Food Sensitivity vs Food Allergy Testing: What's the Difference?

A food allergy and a food sensitivity are two different things, and the tests for them measure two different parts of your immune system. A food allergy is an IgE-mediated reaction that can come on fast and, in some cases, turn serious. A food sensitivity is usually slower and more about discomfort than danger, and the panels that claim to measure it work very differently. If you've been bloated, foggy, or wiped out after meals and you're trying to figure out which test you actually need, this is the part nobody explains well.

We'll walk through what each one is, how they're tested, and the honest truth about what a food sensitivity panel can and can't tell you. Then we'll cover how Defiant approaches testing here in Lisle.

Food Allergy vs Food Sensitivity, Side by Side

What a Food Allergy Actually Is

A food allergy is your immune system treating a harmless food like a threat. It makes IgE antibodies against something in that food, and the next time you eat it, those antibodies trigger a fast release of histamine and other chemicals. That's what causes the classic symptoms: hives, an itchy mouth, swelling, stomach pain, and in the worst cases, anaphylaxis, which affects breathing and blood pressure and needs emergency care.

Allergies are more common than a lot of people assume, and they're also over-assumed. In a survey of more than 40,000 US adults, about 10.8% had a convincing food allergy, while close to 19% believed they were allergic to something.⁵ That gap matters. Plenty of people who react to a food aren't actually allergic to it, which is exactly why the type of test you run makes such a difference.

What a Food Sensitivity or Intolerance Is

A food sensitivity, or intolerance, is a reaction that doesn't involve IgE and usually isn't an emergency. The most familiar example is lactose intolerance, where your body lacks enough of the enzyme to break down the sugar in dairy, so you get gas, bloating, and cramping a few hours later. Other people react to things like gluten, certain FODMAP carbohydrates, histamine-rich foods, or additives.

The symptoms tend to be digestive, but not always. Some people notice headaches, low energy, or that heavy, foggy feeling after certain meals. Because the reaction is delayed and the symptoms are vague, sensitivities are genuinely hard to track down, and that's part of why food sensitivity panels have gotten so popular. People want a shortcut to the answer. The honest version is that the shortcut isn't as clean as the marketing suggests.

How Each One Gets Tested

For a suspected food allergy, an allergist typically starts with a skin prick test or a blood test that measures IgE antibodies to specific foods. Those tests are useful, but on their own they can flag foods you actually tolerate, so a positive result isn't the final word. When the picture is unclear, the gold standard is a supervised oral food challenge, where you eat gradually increasing amounts of the food under medical watch to confirm or rule out a real allergy.⁴

Food sensitivity testing usually looks different. Most direct-to-consumer sensitivity panels measure IgG (sometimes IgG4) antibodies against a long list of foods, often a hundred or more at once. You give a blood sample, and a couple weeks later you get a color-coded report ranking foods from green to red. It looks scientific and satisfying. What it's measuring, though, is worth understanding before you cut out half your diet based on it.

The Honest Part: What IgG Testing Can and Can't Tell You

Here's the piece most clinics won't say out loud: the major allergy organizations don't recommend IgG food testing to diagnose an allergy or an intolerance. The American Academy of Allergy, Asthma & Immunology puts it plainly, noting there's no solid evidence that IgG antibodies reliably indicate a food allergy or sensitivity, and that a high IgG level to a food is often a normal sign you eat it and tolerate it just fine.¹ The European Academy of Allergy and Clinical Immunology reached the same conclusion in a task force report, stating that testing for IgG4 against foods should not be used as a diagnostic tool.² The Canadian Society of Allergy and Clinical Immunology has published a matching position.³

So does that make an IgG panel useless? Not exactly, and this is where it gets nuanced. A sensitivity panel can't hand you a diagnosis, but it can give you and a provider a shortlist of foods to look at more carefully. Think of it as a hypothesis, not a verdict. The results are only meaningful when a person who knows what they're doing helps you test them against how you actually feel. On its own, a red square on a report isn't a reason to fear a food for life.

How to Actually Use a Food Sensitivity Panel

The real diagnostic tool for food sensitivities is still the oldest one: a structured elimination and reintroduction plan. You remove the suspect foods for a few weeks, track how you feel, then add them back one at a time and watch for symptoms. It takes patience, but it tells you something an antibody number can't, which is whether that food actually bothers your body.

This is where a panel earns its keep. Trying to eliminate every food at once is miserable and unrealistic, so a sensitivity report can narrow a huge list down to a handful worth testing first. From there, the work is behavioral rather than lab-based. If you've already tried cutting out the obvious suspects and you're still stuck, that's usually the point where testing plus a provider's help beats guessing on your own.

How Testing Works at Defiant

At Defiant, we offer three panels, and we're upfront about what each one is for. The Food Sensitivity Panel measures IgG across 250 foods and runs $300. The Allergy Test measures IgE across 150 allergens for $200. The Combo Panel covers both, IgG plus IgE across 250 markers, for $400. Results generally come back in one to two weeks, and we sit down with you to go over them and build the elimination or reintroduction plan around what they show.

One operational note that trips people up: we don't draw blood in the clinic. We write the lab order, and you complete the draw through your primary care provider or through Rythm Health, our lab partner. Using our Rythm Health referral link saves you $20 on the draw. If your main goal is ruling in or out a true allergy, an allergist and an IgE-based workup are the right path. If you're chasing down vague digestive or energy symptoms and want a smarter starting point than trial and error, that's exactly what the sensitivity work is built for. You can see the full menu on our Diagnostic Testing page. We serve Lisle, Naperville, Downers Grove, Wheaton, and Chicago's western suburbs.

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Last updated August 6, 2026.