Glossary
Food Intolerance
Updated February 28, 2026
Food intolerance is a dose-dependent digestive response caused by enzymatic deficiency, transport limitation, or chemical sensitivity. It is mechanistically distinct from food allergy, which involves IgE-mediated immune activation with rapid, potentially systemic consequences. Confusing the two leads to either unnecessary dietary restriction or dangerous underreaction.
Mechanism comparison
| Condition | Mechanism | Onset | Practical signal |
|---|---|---|---|
| Intolerance | Enzymatic or transport deficiency (e.g., lactase, fructose carrier) | Hours (typically 2 to 12) | Dose-related GI symptoms: bloating, gas, cramping, diarrhea |
| Sensitivity | Non-IgE immune or chemical response (e.g., gluten, histamine, sulfites) | Hours to days | GI symptoms plus potential headaches, fatigue, skin reactions |
| Allergy | IgE-mediated immune activation | Minutes to 2 hours | Hives, swelling, breathing difficulty, anaphylaxis in severe cases |
Lactase deficiency is the most common food intolerance globally, affecting roughly 65 to 70% of the world's adult population. Most people with lactase deficiency can tolerate small amounts of dairy (particularly fermented forms like yogurt and aged cheese) because the dose determines the symptom, which is the defining characteristic of intolerance versus allergy.
Elimination and reintroduction protocol
A structured elimination protocol is the primary diagnostic tool for food intolerance. The goal is to reduce symptom noise, then reintroduce suspected triggers one at a time to identify thresholds.
| Phase | Duration | Action |
|---|---|---|
| Full elimination | 2 to 4 weeks | Remove all suspected food classes completely. 10 to 14 days is often too short for intolerances with delayed or cumulative symptom patterns |
| Reintroduction | 3 days per food group | Reintroduce one food group at a time. Start at a small dose on day 1, increase to a normal portion on day 2, and monitor through day 3 before moving to the next group |
| Journaling | Continuous | Log the food, the dose, the timing, and any symptoms with severity rating (0 to 10). Track GI symptoms, energy, skin, and sleep quality |
For IBS-pattern symptoms (alternating constipation and diarrhea, bloating after meals with no clear single trigger), the low FODMAP diet developed at Monash University is the most evidence-supported elimination framework. It removes fermentable oligosaccharides, disaccharides, monosaccharides, and polyols in a structured sequence. FODMAP elimination should be supervised by a dietitian because long-term restriction can reduce beneficial gut bacteria diversity and narrow the gut microbiome.
Escalation criteria
| Trigger | What to do |
|---|---|
| Persistent symptoms after a full elimination cycle | Seek clinician-guided testing (hydrogen breath test for lactose or fructose, celiac serology for gluten) |
| Severe systemic signs (breathing difficulty, swelling, rapid heart rate) | Urgent care pathway. These suggest allergy, not intolerance |
| Repeated severe GI reactions across multiple food groups | Evaluate with a gastroenterologist or dietitian for broader conditions (SIBO, IBD, mast cell activation) |
| Weight loss, nutrient deficiency, or prolonged restriction | Dietitian review to ensure the elimination diet itself is nutritionally adequate |
Use lactose intolerance and food allergy tracking for deeper coverage of specific conditions.