“I’m allergic to [insert food].” — said by 1 in 5 adults. Actual food allergies confirmed by oral challenge — closer to 1 in 25. Most of what people call “food allergies” are actually food intolerances or IBS.

The difference matters because the implications are wildly different: an allergy can kill you; an intolerance is uncomfortable but not dangerous; IBS is hypersensitivity without any specific food as the root cause. Here’s how to tell them apart.

The three mechanisms in one paragraph each

Food allergy is an immune system attack on a specific protein in a specific food. The body mistakes a harmless food protein for a parasite or pathogen and mounts a defense — histamine release, swelling, sometimes anaphylaxis. The dose threshold is tiny (crumbs can do it) and reactions are fast (minutes to 2 hours). Common in childhood, less common but possible in adults. Tested by skin prick, IgE blood test, or supervised oral food challenge.

Food intolerance is a non-immune reaction. The mechanism varies: missing enzymes (lactose intolerance), drug-like effects of food chemicals (histamine, tyramine, caffeine, MSG, sulfites), pharmacological reactions (gluten in non-celiac sensitivity), or fermentation effects (FODMAPs). Reactions are dose-dependent (a little is fine, a lot is not) and slower (30 minutes to a day later). Not life-threatening. No reliable blood test exists for most intolerances — diagnosis is by elimination diet.

IBS is hypersensitivity of the gut’s nervous system. The same volume of normal gut gas that wouldn’t bother anyone else fires pain signals to your brain. IBS often has food triggers (FODMAPs, fatty foods, caffeine, alcohol), but the food isn’t the underlying disease — the sensitivity is. Treatment is gut-directed (low-FODMAP, stress management, sometimes medication) rather than “avoid this one food forever.”

A quick “which one is it” decision tree

Start with your symptom pattern.

Do reactions involve skin, lips, throat, or breathing? → Yes: this is allergy until proven otherwise. See an allergist. Carry an epinephrine auto-injector. Don’t run home experiments. → No: keep going.

Is the reaction “all or nothing” (crumb-sized exposure triggers it)? → Yes: likely allergy or celiac disease. → No: dose-dependent → intolerance or IBS.

Is there one specific food that’s always the culprit, even when eaten alone? → Yes: likely intolerance (e.g., a specific enzyme deficiency or food chemical reaction). → No: triggers are inconsistent or cluster around “lots of fermentable carbs” → IBS-style.

Do symptoms include bloating, urgency, and pain that resolves with bowel movement, plus a pattern of being worse during stress? → Yes: this is the IBS signature, regardless of whether food triggers it.

Many people have two or three at once. A common cluster in adults: celiac disease + lactose intolerance + IBS. The labs and elimination diets sort out which contributes what.

The “they look the same” trap

Bloating and stomach pain are the least specific symptoms in medicine. They can mean:

  • Food intolerance (any of dozens of mechanisms)
  • IBS (in any of its three subtypes)
  • Celiac disease (autoimmune attack on gluten)
  • IBD (Crohn’s, ulcerative colitis)
  • Gastroparesis (slow stomach emptying)
  • SIBO (bacterial overgrowth)
  • Pelvic floor dysfunction
  • Endometriosis (in women — often misdiagnosed as IBS for years)
  • Less commonly: ovarian, pancreatic, colorectal cancers

That’s why an actual workup matters. If you’ve been told “it’s just IBS” and you have any red flags — blood in stool, unintended weight loss, fever, night-waking symptoms, abnormal blood work, family history of IBD or colon cancer, or symptoms that started after age 50 — push for more investigation.

Why “food allergy testing” panels are mostly garbage

The wellness industry sells IgG food sensitivity panels promising to identify your trigger foods. Major allergy organizations have publicly stated these tests are not clinically valid. A positive IgG result means your immune system has seen that food — which is normal for any food you eat regularly. It doesn’t predict symptoms.

What IS validated:

  • IgE testing for true allergies (skin prick or blood)
  • Tissue transglutaminase IgA for celiac disease (must be eating gluten when tested)
  • Hydrogen/methane breath tests for lactose, fructose, or SIBO
  • Calprotectin stool test to screen IBS vs IBD
  • Supervised elimination + reintroduction for food intolerances and IBS — still the gold standard

What’s NOT validated:

  • IgG food panels
  • “Hair analysis” allergy tests
  • Applied kinesiology / muscle testing
  • ALCAT, MRT, LEAP tests
  • Most direct-to-consumer “food sensitivity” tests sold by wellness brands

If a clinic offers you a 100-food panel with no medical workup, walk out.

What to do this week, in order of value

  1. List your symptoms honestly. Gut-only or systemic (skin, breathing)? Always after specific foods, or random?
  2. If you have any allergy-style symptoms, get an allergist appointment before anything else.
  3. Get celiac screening. A blood test (TTG-IgA). It must be done while still eating gluten — going gluten-free first will give false negatives. Celiac is autoimmune, not an intolerance, and missing it has long-term consequences.
  4. Calprotectin stool test if your doctor hasn’t ordered one — it’s cheap and rules out IBD.
  5. Once allergy and serious disease are excluded, treat your symptoms as IBS + possible specific intolerances. Run a structured low-FODMAP elimination, then reintroduce by family.
  6. Keep a symptom diary. Not a food diary alone — log food + symptom + stress + sleep + cycle (if applicable). Patterns only emerge when you have all four columns.

Bottom line

“I think I’m allergic to gluten” — for the vast majority of adults, the real answer is not allergy, sometimes celiac disease, often IBS triggered by FODMAPs in wheat. The differential matters because:

  • A real allergy means strict avoidance forever and emergency preparedness
  • Celiac means strict gluten avoidance forever, plus screening relatives
  • An intolerance means dose-management — you can still eat the food in smaller amounts
  • IBS means it’s not really about that one food — it’s about your gut’s overall sensitivity

The pathway you take depends on which one (or which combination) is real. Don’t take the lazy answer.