An honest comparison of three routes: the elimination diet (the most reliable), blood IgG tests (quick but debated) and hair screening (an accessible starting point). No method tells you your intolerances on its own — what settles it is changing what you eat and watching how you feel.
Food intolerance is different from a food allergy. A true food allergy triggers an immediate immune response (IgE antibodies) and can cause serious, sometimes dangerous symptoms. Food intolerances tend to be delayed or dose-dependent, with discomfort building over hours or even a day or two.
These reactions are thought to happen when the body finds certain foods harder to handle, or responds to naturally occurring compounds within them. Symptoms such as bloating, stomach discomfort, low energy or skin changes can feel random, yet they often follow a pattern once you start paying attention. The tricky part is that reactions are highly individual: a food that bothers your friend may not affect you at all. That is exactly why observing your own body’s response, rather than leaning on generic food lists, is so useful.
Before you explore intolerance at all, though, please see your GP first. Several conditions — coeliac disease, inflammatory bowel disease, thyroid problems, anaemia and infections among them — can produce very similar symptoms, and they need proper medical assessment, not a food experiment. Only once your GP has ruled those out does it make sense to start exploring which foods might be affecting you.
The Most Reliable Route: Elimination Diet and Food Diary
An elimination diet, paired with a food and symptom diary, is the most reliable way to work out which foods affect you. Here is how it works. You remove a small number of suspected foods for six weeks, writing down everything you eat and how you feel each day — start the diary on day one. Once symptoms have settled, you reintroduce foods one at a time, leaving three to five days between each so any delayed reaction has time to show itself.
This approach has the strongest supporting evidence and is the method NHS dietitians and allergy specialists generally favour. The reason is simple: it lets your own body give you the answer, food by food, rather than relying on a list someone else drew up. It costs nothing beyond the food itself, and the picture you build is personal to you.
Now the honest drawbacks. It asks for real discipline — you will be reading labels, planning meals and resisting the odd temptation for weeks. Your records have to be accurate, because if you cannot remember what you ate, the patterns disappear. Some people find restricting foods genuinely hard going, especially at the start, and it is slow. It is also not completely watertight: if you change several things at once — less alcohol, more sleep, less stress — it can be hard to know which change made the difference, and expecting to feel better can colour how you judge things.
Even so, when you work through it carefully, you usually end up with a far clearer sense of your own thresholds, and many people are reassured to find they tolerate more foods than they feared.
Blood IgG Testing: What the Research Actually Says
IgG blood tests look for antibodies your immune system makes in response to specific foods, and you typically get a list of results within one to two weeks. Here is the honest position. The research is contested. All of us — whether a food bothers us or not — produce IgG antibodies when we eat. IgG is simply a sign that your immune system has met a food protein. It can reflect exposure, tolerance or sensitivity, and right now there is no dependable way to tell which from the reading alone.
Major bodies, including the American Academy of Allergy, Asthma and Immunology and McGill University’s Office for Science and Society, stress that the presence of IgG does not equal intolerance. Plenty of people show high IgG to foods they eat happily every day. Studies have also found that the same person’s results can differ when they are tested twice, which raises real questions about reliability.
Some people do say they feel better after cutting out their high-IgG foods — but the most likely explanation is the process of carefully removing and reintroducing foods (and watching the results), or simple expectation, rather than the antibody reading itself. Costs typically fall in the £130–£240 range. The NHS does not generally offer IgG testing for food intolerance, because the evidence supporting it is weak.
Hair Screening: A Non-Invasive Starting Point
Hair screening offers an accessible, non-invasive way to produce a shortlist of foods worth exploring through elimination. All it needs is 9 or 10 strands of hair — no needles and no fuss. IntoleranceLab’s Gold screening costs £49, returns results within 3 working days of your sample reaching the UK lab, and comes with a 90-day money-back guarantee. For the price and convenience, many people find it a practical place to begin.
