What Is MRT Food Sensitivity Testing — and How Is It Different From IgG Testing?

If you've spent time researching food sensitivities, you've likely come across two very different types of tests: IgG panels and the Mediator Release Test (MRT). Both claim to identify foods that may be contributing to your symptoms. But they work through entirely different mechanisms — and the clinical outcomes they produce are not the same.

Understanding the distinction matters, because the test you choose doesn't just identify reactive foods. It shapes the entire dietary strategy that follows. And for people dealing with chronic symptoms like migraines, IBS, fatigue, skin conditions, joint pain, or brain fog, choosing the right approach can mean the difference between meaningful improvement and continued frustration.

What Is a Food Sensitivity — and Why Is It Different From a Food Allergy?

Before comparing tests, it helps to understand what a food sensitivity actually is.

A classic food allergy involves an IgE-mediated immune response — the kind that causes immediate, sometimes life-threatening reactions like hives, throat swelling, or anaphylaxis. These reactions are fast, dramatic, and relatively easy to identify.

Food sensitivities are different. They involve delayed immune reactions that can occur hours or even days after eating a reactive food. Because the response is slow and diffuse, it is rarely obvious which food is responsible. Symptoms can appear anywhere in the body — not just the digestive tract — because the underlying mechanism is systemic inflammation, not a localized allergic response.

This is one of the most important and least understood aspects of food sensitivities: they are not primarily a gut issue. They are an immune issue that happens to affect the gut, the brain, the skin, the joints, the sinuses, and virtually any other tissue in the body. When the immune system is chronically activated by food triggers, the resulting inflammatory mediators circulate throughout the bloodstream and can drive symptoms in multiple systems simultaneously.

How IgG Food Sensitivity Testing Works

IgG testing measures the presence of IgG antibodies — a class of immunoglobulin — to specific foods in the blood. The premise is that elevated IgG antibodies to a food indicate immune reactivity and potential sensitivity.

IgG panels are widely available, relatively inexpensive, and often return long lists of reactive foods — sometimes 30, 40, or even 60 items. For many people, this creates more confusion than clarity. Which foods are truly driving symptoms? Which are incidental? How do you build a sustainable diet around a list that long?

There is also a more fundamental scientific concern: IgG antibodies are a normal part of the immune system's response to food. They are produced as part of oral tolerance — the process by which the immune system learns to recognize and accept foods as safe. Elevated IgG to a food may simply reflect frequent exposure, not pathological reactivity. Several major allergy and immunology organizations have noted that IgG testing has not been validated as a reliable clinical tool for identifying foods that cause symptoms.

This does not mean IgG testing is without value in every context. But it does mean that a long list of IgG-reactive foods is not the same as a clinically validated list of foods that are actively driving your inflammation.

How the Mediator Release Test (MRT) Works

The Mediator Release Test takes a fundamentally different approach. Rather than measuring antibodies to specific foods, MRT measures the end result of immune activation — the release of inflammatory mediators from white blood cells.

When the immune system reacts to a food or food chemical, white blood cells release mediators: histamine, cytokines, prostaglandins, leukotrienes, and other inflammatory compounds. These mediators are what actually cause symptoms. MRT measures the degree to which white blood cells shrink (releasing their contents) when exposed to 170 different foods and food chemicals. The greater the volume change, the more significant the immune response.

This approach captures a broader spectrum of immune reactivity than antibody-based tests. It detects reactions mediated by IgG, IgM, IgA, T-cells, and other pathways — not just one antibody class. It also tests food chemicals (like salicylates, amines, and glutamates) that antibody panels typically miss, even though these compounds are among the most common drivers of food-related symptoms.

The result is a quantitative reactivity score for each food and chemical, ranked from least to most reactive. This ranking is not just informational — it is the foundation of the dietary strategy that follows.

The LEAP Protocol: Starting With Your Least Inflammatory Foods

This is where MRT diverges most significantly from IgG testing — not just in the science of the test itself, but in the philosophy of what happens next.

Most elimination approaches, including those based on IgG results, focus on removing reactive foods. The LEAP (Lifestyle Eating and Performance) protocol takes the opposite starting point: rather than beginning with what to eliminate, it begins with what is safe.

The reasoning is grounded in how the immune system heals. When someone has been chronically exposed to multiple food triggers, the immune system is in a state of persistent activation. The gut lining is often compromised. Inflammation is systemic. In this state, the body has limited capacity to tolerate new exposures — even foods that are not highly reactive can provoke a response simply because the system is overwhelmed.

