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Science Weekly

What is a food intolerance, and how do you know if you have one?

28 Apr 2026

Transcription

Transcript generated automatically by AI and may contain errors.

Chapter 1: What is a food intolerance and how does it differ from an allergy?

0.031 - 23.897 Madeleine Finlay

This is The Guardian. Sat in her kitchen, surrounded by tiny tubes, envelopes and disposable needles, food and health writer Rebecca Seal decided to run an experiment.

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24.438 - 32.012 Rebecca Seal

I lined them all up on the table. I thought the best way of doing it scientifically, although obviously I'm a study of one, was to do it all at the same time.

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33.612 - 58.337 Madeleine Finlay

She had ordered several intolerance tests. Rebecca pricked her fingers and dripped the blood into tubes, cut off a sample of her hair and sent it all off. Around the world, allergies appear to be on the rise. Some, like hay fever and eczema, are unpleasant and uncomfortable, but ultimately manageable.

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Chapter 2: How common are food intolerances and what are their symptoms?

58.604 - 84.578 Madeleine Finlay

Others have the potential to be deadly. Either way, if you have an allergy, you're likely to know about it. Intolerances also seem to be getting more common, but they're a bit more tricksy. It can be hard to tell exactly what it is that's setting off the stomach aches, bloating and exhaustion. Which is why lots of people turn to intolerance tests like the ones Rebecca was trying out.

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87.545 - 95.073 Madeleine Finlay

When she got her results back, she was faced with some surprisingly long and obscure lists.

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95.894 - 103.762 Rebecca Seal

I'm apparently very sensitive to environmental allergens including bees, European beech, laburnum, primrose, tamarisk and wallflowers.

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105.304 - 112.892 Madeleine Finlay

The thing is, Rebecca wasn't running the experiment to find out what she should avoid. She already knew the answer to that.

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113.272 - 131.429 Rebecca Seal

I don't have any allergies and I don't have any intolerances. No, she was testing the tests themselves. I want to show how ludicrous these tests are and how unfair it is that people are effectively being exploited because they're not cheap in many cases.

Chapter 3: What methods are available for testing food intolerances?

131.589 - 133.853 Rebecca Seal

We're talking hundreds of pounds to buy a test online.

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139.064 - 173.183 Madeleine Finlay

So today, the dangers of intolerance tests. And if there are foods you can't handle, how do you pin them down? From The Guardian, I'm Madeleine Finlay, and this is Science Weekly. Rebecca Seal, you're a food and health writer and your new book is Irritated, the allergy epidemic and what we can do about it. And in it, you also look at intolerances.

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173.223 - 178.656 Madeleine Finlay

So what's the difference between an allergy and an intolerance?

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178.636 - 190.113 Rebecca Seal

So an intolerance effectively is just your body saying, I can't deal with this. I can't digest it. So the primary symptoms are always in the gut or kind of very closely related to the gut.

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Chapter 4: What are the dangers of using at-home intolerance tests?

190.694 - 208.12 Rebecca Seal

Whereas an allergy is an immune system response. So it is a kind of a full body response. Obviously, with some allergies like hay fever, they're in sort of very particular areas of the body. But the impact of an allergy is kind of system wide, whereas an intolerance is really just about how your stomach behaves.

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208.302 - 217.731 Madeleine Finlay

And how common are intolerances? Because we know allergies are on the rise, but what do we actually know about how many people react badly to certain foods?

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218.112 - 238.292 Rebecca Seal

I mean, it's actually really hard to tell because the data collection on allergy isn't particularly brilliant. And it's probably even worse on food intolerances because we don't have kind of really clear definitions of what each intolerance looks like and what the symptoms might be. And we also just have not great data collection on any of this stuff.

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238.492 - 242.759 Madeleine Finlay

And are there particular foods that come up more often than not?

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Chapter 5: What did Rebecca Seal discover from her personal testing experience?

242.779 - 245.904 Madeleine Finlay

Are there foods that people tend to be more intolerant of?