But let us be completely straight about it. Hair screening has no peer-reviewed research supporting its accuracy. The lab uses its own proprietary screening method, and this category of hair screening has not been validated by independent studies. UK and US regulators (the MHRA and FDA) have not approved hair screening as a medical test for food intolerance. And unlike blood, which carries circulating antibodies when the immune system reacts, a strand of hair holds no measurable immune markers.
So treat a hair result as a conversation starter, never as a verdict. Its real value only appears when you take the shortlist and put it to the test through elimination. If your hair screening flags dairy, you then remove dairy, keep your diary, and watch what actually happens over the six weeks — and any change you notice comes from that elimination-and-reintroduction process, not from the screening result. Used this way — screen to narrow the field, then confirm through elimination — it pairs affordability and convenience with the more reliable answer that only changing your diet can give. It is most helpful when the list of possible culprits feels overwhelming and you want a sensible place to start.
And here is the part it has over the other two routes: it is non-invasive with no blood draw, the most affordable of the three at £49, turns your report around within 3 working days of your sample reaching the lab, and it is the only one carrying a 90-day money-back guarantee — so if the six-week elimination plan it points you to leaves you no better, you are not out of pocket.
Which Route Is Right for You?
Start with your GP — every time. Conditions such as coeliac disease, lactose intolerance, thyroid problems and infections need to be ruled out first, and your GP can arrange those checks on the NHS. Once serious causes are off the table, your choice comes down to your priorities.
If you have the time and patience and want the clearest answer, begin the elimination diet now: a six-week core elimination phase plus a few weeks of careful reintroduction usually gives you a solid picture within eight to ten weeks. If you would like a quick sense of possibilities but cannot face full elimination yet, a blood IgG test might appeal — just hold its results loosely, as questions rather than answers. If cost and convenience matter most, or you simply want to shrink a long list of suspect foods, try hair screening such as IntoleranceLab’s, then put whatever it flags through a focused elimination. You can also combine routes: screen first to narrow the field, then run your six-week elimination on just those foods. (One practical note if you use our screen: the 90-day money-back guarantee asks you to follow your plan for at least 6 weeks with a food diary — so start your diary on day one.)
Whichever you pick, keep one thing front of mind — no test can confirm a food intolerance by itself. What settles it is how your body actually responds when you remove a food and bring it back. The test only points you somewhere to look; the answer comes from what you eat and how you feel afterwards.
Making Sense of Your Results and Next Steps
Whatever method you use, read the results as a working hypothesis rather than a final word. If your elimination diet points clearly to a food, that is the most trustworthy signal you will get. If a blood test shows high IgG to something you eat with no trouble, you can set it aside — IgG on its own does not tell you a food is a problem. If a hair result flags a food you feel perfectly fine eating, you are under no obligation to give it up. The aim is to explore thoughtfully, not to end up frightened of your own dinner.
As you remove foods, keep detailed notes: what you ate, when, and how you felt across energy, digestion, skin and mood. Patterns often only become visible when you look back over a week of entries. When you reintroduce foods, go slowly and one at a time — some reactions appear within hours, others take two or three days, so patience during reintroduction really matters. Any improvement you notice comes from this process of changing what you eat and observing the result, not from any test reading.
If the whole thing feels complicated — several suspected foods, or worries about getting enough nutrients — consider working with a registered dietitian, who can help you keep your diet balanced and enjoyable while you explore. Remember too that intolerances can shift over time, influenced by gut health, stress and life in general; what bothers you now may not in six months, and the reverse is true too. Stay flexible and curious. And if your symptoms persist, get worse, or you notice anything worrying such as unintentional weight loss or blood, stop and go back to your GP.
If, after weighing the three routes, a focused shortlist feels like the right first step, ours costs £49 and is backed by the 90-day money-back guarantee — the honest condition being that you actually run the six-week plan with a food diary. If you do and you’re no better, you get your money back.
