What are the signs and symptoms of IgG (Immunoglobulin G) food sensitivity?

Signs and Symptoms of IgG Food Sensitivity

IgG food sensitivity is not a validated clinical entity according to current medical guidelines, and IgG testing for food sensitivities is not recommended for diagnosis of food allergies or intolerances. 1

Understanding Food Reactions: IgE vs. Non-IgE Mechanisms

Food reactions can be categorized into different immunological mechanisms:

IgE-Mediated Food Allergies

• Timing: Immediate reactions (minutes to 2 hours after ingestion) 1
• Common symptoms: Urticaria, angioedema, respiratory symptoms, anaphylaxis 1
• Diagnosis: Validated through skin prick tests and serum-specific IgE testing 2

Non-IgE and Mixed Mechanism Reactions

• Timing: Delayed reactions (hours to days) 1
• Presentation: More chronic symptoms, often gastrointestinal 1
• Examples: Eosinophilic esophagitis (EoE), food protein-induced enterocolitis syndrome (FPIES) 1

Purported Signs and Symptoms of IgG Food Sensitivity

While IgG food sensitivity testing is commercially available, major allergy organizations do not support its use. However, patients who pursue IgG testing often report these symptoms:

Gastrointestinal Symptoms

• Abdominal pain
• Bloating
• Diarrhea
• Nausea
• Vomiting
• Constipation

Extra-intestinal Symptoms

• Headaches/migraines
• Fatigue
• Skin rashes (non-urticarial)
• Joint pain
• Brain fog

Evidence Against IgG Testing for Food Sensitivity

The NIAID-sponsored expert panel guidelines explicitly state that many adverse reactions to foods are misclassified as allergic in origin 1. Studies examining IgG testing in irritable bowel syndrome have found:

• Positive skin tests and IgG serum antibodies are not reliable indicators of food hypersensitivity 3
• Food challenges in patients with positive IgG tests often do not reproduce symptoms 3
• Up to 35% of individuals report reactions to food, but only about 3.5% have confirmed food allergy by oral food challenge 1

Alpha-Gal Syndrome: A Special Case

Alpha-Gal syndrome represents a unique delayed IgE-mediated food allergy that may be confused with IgG sensitivity:

• Mechanism: IgE antibodies to galactose-alpha-1,3-galactose (alpha-gal) 1, 4
• Timing: Delayed reactions (3-5 hours after mammalian meat consumption) 4
• Symptoms: Abdominal pain, nausea, vomiting, diarrhea, with or without skin manifestations 1, 4
• Cause: Sensitization occurs after tick bites, particularly from Lone Star ticks 1, 4

Clinical Approach to Suspected Food Reactions

When patients present with symptoms attributed to food sensitivity:

1. Rule out true IgE-mediated food allergy

   • Immediate reactions
   • Reproducible symptoms
   • Consider skin prick testing or serum-specific IgE

2. Consider non-IgE mediated disorders

   • FPIES, EoE, celiac disease
   • Alpha-gal syndrome if delayed reactions to mammalian meat

3. Evaluate for non-immunologic food reactions

   • Lactose intolerance
   • FODMAP sensitivity
   • Food additives/chemical sensitivities

4. Consider functional GI disorders

   • Irritable bowel syndrome
   • Functional dyspepsia

Important Caveats

• The presence of food-specific IgG antibodies is often a normal physiological response to food exposure and does not necessarily indicate pathology 1
• Commercial IgG food sensitivity tests have not been validated for diagnosis of food allergies or intolerances 1
• Elimination diets based solely on IgG testing may lead to unnecessary dietary restrictions and potential nutritional deficiencies

In conclusion, while patients may attribute various symptoms to IgG food sensitivities, current medical evidence does not support IgG testing for diagnosis of food allergies or intolerances. Patients with suspected food-related symptoms should undergo proper evaluation for validated food-related disorders.