Science Weekly: The Dangers of Intolerance Tests and How to Pin Down Food Reactions

The podcast investigates intolerance tests for foods, explaining the difference between allergies and intolerances and exposing how some tests sold online can mislead consumers. Rebecca Seal recounts her self-experiment comparing a gold standard allergy test with online tests and a hair test, showing contradictory results and the potential harm of misinterpretation. The discussion also covers nocebo effects, data quality in allergy research, and practical steps for anyone trying to diagnose food-related symptoms.

• Differentiate between food allergies and intolerances and why it matters for treatment.
• Online intolerance tests often produce junk data and can mislead, especially for children.
• Nocebo effects can amplify gut symptoms even when foods are not truly problematic.
• Exclusion diets, reintroduction, and professional guidance are the recommended path to identify triggers.

Definitions and the allure of food as medicine

The podcast begins by drawing a sharp distinction between food allergies, which involve an immune system response, and intolerances, which primarily affect the gut and digestion. Rebecca Seal explains that while allergies can be life-threatening, intolerances tend to cause gut-related symptoms that are not always clear-cut. The host and guest discuss how this distinction matters for everyday life, including the way restaurants and policies treat people with allergies versus intolerances.

"An intolerance, effectively, is just your body saying, I can't deal with this, I can't digest it." - Rebecca Seal

The data problem in allergy and intolerance research

The conversation moves to data quality, noting that allergy data collection is not great and that there is even less clarity around defining and diagnosing food intolerances. This lack of clear definitions complicates both clinical practice and consumer testing, making it hard to pin down which foods cause symptoms for whom.

"it's actually really hard to tell because the data collection on allergy isn't particularly brilliant." - Rebecca Seal

The testing landscape and what the tests actually measure

The discussion then turns to the spectrum of intolerance tests available, highlighting that lactase (lactose intolerance) can be tested via hydrogen breath tests or biopsy, but many other at-home tests lack scientific validation. Rebecca emphasizes that some tests measure immunoglobulin G (IgG), a marker that rises with tolerance to foods, not with intolerance, which is exactly opposite of what some commercial tests claim to reveal. This leads to confusion and potential dietary restrictions based on misleading data.

"IgG actually goes up in the bloodstream when we are more tolerant of a food. And yet it is what these companies are testing for" - Rebecca Seal

Rebecca Seal's experiment: what she did and what the results showed

In a hands-on experiment, Seal ran several tests on the same day, including a gold-standard ALEX 2 test and an online intolerance test. She also used a hair-test and contrasted results from the tests. The outcome was strikingly inconsistent: the gold-standard test and IgG-based tests produced conflicting guidance, and the hair test suggested unusual restrictions that did not align with any real intolerance. The seven allergy results were normal, but the IgG results suggested avoiding various items, many of which Seal had actually eaten recently during a celebratory meal, illustrating how IgG testing can reflect recent exposure rather than true intolerance.

"The hair test told me I needed to minimise my consumption of high reactivity items as much as possible" - Rebecca Seal

Risks and consequences of relying on home tests

The episode highlights the dangerous downstream effects of misinterpreting test results. There is a risk of disordered eating, including orthorexia and avoidant/restrictive food intake disorders, particularly in children who might be kept away from common allergens without medical supervision. Seal stresses that early introduction of potentially allergenic foods, especially for infants at risk, is critical to developing tolerance and preventing real allergies, so erroneous results could increase risk rather than reduce it.

"The two damaging things that these results can create is disordered eating... and it can contribute to the development of a true IgE allergy" - Rebecca Seal

What should people do if they suspect an intolerance

Rather than turning to at-home tests, the podcast advocates an exclusion diet followed by careful reintroduction to identify true triggers, ideally under the guidance of a dietitian or gastroenterologist. The discussion cautions that home tests can create a false sense of diagnosis, potentially delaying appropriate treatment for other conditions and leading to unnecessary restrictions.

"The only way to work out whether you have an intolerance is to do an exclusion diet and then reintroduce the food" - Rebecca Seal

Why tolerance testing is so appealing and how to move forward

The episode closes by examining the cultural moment driving interest in dietary tests: the notion that food is medicine, the desire for a personalized health solution, and gaps in healthcare around nutrition, allergies, and intolerances. Seal emphasizes that science-based guidance—plus access to competent care—remains essential to avoid the harms of popular but scientifically unfounded tests. The takeaway is clear: if you think you have an intolerance, seek professional evaluation and use exclusion and reintroduction as a robust strategy to determine what, if anything, to avoid.

"The only way to work out whether you have an intolerance is to do an exclusion diet... But it's really crucial to know whether that trigger food really is creating symptoms in your body" - Rebecca Seal