Understanding the Immune System: IgG, IgE, IgA, and IgM in Food Sensitivities & GI Health
Introduction
When people experience symptoms like bloating, fatigue, skin issues, or brain fog, they often look to food sensitivity testing for answers. But interpreting these tests properly requires a deeper understanding of how different parts of the immune system work. The immune system is a complex network, and various antibody types — like IgG, IgA, IgE, and IgM — each play distinct roles in how the body responds to foods, microbes, and inflammation.
Let’s discuss the nuances between these antibodies, how they relate to food reactivity, and why functional stool testing like the GI-MAP® can provide essential context for interpreting immune response lab profiles.
Breaking Down the Immune Response: The Roles of IgG, IgA, IgE, and IgM
- IgG (Immunoglobulin G): IgG is the most abundant antibody in circulation and is often measured in food sensitivity tests like the IgG Food Explorer™ from Diagnostic Solutions Laboratory. IgG responses reflect delayed hypersensitivity to foods, meaning symptoms may appear hours or even days after eating a trigger food. These antibodies may indicate past or ongoing exposure and potential inflammation, but their presence alone does not always mean a food needs to be eliminated completely. Instead, patterns and symptom correlation matter most.
- IgE (Immunoglobulin E): IgE antibodies are responsible for immediate allergic reactions (e.g., hives, anaphylaxis, itching, swelling). These reactions are fast and often severe, and they involve mast cells and histamine release. IgE antibody profiling is best used when there is a suspected classic food allergy, and the IgE Allergy Explorer™ is a comprehensive IgE panel also available through Diagnostic Solutions Laboratory.
- IgA (Immunoglobulin A): IgA plays a key role in mucosal immunity and is the body’s first line of defense in the gut, respiratory tract, and urogenital lining. Elevated or depleted IgA (especially secretory IgA, or SIgA) can signal gut inflammation, infection, or loss of tolerance to antigens including food proteins. IgA responses are especially helpful in identifying chronic mucosal stress. Assessing SIgA on the GI-MAP along with food immune profiling provides more immune insights than the blood panel alone.
- IgM (Immunoglobulin M): IgM is the first antibody the body produces in response to a new threat. It typically represents recent or acute exposure and provides short-term defense before IgG takes over. Though less commonly tested in food panels, it may provide insight into current immune activation or infection.
Why IgG Food Sensitivity Testing Isn’t the Whole Story
IgG food sensitivity testing, like the IgG Food Explorer, can be useful in uncovering foods the immune system may be reacting to, but it's important to understand it is not diagnostic on its own. Elevated IgG to a food may simply reflect high consumption, poor digestion, or leaky gut. It does not always mean a food is "bad" for you or must be permanently eliminated. Instead, this information should be combined with:
- Clinical history and symptoms
- Diet and food exposure
- Gut integrity and enzyme function
According to the IgG Food Explorer Interpretive Guide (pages 7–8), patterns are more important than isolated high markers. For instance, a cluster of elevated IgG markers to dairy (casein, whey, cow's milk) is more meaningful than one mildly reactive food. This approach helps guide short-term elimination and longer-term healing strategies.
The Missing Piece: What the GI-MAP Stool Test Adds
To truly understand food sensitivities, we must also ask why the immune system is reacting in the first place. That’s where the GI‑MAP stool test offers critical insight.
- EAP (Elastase-Associated Protein): This marker reflects pancreatic enzyme output. If low, it suggests poor digestion and absorption of nutrients — especially proteins. Undigested proteins can cross a compromised gut barrier and trigger immune responses, including elevated IgG antibodies.
- SIgA (Secretory IgA): SIgA is the immune system's front line in the gut. Low SIgA may reflect immune exhaustion or suppressed mucosal immunity, while elevated SIgA can indicate chronic irritation or infection. In either case, the ability to tolerate foods (oral tolerance) may be reduced.
- Zonulin: Zonulin regulates the tight junctions in the gut wall. Elevated levels suggest intestinal permeability or "leaky gut," which increases the likelihood that food particles or pathogens pass through the gut lining and provoke the immune system.
When SIgA is low and zonulin is high, it signals a breakdown in the body’s ability to tolerate harmless food antigens, often leading to IgG elevations. In this state, even nutrient-dense foods may provoke symptoms.
Putting It All Together: A Root Cause Approach to Food Sensitivities
Rather than viewing IgG food results in isolation, a functional approach asks:
- Is the immune system reacting because the gut barrier is compromised?
- Are there underlying infections or inflammation triggering immune responses?
- Is poor digestion contributing to food protein exposure?
Using both the IgG Food Explorer™ and GI-MAP® stool test together allows providers to better understand not just what the body is reacting to, but why. This leads to more targeted dietary interventions, strategic gut healing protocols, and ultimately, restored oral tolerance.
Conclusion
A Functional Perspective on Immune-Mediated Food Reactions
Food sensitivities are real, but they're also often a symptom of a deeper issue. By assessing the immune system holistically — looking at IgG, IgA, IgE, and IgM alongside gut health markers like EAP, SIgA, and zonulin — we gain the clarity needed to move beyond food elimination and into true healing.
For patients struggling with chronic symptoms, your ability to interpret these tests together can uncover root causes and help them rebuild a healthier relationship with food from the inside out.
Author Greer McGuinness, MS, RD, CDN, CLT
Greer McGuinness, MS, RD, CDN, CLT, holds a Master of Science in Nutrition and Dietetics and is a Registered Dietitian, Certified Detox Specialist, Certified Master Herbalist, Certified Lyme Specialist, and Certified Mental Health Specialist. Greer is a member of the Clinical Team at Diagnostic Solutions Laboratory and is passionate about teaching practitioners how to use functional medicine testing to optimize outcomes for their patients.
Greer has made significant contributions to the field of pediatric health. Her expertise lies in detoxifying toxins, enhancing gut health, and optimizing nutrient status. As a published researcher, she has focused on autism spectrum disorder (ASD) and alternative medicine, showcasing her commitment to exploring innovative approaches to healthcare.
Greer is the proud owner of Biomedical Healing for Kids, a virtual private practice in New York.
The opinions expressed in this presentation are the author's own. Information is provided for informational purposes only and is not meant to be a substitute for personal advice provided by a doctor or other qualified health care professional. Patients should not use the information contained herein for diagnosing a health or fitness problem or disease. Patients should always consult with a doctor or other health care professional for medical advice or information about diagnosis and treatment.