I get asked about food sensitivity testing almost every week in clinic, and honestly, it’s usually the same scene. Someone walks in holding a printout from an online kit, a long list of “reactive” foods circled in red pen, looking almost relieved. Like they’ve finally cracked the case. I get it, I really do. Bloating, fatigue, that foggy head feeling, random skin flare-ups- it wears you down when nobody can tell you why. But before you start throwing foods out of your fridge based on one of these results, it’s worth slowing down and asking what the test is actually measuring. Because it’s probably not what you think.
What Does Food Sensitivity Testing Actually Test?
Most of these kits measure something called IgG antibodies against a huge list of foods, sometimes over a hundred. The pitch sounds convincing enough. High IgG to a food means your body’s reacting badly to it, so cut it out, right?
Not quite. IgG antibodies show up as a totally normal part of eating. Your immune system produces them when it’s seen a food protein again and again, which usually just means it’s something you eat a lot, not something that’s making you ill. I dug into this properly in my post on IgG vs IgE and how immune testing actually works, because honestly the two get mixed up constantly and it causes a lot of unnecessary worry.
Why the Science Doesn’t Really Back Most of These Kits
So what does the evidence actually say?
- IgG tells you what you’ve eaten, not what’s hurting you: People show elevated IgG to foods they eat all the time, symptoms or no symptoms.
- The major allergy and gut health bodies don’t recommend it: The European Academy of Allergy and Clinical Immunology has come out and said, plainly, don’t use IgG testing to diagnose intolerance.
- The labs don’t even agree with each other: Send the same blood twice to two different companies and don’t be surprised if you get two different food lists back.
- Cutting foods out on this basis can actually make things worse: I’ve seen it lead to nutrient gaps, and sometimes tip people into eating patterns that aren’t healthy at all.
None of that means what you’re feeling isn’t real. It’s just that the test people are using to explain it usually isn’t up to the job.
True Food Intolerance vs What These Kits Claim
A few terms get thrown around loosely in my clinic, and it helps to actually pull them apart:
- Food allergy is an immediate immune reaction driven by IgE (think hives, swelling, anaphylaxis). This is one you can genuinely test for, through skin prick tests or specific IgE blood work.
- Food intolerance isn’t immune-related at all, it’s more mechanical, like lacking the enzyme to break down lactose.
- Sensitivity is the tricky one. There’s no agreed medical definition for it, which is a big part of why it’s so hard to test for in the first place.
A lot of my patients who are convinced they have a hidden food intolerance actually have something like IBS sitting underneath it all. If that sounds familiar, take a look at my piece on how IBD and IBS differ in causes and diagnosis.
What Actually Works Instead
If you genuinely think a food is behind your symptoms, here’s what I tend to suggest before anyone reaches for a test kit:
- Start a food and symptom diary and stick with it for a couple of weeks before you change anything. Patterns tend to show themselves once you’re actually writing things down.
- Try a proper elimination and reintroduction plan, with a dietitian if you can, rather than cutting five things out at once and hoping for the best.
- Rule out the conditions that mimic sensitivity: coeliac disease, lactose intolerance, fructose malabsorption. These all have real, validated tests behind them.
- Look into a low FODMAP approach if bloating and unpredictable bowel habits are your main complaint. There’s decent trial evidence for this one.
- Ask about breath testing for specific carbohydrate intolerances instead of a broad antibody panel that isn’t really telling you anything specific.
Is Any of This Testing Worth Doing?
To be fair, there are a few situations where structured testing genuinely earns its place:
- Coeliac disease screening with tTG-IgA blood tests
- Hydrogen breath testing for lactose or fructose intolerance
- Skin prick or specific IgE testing when a true allergy is on the table
What I wouldn’t do is spend money on a broad IgG panel expecting it to explain chronic gut symptoms. In my experience it rarely does, and it often nudges people toward restriction that doesn’t fix the actual problem underneath.
A Note from My Own Practice
I’ve had patients cut out whole food groups for months, sometimes longer, all based on one test result. And their symptoms just… didn’t change. Not really. When we went back to basics, a proper diary, a low FODMAP trial where it made sense, the real culprit was usually something the original test hadn’t even flagged. I’ve seen this play out often enough that it’s shaped how I approach it now. A structured plan beats a single blood draw, every time.
The Bottom Line
Food sensitivity testing sold through commercial IgG kits just doesn’t hold up under scrutiny, and leaning on it can send you down a path of restriction you probably didn’t need. If your gut symptoms have been hanging around, you’re better served by proper diagnostic steps: ruling out coeliac disease, checking for real intolerances, and trying a guided elimination diet if needed. Knowing the difference between the food sensitivity testing you see advertised online and the medically validated testing that actually exists is the first real step toward getting answers you can trust. It’s the approach I take with every patient who sits across from me asking this exact question.
Want more of this kind of honest, evidence-based breakdown? Have a listen to the Liver & Guts Podcast, I go through topics like this one all the time.
And if your symptoms have gone unexplained for too long, don’t just keep guessing. Book a consultation and let’s actually get to the bottom of it.
