Quick answer: A food diary for food intolerance should record three things most diaries skip: the ingredients in each dish (including sauces, dressings and drinks), the time you ate and the time symptoms started, and roughly how much you had. Intolerance symptoms often appear hours later and depend on the dose, so "had pasta, felt bloated" isn't enough. Keep it for 2–4 weeks before drawing conclusions.
Food intolerance is slippery. The same yogurt is fine on Monday and a problem on Thursday. A meal you've eaten for years suddenly seems to "get" you. That's why a generic food log often fails: it was built for calories, not for catching a reaction that depends on how much you ate and what you ate it with.
This guide is about the record itself. What to write down, at what level of detail, and why each field matters. It's built to pair with the blank food and symptom diary example.
Key takeaways
- Food intolerance is a digestive problem, not an immune reaction, and symptoms usually start a few hours after the food [1].
- Many intolerances are dose-dependent. For example, many people with lactose intolerance can handle about 12 grams of lactose, roughly a cup of milk, with mild or no symptoms [3][5].
- Hidden ingredients (milk solids, onion powder, sweeteners) cause a lot of "mystery" reactions [3][7].
- Log for 2–4 weeks without cutting foods first, so you have a baseline to compare against [9][10].
What should a food intolerance diary include?
A food intolerance diary is a daily, time-stamped record of everything you eat and drink, the ingredients and amounts, and any symptoms with their start time and severity. The NHS describes this kind of diary as one of the tools used, often with a dietitian, to work out what may be triggering symptoms [1].
Here's a three-level schema. Start at "minimum" if you're short on time; aim for "dietitian-ready" if you're going to book an appointment.
| Level | Food fields | Symptom fields | Context fields |
|---|---|---|---|
| Minimum | Time, dish, main ingredients | What, when it started | — |
| Better | + rough amount (cup, slice, handful), drinks including alcohol and coffee | + severity 0–10, how long it lasted | Sleep, stress 1–5 |
| Dietitian-ready | + sauces, dressings, cooking fat, sweeteners, brand of packaged foods, eaten out yes/no | + bowel movements with Bristol type, any medicine taken for it | + period day, exercise, new medicines or supplements |
IFFGD's diary takes a similar approach, tracking stool, pain, diet, medication, emotional state and exercise together over 2–4 weeks [9].
Why ingredients matter more than meal names
A single dish can contain three or four common intolerance suspects, and the diary needs to show which ones were there. "Chicken curry" might mean onion, garlic, cream, wheat naan and lentils. If you only write "curry", every one of them stays a suspect forever.
Here are the ingredients most worth naming every time, with where they hide:
| Ingredient | Common hiding places | Why it matters |
|---|---|---|
| Lactose (milk sugar) | Baked goods, processed meats, cereals, soups, salad dressings, snack chips, protein powders, nondairy creamers [3] | Labels may say whey, curds, milk by-products, dry milk solids or nonfat dry milk powder [3] |
| Fructans | Onion, garlic, leek, spring onion; wheat, rye and barley breads and pasta [7] | Onion and garlic powder turn up in stocks, spice mixes and sauces |
| GOS | Most beans and lentils, baked beans, falafel, split peas [7] | Often part of "healthy" swaps like chickpea pasta or lentil soup |
| Excess fructose | Apples, pears, mango, cherries, figs [7]; honey and juices | Juice and smoothies concentrate several servings |
| Polyols | Apples, stone fruits, mushrooms, celery [7]; sugar-free gum and sweets (sorbitol, xylitol) [7] | "Sugar-free" labels are a common surprise |
| Alcohol, caffeine, very fatty or spicy foods | Restaurant meals, takeout, cocktails | Can irritate the gut on their own, regardless of intolerance |
You don't need to memorize this. Just make it a habit to write the sauce, the bread and the drink, not only the "main" food.
Why timing and dose change everything
Two features make intolerance hard to spot: symptoms come late, and they scale with the amount.
Timing. The NHS says intolerance symptoms usually start a few hours after eating the food and can last a few hours or days [1]. With lactose, NIDDK says symptoms may appear within a few hours of having milk or milk products [2]. So your diary needs two times: when you ate, and when the symptom started. Then look back across the previous meals, and the day before, not only the last thing you ate. Our guide to how long after eating food intolerance symptoms start covers typical windows.
Dose. "Your symptoms may be mild or severe, depending on how much lactose you have," NIDDK notes [2]. A systematic review found moderate-quality evidence that most adults with lactose intolerance or malabsorption tolerate 12–15 g of lactose, about one cup of milk [5]. That explains a very common diary puzzle: a splash of milk in coffee is fine, a milkshake isn't.
Dose also adds up across a meal. Monash describes "FODMAP stacking": several small servings of FODMAP-containing foods eaten in one sitting can accumulate and trigger symptoms, even if each serving alone would be fine [8]. That's why rough portions belong in your diary.
Belief. It's worth recording honestly even when you're sure. An NIH consensus panel noted that many people who think they are lactose intolerant are not lactose malabsorbers [6]. A diary is how you check your own assumptions.
