How real (and how common) non-coeliac gluten sensitivity is

The blinded evidence points more to FODMAPs than gluten for many people, but a distinct gluten-driven syndrome in some can’t be ruled out. Genuinely unsettled.

Whether histamine intolerance is a discrete condition

Without a validated biomarker it stays a clinical guess based on response to a low-histamine diet — over-diagnosed, and hard to prove.

Why food-allergy rates have risen

Hygiene, vitamin D, skin barrier and delayed introduction have all been proposed; early introduction clearly helps, but the full cause of the rise is still open.

Digestion, intolerances & allergies, honestly — the difference that matters

The single most useful thing to understand: a food allergy is your immune system overreacting (it can be life-threatening), while an intolerance is your gut struggling to digest something (unpleasant, dose-dependent, not dangerous). Confusing the two — or trusting the wrong test — is where most of the harm and the money go.

Allergy or intolerance?

Allergy or intolerance? — an illustrative chart on this page. Figures use honest, cited or clearly-illustrative data; they are visual aids, not personal measurements.

Allergy or intolerance? Start here

These words get used interchangeably, but medically they are opposites in mechanism. A food ALLERGY is an immune-system reaction: the classic, fast type is IgE-mediated and can cause anaphylaxis — a whole-body emergency treated with adrenaline. A food INTOLERANCE is non-immune — usually a missing enzyme or a gut-chemistry problem — so it is dose-dependent (a little may be fine), builds slowly, and however miserable, it will not kill you.

Coeliac disease is a third thing again: an autoimmune disease, not an allergy and not an intolerance. Getting the category right decides everything downstream — the test, the treatment, and whether a reaction is dangerous.

Early introduction prevents allergy

Early introduction prevents allergy — an illustrative chart on this page. Figures use honest, cited or clearly-illustrative data; they are visual aids, not personal measurements.

What the evidence actually shows

The well-established distinctions worth knowing.

Allergy = immune; intolerance = non-immune — The dividing line is the immune system. IgE-mediated food allergy is reproducible, can be rapid and severe, and is diagnosed by clinical history plus targeted testing. An intolerance (e.g. an enzyme deficiency) is none of those things. (established)
Lactose intolerance is an enzyme deficiency, not an allergy — After weaning, most of the world’s population makes less lactase (the enzyme for milk sugar) — the proportion varies a lot by ancestry. It is dose-dependent, so small amounts are usually fine, and it is confirmed with a hydrogen breath test — not an allergy test. (established)
Coeliac disease must be diagnosed BEFORE going gluten-free — Coeliac is autoimmune: gluten damages the small intestine. It is diagnosed with a blood test (anti-tTG) and, in adults, a biopsy — but only while you are still eating gluten. Cut gluten first and the tests normalise, hiding the disease. Never self-treat suspected coeliac by quitting gluten. (established)
Early allergen introduction PREVENTS allergy — For infants at high risk, introducing peanut early (from 4–11 months) and keeping it up cut peanut allergy at age 5 by around 80% — reversing decades of “avoid it” advice. This is one of the biggest shifts in modern allergy care. (established)

The genuinely useful, with honest limits

Real tools — used correctly.

Low-FODMAP diet for IBS — short-term, dietitian-guided — For irritable bowel syndrome, the low-FODMAP diet has the best evidence of any dietary approach for symptoms — but it is a temporary 3-phase protocol (restrict → reintroduce → personalise), not a lifelong elimination diet. Long-term restriction risks nutrient gaps and harms the gut microbiome; do it with a dietitian. (emerging)
“Gluten sensitivity” is often FODMAP sensitivity — For people without coeliac who feel better off wheat, a blinded trial showed fructans (a FODMAP in wheat), not gluten, reproduced the symptoms in most. Non-coeliac gluten sensitivity is real for some but genuinely contested — and only considered after coeliac and wheat allergy are ruled out. (note)
Histamine intolerance — plausible but poorly defined — A proposed reaction to histamine-rich foods (aged cheese, wine, cured meat) from low DAO enzyme activity. It is plausible, but there is no reliable test, it is frequently over-diagnosed, and commercial “DAO deficiency” tests and supplements run well ahead of the evidence. (note)

What’s oversold — and can be dangerous

IgG “food sensitivity” blood tests — A positive food-IgG simply means you eat and tolerate that food — it is a marker of exposure, not intolerance. Allergy societies advise against these tests: they generate long, needless elimination diets, and are dangerous if they mask a real IgE allergy. Same verdict for hair-analysis and “applied kinesiology” intolerance tests: no diagnostic validity. (hype)
Broad IgE test “panels” without symptoms — Testing dozens of foods in someone with no matching history throws up false positives and needless avoidance. Real allergy diagnosis starts from the clinical story, then targets the test — ideally an oral food challenge. (hype)

What we still don’t know

How real (and how common) non-coeliac gluten sensitivity is The blinded evidence points more to FODMAPs than gluten for many people, but a distinct gluten-driven syndrome in some can’t be ruled out. Genuinely unsettled.
Whether histamine intolerance is a discrete condition Without a validated biomarker it stays a clinical guess based on response to a low-histamine diet — over-diagnosed, and hard to prove.
Why food-allergy rates have risen Hygiene, vitamin D, skin barrier and delayed introduction have all been proposed; early introduction clearly helps, but the full cause of the rise is still open.

Red flags — see a doctor, not a diet

Some digestive symptoms should never be self-managed as “an intolerance”: unintentional weight loss, blood in the stool or rectal bleeding, iron-deficiency anaemia, difficulty swallowing, a lump in the abdomen, or a new persistent change in bowel habit — especially over about 50. These alarm features can signal cancer, inflammatory bowel disease or coeliac disease, and warrant prompt medical assessment, not an elimination diet.

Key terms

Allergy An immune-system reaction to a food; the fast IgE type can be severe or life-threatening (anaphylaxis).
Intolerance A non-immune reaction, often a missing enzyme; usually dose-dependent and unpleasant but not dangerous.
IgE The antibody behind true, fast allergic reactions — the basis of allergy testing, used together with the clinical history.
IgG An antibody that mostly signals you’ve eaten and tolerate a food; NOT a valid marker of intolerance, despite being sold as one.
Anaphylaxis A severe, rapid, whole-body allergic reaction affecting breathing and circulation; a medical emergency treated with adrenaline.
Coeliac disease An autoimmune disease where gluten damages the small intestine; diagnosed by blood test + biopsy while still eating gluten.
FODMAPs Fermentable carbs (in wheat, onion, some dairy and fruit) that can trigger gas, bloating and IBS symptoms.
Lactase The gut enzyme that digests lactose (milk sugar); low levels cause lactose intolerance.
DAO Diamine oxidase, the enzyme that breaks down histamine; low activity is the proposed (unproven) basis of histamine intolerance.