). Symptoms usually are associated with the gut and can include IBS-type symptoms and reflux. Usually, these symptoms are less severe than those associated with allergy.
The key difference in testing methods between the two is that allergy tests (specific IgE) are clinically validated, whereas the vast majority of food intolerance tests are not.
Most tests which claim to investigate food intolerance are IgG tests, but this is not reliable and can lead to dangerous misdiagnoses and unnecessary dietary restrictions (see more below).
We provide evidence-based testing methods only and therefore we do not offer any "food intolerance" or "sensitivity" tests.
Recognised allergy tests: IgE, skin prick, and oral challenge
There are validated, evidence-based tests for diagnosing food allergy. For IgE-mediated allergic reactions, clinicians use skin prick testing or specific IgE blood tests as first-line assessments.
Test results must always be interpreted alongside the clinical history, because testing alone does not give a definitive diagnosis. False positives or false negatives are possible.
The true “gold standard” remains the oral food challenge, where the patient is exposed to the suspected food under careful medical supervision to see whether symptoms occur.
For clarity, the following are common points of confusion:
- Lactose intolerance is not an allergy and will not show on an allergy test.
- Gluten intolerance is also not an allergy and will not show on an allergy test.
Milk allergies and wheat allergies are real, but they are not the same as lactose intolerance or gluten intolerance.
Coeliac disease or IBS are also not allergies, and will not show on an allergy test.
Is there is no reliable test for food intolerance?
Unlike food allergy, no validated laboratory test exists for most forms of food intolerance or non-immune mediated food hypersensitivity.
As BSACI warns, "Alternative testing has no proven benefit in the diagnosis of food allergy and food intolerance. This may endanger patients via misdiagnosis.”
Read more here: https://www.bsaci.org/wp-content/uploads/2020/02/Choosing-wisely-ALTERNATIVE-TESTS.pdf
Diagnosing intolerance (for example lactose or fructose intolerance) is typically based on symptom history, tolerance testing (e.g. hydrogen breath tests for lactose), and controlled dietary trials.
IgG testing, “hair analysis” or other alternative tests are not clinically used and are not considered reliable.
The problems with IgG food intolerance testing
One of the most common “tests” marketed to patients is IgG food antibody testing. But this is scientifically flawed: The BSACI notes that “the presence of IgG antibodies does NOT indicate an allergy or intolerance to a specific food. IgG antibodies to food are formed in all healthy asymptomatic people.”
The British Dietetic Association (BDA) also states there is no convincing evidence to support the use of IgG testing as a diagnostic tool. Such tests can generate misleading results, causing patients to exclude many foods unnecessarily.
Risks of unnecessary elimination diets
Removing foods from your diet without a clear, evidence-based reason carries real risks. Nutritional deficiencies can result, especially in children.
Moreover, if a patient does have a genuine allergic sensitisation, elimination of foods that they previously tolerated may reduce their tolerance and increase the risk of developing a severe reaction when re-exposed.
Inappropriate elimination diets can also increase anxiety, social burden, and the cost and complexity of meals.
How to choose wisely: evidence-based evaluation
When suspecting a reaction to food, the correct approach is a detailed clinical history by a qualified allergy professional, focusing on timing, symptoms, dose relation, and reproducibility. Then validated tests (IgE / skin prick) can be ordered when indicated.
Alternative or “novel” tests like hair analysis, kinesiology, bio‐resonance, Vega testing, atopy patch tests, leucocyte cytotoxic tests, and others “are not valid diagnostic tests for any type of food allergy.” BSACI
How we can help at the London Allergy Clinic
At the London Allergy Clinic, we don’t sell gimmicks. We provide evidence-based evaluation: clinical assessment, validated allergy testing when appropriate, and structured challenge-based diagnosis. If you’ve tried an intolerance test and are left confused or restricted, we can help you re-establish clarity, restore nutritional balance, and guide you safely.
Our team of expert professionals can guide you through this process.
Next Steps
If you are concerned about allergy, it is advisable to seek a specialist advice and appropriate testing.
Our team at The London Allergy Clinic is available to advise on diagnosis, testing and management.
Contact us to arrange an appointment.
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