A sample food intolerance diary entry
Here's an illustrative four-day stretch for someone who suspects dairy. Notice how amount and context are logged. This is illustrative data, not a real case.
| Day | Food and drink (time, amount) | Dairy estimate | Symptoms (start, 0–10) | Stool | Context |
|---|---|---|---|---|---|
| 1 | 8:00 coffee with splash of milk · 12:30 cheddar sandwich (2 slices cheddar), apple · 19:00 salmon, rice, broccoli | Low | None | Next day type 4 | Slept 7.5 h |
| 2 | 8:00 large latte (whole milk, ~12 oz) · 12:30 leftover salmon, rice · 15:30 small yogurt · 19:00 chicken, potatoes | Moderate | 18:00 bloating 3/10 | Next day type 4 | Busy day |
| 3 | 8:00 cereal with 1.5 cups milk · 12:30 creamy tomato soup, bread · 20:00 ice cream (1 cup) | High | 11:00 gas 4/10; 22:00 cramps 6/10, bloating 6/10 | Next day 7:00 type 6 | Slept 7 h |
| 4 | 8:00 oatmeal with oat milk · 12:30 turkey wrap · 19:00 pasta with tomato sauce, parmesan | Low | Residual bloating 2/10 until noon | Same day type 5 | Slept 6 h |
What this suggests: symptoms tracked the amount of dairy, not just its presence. Hard cheese and a splash of milk caused nothing; a high-lactose day caused the worst symptoms and a looser stool the next morning. This is a pattern worth discussing with a doctor, who might suggest a hydrogen breath test or a period without milk products to see whether symptoms change [4]. It isn't a diagnosis. And it doesn't mean dairy needs to go: NIDDK notes yogurt and hard cheeses are lower in lactose, and that adding dairy a little at a time, with meals, can help [3].
For a whole filled-in week covering more than one suspect, see our food and symptom diary example.
How long should you keep a food intolerance diary?
Two to four weeks is a reasonable target. IFFGD recommends its daily diary for 2–4 weeks [9], and a Cleveland Clinic allergist suggests a food symptom journal kept for about a month, noting that patterns may take weeks to appear [10]. Eat normally while you log. Cutting foods before you have a baseline makes the diary harder to read.
Once you have a suspect, the next step is a structured test, ideally with a dietitian. Our guide to tracking an elimination diet explains how to log removal and reintroduction cleanly.
How to track food intolerance
The two habits that make the biggest difference are logging at the time you eat (memory loses sauces and amounts within hours) and logging symptoms when they start. Whatever tool you use:
- Capture each meal right away. A photo plus a few words ("cream sauce, garlic bread") is enough.
- Add rough amounts for anything you suspect.
- Log symptoms with a start time and a 0–10 score.
- Log stool with its Bristol type.
- Once a week, look back from each symptom across the previous 24–48 hours.
For ongoing records, explore the Get Regular food and symptom tracker. Check the current workflow, privacy information and access before entering sensitive information. A recorded association is a question to investigate, not a confirmed trigger.
When to see a doctor
Get medical advice rather than relying on a diary if you have:
- Blood in your stool, or black, tarry stools
- Unintended weight loss, persistent fever, or symptoms that wake you at night
- Ongoing diarrhea, severe pain, or a lasting change in bowel habit, especially if new after age 50
- A family history of celiac disease, inflammatory bowel disease or colon cancer
- Reactions within minutes of eating, hives, lip or throat swelling, or breathing trouble. These suggest a possible allergy, which needs an allergist, not a diary. Get emergency care for breathing problems.
Food intolerance symptoms can also overlap with IBS and other conditions; see IBS vs food intolerance for how they differ.
FAQ
What is the difference between a food allergy diary and a food intolerance diary? Allergy reactions are immune reactions that can be fast and dangerous, so suspected allergies need an allergist's assessment, not self-testing. An intolerance diary focuses on digestive symptoms over hours to days, which is why it emphasizes timing, amounts and context.
Do I need to weigh my food? No. Household measures (a cup, a slice, a handful) are enough to spot dose patterns. Weighing makes most people quit within a week.
Should I cut out the food I suspect while keeping the diary? Not at first. Log your normal diet for at least two weeks so you have a baseline. Then test one change at a time, preferably with a dietitian's guidance.
Is a food sensitivity journal the same as a food intolerance diary? In practice, yes. "Sensitivity" is a looser, non-medical term, but the method is the same: ingredients, timing, amount, symptoms and context.
Can a food diary diagnose food intolerance? No. It can show associations worth testing. Diagnosis comes from a clinician, sometimes with tests such as a hydrogen breath test for lactose [4] or a supervised elimination and reintroduction [1].
Sources
- NHS. Food intolerance. https://www.nhs.uk/conditions/food-intolerance/
- NIDDK. Symptoms & Causes of Lactose Intolerance. https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/symptoms-causes
- NIDDK. Eating, Diet, & Nutrition for Lactose Intolerance. https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/eating-diet-nutrition
- NIDDK. Diagnosis of Lactose Intolerance. https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/diagnosis
- Shaukat A, et al. Systematic review: effective management strategies for lactose intolerance. Ann Intern Med. 2010. https://pubmed.ncbi.nlm.nih.gov/20404262/
- Suchy FJ, et al. NIH consensus development conference statement: Lactose intolerance and health. 2010. https://pubmed.ncbi.nlm.nih.gov/20186234/
- Monash FODMAP. High and low FODMAP foods. https://www.monashfodmap.com/about-fodmap-and-ibs/high-and-low-fodmap-foods/
- Monash FODMAP Team. FODMAP Stacking Explained, 2022. https://www.monashfodmap.com/blog/fodmap-stacking-explained/
- IFFGD. Personal Daily Diary (IBS), publication #147. https://iffgd.org/resources/publication-library/personal-daily-diary-ibs/
- Cleveland Clinic. Do At-Home Food Sensitivity Tests Work? https://health.clevelandclinic.org/at-home-food-sensitivity-test
This article is for general education and isn't medical advice. Get Regular is a tracking app — it doesn't diagnose or treat any condition. If you have red-flag symptoms or ongoing changes in your digestion, talk to a doctor.