Food Sensitivity and Brain Fog
Guideline: NICE Food Allergy in Children and Young People; Clinical practice consensus
What Is Food Sensitivity-Related Brain Fog?
The fog you can't trace. Unlike true allergies (anaphylaxis), food sensitivities cause delayed reactions — 24-72 hours after eating. You blame stress when it was the food you ate yesterday or the day before. Identifying trigger foods requires systematic elimination and reintroduction.
What to Do This Week
Seven actionable steps you can start today — free, evidence-based, and designed for when you're foggy.
Body
Note any physical symptoms alongside cognitive symptoms.
Food
Start a detailed food diary today. Record everything eaten and all symptoms with timing.
Water
Standard hydration.
Environment
Prepare for elimination phase: meal plan, stock safe foods.
Connection
Tell household members you're doing an elimination trial — their support helps.
Tracking
Detailed diary is essential. Apps like Cara, Fig, or simple notebook work.
Avoid
Don't buy IgG sensitivity tests. Don't eliminate randomly. Don't stay on restrictive diet forever.
What to Eat: The Elimination-Reintroduction Protocol Approach
Systematic removal and reintroduction to identify YOUR triggers.
Sample Day
- breakfast: 2 eggs scrambled in olive oil + handful spinach + slice sourdough + blueberries
- lunch: Big salad (mixed greens, chickpeas, cucumber, tomato, feta, olive oil + lemon) + water
- snack: Apple + handful walnuts or almonds
- dinner: Salmon or chicken thigh + roasted vegetables (broccoli, sweet potato, red onion) + olive oil
- evening: Herbal tea (chamomile or peppermint)
For Food Sensitivity: Everyone's triggers are different. Commercial sensitivity tests are not reliable. The elimination-reintroduction process identifies YOUR specific triggers.
This is a PATTERN, not a prescription. Adapt to your budget, culture, preferences, and what's available. The principles matter more than perfection: more plants, good fats, less processed food.
When to Seek Urgent Help
STOP — Seek immediate medical care if: difficulty breathing, throat swelling, severe reaction after eating. These suggest true allergy (anaphylaxis), not sensitivity. Sensitivities don't cause anaphylaxis.
Tests and Investigations
Consider Medical Testing for Specific Conditions
- Celiac panel (tTG-IgA) — rules out celiac disease
- Lactose intolerance breath test
- IgE food allergy testing (for true allergies, not sensitivities)
Note: IgG food sensitivity panels are NOT recommended — they show exposure, not sensitivity. Elimination diet is more reliable than commercial sensitivity tests.
Evidence-Based Lifestyle Changes
Food-Symptom Diary
For 2 weeks: record everything eaten, all symptoms (type, timing, severity). Use an app or notebook. Review for patterns.
Evidence: Clinical consensus — essential first step
Elimination Diet
Remove suspected trigger foods for 2-4 weeks. Common triggers: gluten, dairy, eggs, soy, corn, nuts, nightshades. Then systematically reintroduce one food every 3-4 days.
Evidence: Moderate — elimination-reintroduction is the gold standard for identifying food sensitivities
Gut Healing (if gut involvement)
If gut symptoms accompany sensitivity: address underlying gut health. See Gut (#09) entry.
Evidence: Moderate
Holistic Support
Systematic elimination-reintroduction
Moderate — the most reliable method
Work with a dietitian. Eliminate common triggers 2-4 weeks. Reintroduce one at a time.
Gut health support
Moderate — underlying gut issues may cause sensitivities
See Gut entry. Address dysbiosis, leaky gut, SIBO if present.
Medical Treatment Options
Discuss these options with your prescribing physician. This information is educational, not medical advice.
Dietitian Support
Work with a dietitian experienced in food sensitivities for safe elimination and reintroduction.
Evidence: Clinical consensus
Rule Out True Allergy
If reactions are severe or immediate, see an allergist to rule out IgE-mediated allergy.
Evidence: Standard of care
Supplements — What the Evidence Says
Supplements are adjuncts, not replacements for lifestyle changes. Discuss with your healthcare provider.
Digestive enzymes (optional)
Dose: As directed on product
May help with digestion of trigger foods when unavoidable. Not a substitute for avoidance.
Psychological Support and Therapy
Dietitian specializing in food sensitivities. Allergist to rule out true allergy. If food-related anxiety develops, consider therapy support.
What People With Food Sensitivity Brain Fog Say
What Helped
- • Elimination diet with careful reintroduction — finally identified my triggers
- • Food diary — saw patterns I hadn't noticed
- • Realizing reactions are delayed 24-72 hours — stopped blaming 'stress'
- • Working with a dietitian — made elimination safe and systematic
What Didn't Help
- • Commercial IgG sensitivity tests — expensive and unreliable
- • Eliminating everything at once without plan for reintroduction
- • Assuming sensitivities are permanent — many resolve with gut healing
Common Mistakes
- • Wasting money on IgG sensitivity tests (not evidence-based)
- • Eliminating forever without trying reintroduction after gut healing
- • Not being systematic — random elimination doesn't work
Surprises
- • How delayed the reactions are — 24-72 hours makes it hard to connect
- • That gut healing reduced sensitivities over time
- • Common foods I ate every day were the culprits
"Food sensitivities cause delayed reactions (24-72 hours) — that's why they're hard to identify. Don't waste money on IgG tests. Do a systematic elimination diet with careful reintroduction. Keep a detailed food-symptom diary. Many sensitivities improve when gut health improves."
Quick Reference
Quick Win
Start a food-symptom diary for 2 weeks. Record everything you eat and all symptoms (including timing). Look for patterns. Then try a 2-4 week elimination of suspected foods, followed by systematic reintroduction.
Turnbull et al., JACI Practice — Food intolerance