LEAP begins with the 10–15 foods that tested least reactive on the MRT. These become the foundation of the initial diet — a narrow, highly tolerated eating plan that gives the immune system the space it needs to quiet down. As inflammation resolves and symptoms improve, foods are systematically reintroduced in order of reactivity, from least to most. This structured reintroduction allows the body to identify true triggers clearly, without the noise of a chronically inflamed baseline.

The goal is not a permanent restricted diet. The goal is a temporary period of immune calm that allows the body to heal — and then a gradual return to a broader, sustainable way of eating with a clear understanding of individual tolerances.

Why Food Sensitivities Are Rarely Just a Gut Issue

One of the most common misconceptions about food sensitivities is that they primarily cause digestive symptoms. In clinical practice, this is often not the case.

Because the inflammatory mediators released during a food sensitivity reaction circulate systemically, they can drive symptoms in virtually any tissue. Clients come in describing migraines that have never responded to conventional treatment, skin conditions like eczema or psoriasis that flare unpredictably, joint pain with no clear structural cause, chronic fatigue that persists despite adequate sleep, anxiety or mood instability that worsens after certain meals, and sinus congestion or post-nasal drip that has been attributed to allergies for years.

In many of these cases, food sensitivities are a significant contributing factor — not because the food is "bad," but because that individual's immune system has developed a reactive pattern to it. Once the reactive foods are identified and removed during the initial LEAP phase, the reduction in systemic inflammatory load can produce improvements across multiple symptom categories simultaneously.

This is also why MRT is most effective when paired with a gut healing protocol. Intestinal permeability — often called leaky gut — is both a consequence of chronic food reactivity and a driver of it. When the gut lining is compromised, partially digested food proteins pass into the bloodstream more readily, increasing the likelihood of immune activation. Addressing the gut barrier alongside the dietary changes creates a more complete and durable resolution of symptoms.

Who Is MRT Testing Best Suited For?

MRT and the LEAP protocol tend to produce the most meaningful results for people who have been dealing with chronic, multi-system symptoms that have not responded fully to conventional approaches. This includes individuals with:

Irritable bowel syndrome (IBS), chronic diarrhea, constipation, or bloating that persists despite dietary changes. Migraine headaches, particularly those that seem to be triggered by food but where the specific triggers have been difficult to identify consistently. Inflammatory skin conditions including eczema, psoriasis, urticaria, and acne that have a dietary component. Fibromyalgia or chronic widespread pain with no clear structural explanation. Autoimmune conditions where dietary inflammation may be contributing to flare frequency or severity. Chronic fatigue, brain fog, or mood instability that correlates with eating patterns. Children and adults with ADHD or behavioral concerns where food chemicals may be a contributing factor.

MRT is not a diagnostic test for disease. It is a clinical tool that helps identify dietary contributors to inflammation — one piece of a comprehensive functional assessment that also considers gut health, nutrient status, toxic burden, stress, sleep, and other root cause factors.

What to Expect From the Process at Innovative Nutrition

The MRT process begins with a blood draw, which is sent to Oxford Biomedical Technologies — the laboratory that developed and validates the MRT. Results are typically returned within 7–10 business days and include a detailed reactivity report for all 170 foods and chemicals tested.

Results are reviewed together in a dedicated session. Rather than handing over a list and leaving you to figure out the rest, the review session is used to build your personalized LEAP diet — identifying your initial safe foods, mapping out the reintroduction sequence, and addressing practical questions about meal planning, dining out, and navigating the transition.

Ongoing support is available throughout the LEAP process, because the reintroduction phase requires careful attention and adjustment. Most clients begin to notice meaningful symptom improvement within the first two to four weeks of the initial LEAP diet, with continued progress as the reintroduction proceeds.

For clients with significant gut involvement, MRT is often paired with a GI Map stool analysis and, in some cases, the Advanced Intestinal Barrier Assessment (AIBA) to evaluate intestinal permeability directly. Addressing the gut alongside the dietary changes produces more complete and lasting results than either intervention alone.

If you have been living with chronic symptoms and have not found clear answers through conventional testing, MRT food sensitivity testing may offer the missing piece. A free 15-minute discovery call is available to discuss whether this approach is a good fit for your situation.