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246.304 - 267.497 Rebecca Seal

So gluten intolerance is obviously a really big one. Lactose intolerance. The difficulty with intolerances for the allergy community... is that because the symptoms aren't necessarily really severe, and sometimes people avoid these products just because they feel a little bit better, they can play a bit fast and loose with their dietary restrictions.

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268.178 - 281.239 Rebecca Seal

And so you get this sort of grey area where sometimes, say, a restaurant doesn't quite understand the difference between an intolerance and an allergy, and that can make it really hard for people with allergies to get taken seriously in some contexts.

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281.219 - 288.948 Rebecca Seal

And that's where there's a little bit of, I would say, beef between the intolerant community and the allergy community, both of whom are having a really rough time.

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292.472 - 311.537 Madeleine Finlay

And like you say, Rebecca, that allergies are often very clear cut. You're going to know what you're allergic to, whereas intolerances, you might be eating lots of different things, not feeling too great, wondering exactly what it is in your diet that is kind of making you allergic. have these horrible gut symptoms.

Chapter 6: How can food intolerance tests lead to dietary restrictions?

312.098 - 324.405 Madeleine Finlay

And so there are tests out there that purport to tell you what your intolerances are. Now, you tried some of these. So tell me about the experience. How do you go about testing for an intolerance?

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324.385 - 346.871 Rebecca Seal

There are a lot of different ways that you can supposedly test for an intolerance. Lactose is the only thing that you can technically test for. That's a hydrogen breath test or a stomach biopsy. So those are big time tests that you do with the doctor. All other intolerance tests do not work. They're not scientifically validated and the data and results that you get after taking them are junk.

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Chapter 7: What is the impact of psychological factors on food intolerance symptoms?

348.072 - 368.433 Rebecca Seal

So there's a full range. You can do IgG blood testing. You can have your hair hair tested. And you can also do things like biomagnetic resonance testing. And there are various ones which are kind of homeopathically based. And even one where you have to hold an allergen or something you're intolerant to in your mouth.

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368.713 - 379.384 Rebecca Seal

And then you have electric currents pass through your body to see what the resistance is to those currents. And if you think that sounds unscientific, that's because it is deeply unscientific.

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379.364 - 384.956 Madeleine Finlay

And knowing this on paper is one thing, but you decided to prove it.

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Chapter 8: How should one properly identify food intolerances without tests?

385.337 - 386.379 Madeleine Finlay

So what did you do?

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386.82 - 394.738 Rebecca Seal

I just ran a bunch of them myself on the same day, which meant I had blood test lancets in the tip of almost every finger that I own.

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396.762 - 421.735 Rebecca Seal

So I did a gold standard allergy test, an ALEX2 test, which tests for 295 different allergens and should only be done with a doctor because it still has a high risk of false positives. And so that's the gold standard. I tested that against a very well-known allergy and intolerance test that I bought online for a couple of hundred quid. And then I did hair testing as well.

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422.437 - 428.575 Rebecca Seal

And in principle, I should have had all of the same results, which is nothing. But that's not what I got.

428.74 - 440.356 Madeleine Finlay

Well, before I ask you what you were intolerant to, just explain these tests, say the blood tests and the hair tests, what do they say that they're actually testing for, looking for?

440.416 - 465.215 Rebecca Seal

So the hair test science is a little vague. They just say that if they take a lock of your hair, they can test it for intolerances. There's not really much information about exactly how that's done. The blood tests do use a lot more scientific language. However, they are testing for something called IgG, immunoglobulin G, which is one of the five classes of antibodies that the body produces.

465.976 - 490.044 Rebecca Seal

It is absolutely unrelated to whether we are intolerant of a food. IgE is a blood test that we do for allergies because immunoglobulin E is what we create in the blood when we have an allergy. And so it's one of the markers that doctors use in order to diagnose an allergy. IgG actually goes up in the bloodstream when we are more tolerant of a food.

490.644 - 496.851 Rebecca Seal

And yet it is what these companies are testing for, which I think shouldn't be allowed.

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