At a glance
Cost
Timeline
Strengths
Honest Limits
Elimination Diet + Food Diary
Free (ingredients only),Roughly 8–10 weeks: a six-week core elimination, then reintroduction one food at a time,Strongest evidence; favoured by NHS dietitians. Personal to your own body. Costs nothing.,Needs discipline and accurate records. Slow. Food restriction can be hard going.
Blood IgG Tests
£130–£240 typically,Results in 1–2 weeks,Quick. Measures a real antibody. No exclusion phase needed.,IgG reflects exposure, not intolerance. Results can differ on repeat testing. Not offered by the NHS.
Hair Screening (IntoleranceLab Gold)
£49,Results within 3 working days of the sample reaching the lab,Non-invasive, affordable shortlist-maker. 90-day money-back guarantee. Handy for narrowing a long list.,No peer-reviewed evidence; proprietary method. A starting point only — confirmation comes from elimination.
Low FODMAP Elimination (Simplified Alternative)
Free,4–8 weeks,Good evidence for digestive symptoms. Teaches you which carbohydrates suit you.,Only for digestive symptoms. Misses protein and additive sensitivities. Works best with dietitian support.
Being straight with you
A non-invasive screening tool that generates a personalised shortlist of foods worth exploring through elimination
An affordable way to get a starting point when you have many possible culprits
Designed to be used before or alongside an elimination diet, not in place of one
Backed by our 90-day money-back guarantee — conditions disclosed plainly: follow the 6-week elimination plan and keep a simple food diary
Practical for people who want to narrow the field before committing to full elimination
A medical test, and not approved as one by regulatory bodies (MHRA, FDA)
Supported by peer-reviewed research as an accurate method
A replacement for an elimination diet — only elimination can confirm which foods actually affect you
Suitable on its own for anyone with a true food allergy (IgE-mediated reactions with serious symptoms)
A substitute for seeing your GP if you have serious or persistent symptoms
Common questions
Can a hair screening tell me my food intolerances on its own?
No. No test can confirm a food intolerance by itself. Hair screening gives you a shortlist to explore, but the only way to know whether a food actually affects you is to remove it, see how you feel, then reintroduce it and watch what happens. That elimination-and-reintroduction process is the most reliable route there is.
Is hair screening better than IgG blood tests?
They are simply different. Hair screening is non-invasive and affordable but has no scientific backing. IgG blood tests measure a real antibody, but its presence does not reliably tell you a food is a problem. Both are starting points only, and an elimination diet is more reliable than either.
How long does an elimination diet take?
Allow roughly eight to ten weeks for the full picture: a six-week core elimination phase with a food diary, then several weeks reintroducing foods one at a time, leaving three to five days between each. Patience matters, because some reactions take two or three days to appear. It is slower than a test, but it gives you a much clearer picture of your own body — and if you’re using our screen, the 90-day money-back guarantee asks you to follow your plan for at least 6 weeks with a food diary, so start your diary on day one.
Should I see my GP before I start?
Yes, absolutely. Your GP should first rule out coeliac disease, lactose intolerance, thyroid problems, anaemia, infections and other conditions that can mimic food intolerance. Only once those have been excluded does it make sense to explore intolerance through screening or an elimination diet.
Could my symptoms be caused by something else?
Yes. Symptoms like bloating, fatigue or stomach pain can point to a range of conditions, from coeliac disease and inflammatory bowel disease to thyroid problems, anaemia, infections or anxiety. That is exactly why seeing your GP first is so important — they can run simple checks to rule these out before you start changing your diet.
When to speak to your GP. IMPORTANT: See your GP first. Food intolerance symptoms — bloating, stomach pain, fatigue, skin changes — overlap with serious conditions including coeliac disease, inflammatory bowel disease (Crohn’s, ulcerative colitis), thyroid disorders, anaemia and infections. Your GP can arrange NHS checks to rule these out. Only once serious causes have been excluded should you explore intolerance through screening or an elimination diet. If your symptoms persist, get worse, or you lose weight without meaning to, go back to your GP. Food intolerance screening (hair, blood or elimination diet) is not a substitute for medical care.
