Food Sensitivity Testing: What Works What Doesn't and What Your Doctor Won't Tell You

Food Sensitivity Testing: What Works, What Doesn't, and What Your Doctor Won't Tell You

By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante

The Difference Between Allergy, Intolerance, and Sensitivity

These three terms are used interchangeably in popular culture, but they represent completely different biological mechanisms:

Food Allergy (IgE-Mediated)

This is a true immune response. The immune system produces IgE antibodies against specific food proteins, triggering mast cell degranulation and histamine release. Symptoms occur within minutes to hours: hives, swelling, difficulty breathing, anaphylaxis. This is testable (skin prick tests, serum IgE), reproducible, and potentially life-threatening. Managed by strict avoidance and epinephrine auto-injectors. Affects 4-8% of children and 3-4% of adults.

Food Intolerance (Enzyme-Based)

The body lacks an enzyme needed to digest a specific food component. The classic example: lactose intolerance (deficiency of lactase enzyme). The undigested substrate causes symptoms through osmotic effects and fermentation — bloating, gas, diarrhea. This is dose-dependent (small amounts may be tolerated), reproducible, and testable (breath tests for lactose, fructose). Other examples: histamine intolerance (DAO deficiency), fructose malabsorption.

Food Sensitivity (The Controversial Category)

This is where the science gets murky. Food sensitivities are real in the sense that patients consistently experience symptoms from certain foods. However, the immune mechanism is poorly understood and the commercial tests claiming to identify them are not validated.

Why IgG Food Sensitivity Tests Are Unreliable

Companies like Everlywell, Viome, YorkTest, and ALCAT offer blood tests that measure IgG antibodies to 100+ foods and claim to identify your "food sensitivities." These tests are problematic for several fundamental scientific reasons:

1. IgG Reflects Exposure, Not Sensitivity

IgG antibodies are a NORMAL part of the immune response to food. Eating a food regularly increases IgG antibodies to that food. This is immune tolerance, not immune reaction. The American Academy of Allergy, Asthma & Immunology (AAAAI) has explicitly stated that IgG4 to foods "indicates the person has been exposed to the food repeatedly and has developed tolerance."

2. Poor Reproducibility

Studies have shown that the same blood sample sent to the same lab under different names produces different results. Test-retest reliability is poor — the gold standard requirement for any valid diagnostic test.

3. No Medical Organization Endorsement

The AAAAI, the European Academy of Allergy and Clinical Immunology (EAACI), the Canadian Society of Allergy and Clinical Immunology, and the Australasian Society of Clinical Immunology and Allergy have all published position statements AGAINST using IgG testing for food sensitivity diagnosis.

4. Potential for Harm

These tests frequently flag 20-40 foods as "reactive," leading patients to unnecessarily restrict their diets. Extreme dietary restriction can cause nutritional deficiencies, eating disorders, reduced microbiome diversity (from reduced dietary diversity), and significant quality-of-life impairment.

What Actually Works: Validated Testing Methods

1. Elimination Diet (Gold Standard)

The elimination diet remains the most reliable method for identifying food sensitivities. The process:

1. Elimination phase (2-6 weeks): Remove suspected trigger foods (or follow a structured protocol like low FODMAP)
2. Symptom monitoring: Track symptoms daily. If symptoms improve significantly, food triggers are likely among the eliminated foods.
3. Reintroduction phase: Add back one food group at a time, every 3-7 days, while monitoring symptoms. A clear symptom return upon reintroduction = confirmed trigger.

For IBS patients specifically, the low FODMAP elimination diet is the most evidence-based approach. A Cochrane review confirmed that low FODMAP diet reduces IBS symptoms in 50-86% of patients. The structured Monash University reintroduction protocol then identifies which specific FODMAP groups are triggers for each individual.

2. Hydrogen/Methane Breath Tests (Validated)

• Lactose breath test: Confirms lactose intolerance with high sensitivity and specificity
• Fructose breath test: Identifies fructose malabsorption
• Lactulose/glucose breath test: Screens for SIBO

3. Skin Prick Test and Serum IgE (For True Allergies)

These are validated, reproducible, and endorsed by all allergy organizations for IgE-mediated food allergies. Appropriate for suspected allergic reactions (hives, swelling, anaphylaxis), NOT for GI-only symptoms like bloating and gas.

4. Celiac Testing

Tissue transglutaminase IgA (tTG-IgA) with total IgA level is the standard screening test for celiac disease. Celiac is a real, immune-mediated condition with validated testing. Anyone with persistent GI symptoms should be screened before starting a gluten-free diet.

A Practical Approach to Finding Your Triggers

1. Rule out serious conditions first: Celiac screen, basic bloodwork, consider colonoscopy if red flag symptoms are present
2. Start a low FODMAP elimination under guidance (Monash app or FODMAP-trained dietitian)
3. Take Casa de Sante Digestive Enzymes with meals during and after the elimination phase to optimize digestion and reduce confounding variables
4. Reintroduce systematically — one FODMAP group at a time, 3-day challenges
5. Consider breath testing for lactose, fructose, and SIBO if the elimination diet is inconclusive
6. Track everything — food diary with symptom scores for 4-8 weeks reveals patterns that memory alone cannot

Frequently Asked Questions

My IgG test showed I'm sensitive to 30 foods. Should I avoid them all?

No. Eliminating 30 foods based on an unvalidated test is nutritionally dangerous and likely unnecessary. Instead, use an evidence-based elimination diet to identify your actual triggers, which are typically 3-5 foods, not 30. The IgG results most likely reflect the foods you eat most frequently.

Are microbiome tests (Viome, etc.) useful for food sensitivity?

Current microbiome testing can provide interesting information about your microbial composition, but the dietary recommendations derived from these tests are not yet validated in clinical trials. The science of translating microbiome data into personalized dietary advice is promising but still in early stages.

Can food sensitivities change over time?

Yes. Food sensitivities are often temporary, reflecting current gut health status rather than permanent conditions. Healing the gut barrier, restoring the microbiome, and resolving SIBO can eliminate sensitivities that seemed permanent. This is why periodic reintroduction testing is recommended — foods that triggered symptoms 6 months ago may be tolerated now.