Food Intolerance
Non-immune mediated food reactions and differential diagnosis.
Overview
Food intolerance is a non-immune mediated adverse reaction to food that does not involve the immune system. Unlike food allergies, food intolerances are typically dose-dependent and do not cause life-threatening reactions. Common examples include lactose intolerance, fructose malabsorption, and reactions to food additives.
difference
allergy
Immune-mediated, can be life-threatening, small amounts trigger reactions, involves IgE or other immune mechanisms
intolerance
Non-immune mediated, not life-threatening, typically dose-dependent, involves digestive enzymes, absorption, or other non-immune mechanisms
types
enzymatic
name
Enzyme Deficiencies
examples
- Lactose intolerance - deficiency of lactase enzyme
- Fructose malabsorption - deficiency of GLUT5 transporter
- Histamine intolerance - deficiency of DAO enzyme
mechanism
Inability to properly digest or metabolize specific food components
pharmacological
name
Pharmacological Reactions
examples
- Caffeine sensitivity
- Tyramine in aged cheeses (can trigger migraines)
- Salicylates in various foods
mechanism
Reaction to naturally occurring chemicals in foods
additive
name
Food Additive Reactions
examples
- Sulfites (preservatives in wine, dried fruits)
- MSG (monosodium glutamate)
- Artificial colors and flavors
- Nitrates/nitrites
mechanism
Reaction to added chemicals in processed foods
functional
name
Functional GI Disorders
examples
- Irritable bowel syndrome (IBS) triggered by FODMAPs
- Non-celiac gluten sensitivity
- Functional dyspepsia
mechanism
Food triggers symptoms in sensitive individuals without clear structural or biochemical abnormality
symptoms
gastrointestinal
- Bloating
- Abdominal pain or cramping
- Diarrhea
- Constipation
- Nausea
- Gas
- Indigestion
other
- Headaches or migraines
- Fatigue
- Brain fog
- Joint pain
- Skin rashes (less common)
- Mood changes
timing
Symptoms typically appear hours to days after ingestion, making identification of triggers challenging
common Triggers
lactose
Dairy products - milk, cheese, yogurt, ice cream
fructose
Fruits, honey, high-fructose corn syrup
gluten
Wheat, barley, rye (in non-celiac gluten sensitivity)
histamine
Aged cheeses, fermented foods, wine, processed meats
fodmaps
Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols - found in many fruits, vegetables, and grains
additives
Sulfites, MSG, artificial colors, preservatives
evaluation
history
- Detailed symptom diary - timing, frequency, severity
- Food diary - everything consumed with symptoms
- Family history of intolerances
- Onset and progression of symptoms
- Dose-response relationship
- Pattern of symptoms (consistent vs variable)
physical
General physical exam focusing on GI symptoms, nutritional status
testing
lactose
- Lactose breath test (hydrogen breath test)
- Lactose tolerance test
- Genetic testing for lactase persistence
fructose
Fructose breath test
elimination
Elimination diet followed by gradual reintroduction to identify triggers
note
No reliable blood tests for most food intolerances (unlike food allergies)
differential
- Food allergy (IgE or non-IgE mediated)
- Celiac disease
- Inflammatory bowel disease
- Functional GI disorders
- Other GI conditions
management
dietary
- Identify and avoid trigger foods
- Low FODMAP diet for IBS (under guidance)
- Lactose-free diet for lactose intolerance
- Histamine-restricted diet for histamine intolerance
- Gradual reintroduction to determine tolerance thresholds
enzyme
- Lactase supplements for lactose intolerance
- Take with first bite of dairy-containing foods
- Available over-the-counter
symptom
- Antacids for indigestion
- Antispasmodics for cramping
- Probiotics (evidence mixed)
- Fiber supplements for constipation
education
- Reading food labels carefully
- Understanding hidden sources of triggers
- Meal planning and preparation
- Eating out strategies
when To Refer
- Unclear diagnosis after initial evaluation
- Severe or persistent symptoms
- Nutritional concerns or weight loss
- Need for specialized testing (breath tests, etc.)
- Complex elimination diets requiring dietitian support
- Suspicion of food allergy rather than intolerance
prognosis
Food intolerances are typically manageable with dietary modifications. Most patients can identify their triggers and learn to avoid or limit problematic foods. Some intolerances may improve over time, while others require lifelong dietary management. Quality of life can be significantly improved with proper identification and management of triggers.
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