Guide · 8 min read

IBS food diary: find patterns without guessing

With irritable bowel syndrome, the same food can feel fine one day and terrible the next. A food and symptom diary is the most practical way to see what really affects you. Here is how to keep one, how FODMAPs fit in and how to read it honestly.

By Caspar Baumeister · Updated 13 October 2026

Why an IBS food diary helps

IBS triggers are personal. One person reacts to onions, another to coffee or stress, a third to large fatty meals. The NHS advice is simple: keep a diary of what you eat and any symptoms you get, to find out what triggers your IBS. A diary also helps your doctor or dietitian decide what to try next, and it protects you from cutting out foods for no good reason.

What to log

Meals and drinks: what, roughly how much, and when. Note snacks, coffee, alcohol and sugar free products too.
FODMAP groups: tag meals with the groups they contain (see the table below). That makes patterns visible across very different dishes.
Symptoms: bloating, cramps, gas, urgency, nausea, heartburn, tiredness, each with a rough strength from 1 to 10.
Bowel movements: time and Bristol type. IBS with constipation, with diarrhea and the mixed type look very different on paper.
Context: sleep, stress, exercise, your period and any medicines.

FODMAP basics, and a short FODMAP list

FODMAPs are short chain carbohydrates that the small intestine does not absorb well. Gut bacteria ferment them, which produces gas and draws water into the bowel. In people with IBS, that can mean bloating, pain and changes in stool. The name stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols.

The five FODMAP groups with common high FODMAP foods (based on Monash University)
Group	Type	Common sources
Fructans	Oligosaccharides	Wheat, rye, barley, onion, garlic, leek
GOS	Oligosaccharides	Beans, lentils, chickpeas, some nuts
Lactose	Disaccharide	Milk, soft cheese, yoghurt, cream
Excess fructose	Monosaccharide	Honey, apples, pears, mango, agave syrup
Polyols	Sugar alcohols such as sorbitol and mannitol	Stone fruit, mushrooms, cauliflower, sugar free sweets and gum

Foods that are commonly low in FODMAPs at normal portions include rice, oats, potatoes, carrots, cucumber, tomatoes, eggs, firm tofu, meat and fish, hard cheese, lactose free milk, oranges, kiwi and strawberries. Portion size changes everything, though: some foods are fine in a small serving and high in a large one. Monash University, which developed the low FODMAP diet, publishes lab tested portion data in its own app.

How the low FODMAP diet works

It is a short learning diet, not a diet for life. According to Monash, a period of strict reduction for 2 to 6 weeks is followed by reintroducing foods step by step to find out which groups you tolerate, and then a personal, as varied as possible diet. Studies such as Halmos et al. in Gastroenterology (2014) found that many people with IBS have fewer symptoms on it. It does not help everyone: Monash reports that about 1 in 4 people with IBS do not improve. Monash recommends doing it with a dietitian or other health professional, and only after IBS has been diagnosed. The NIDDK also suggests talking with a dietitian.

An example day

Example entries in an IBS food diary
Time	Entry	Notes
07:30	Oats with lactose free milk, kiwi, coffee	Slept 6 hours, busy day ahead
08:10	Bowel movement, Bristol type 4	Easy
12:45	Wholewheat pasta with garlic and onion sauce	Tags: fructans
16:00	Bloating 6 of 10, cramps 3 of 10	Stressful meeting at 15:00
21:00	Bowel movement, Bristol type 6	Urgent

Was it the fructans, the stress or the short night? One day cannot tell. The same pattern after several similar meals, while days without them feel better, can.

How to read your diary honestly

Give it time. Symptoms do not always follow the last meal. Tummi, for example, compares each meal tag with how you felt 12 to 48 hours later.
Compare with and without. A food only looks suspicious if days with it go worse than days without it.
Wait for enough data. Two or three meals are not enough. Patience protects you from avoiding foods you actually tolerate.
A pattern is not a diagnosis. Treat it as a question to bring to your doctor or dietitian, not as a verdict.
Do not cut out lots of foods on your own. The NHS advises seeing a GP if you find yourself avoiding many foods. They can refer you to a dietitian.

Signs that need a doctor, not a diary

IBS is diagnosed only after other conditions are ruled out. Weight loss without trying, blood in the stool, fever, anaemia or paleness, symptoms that wake you at night and new symptoms later in life are not typical for IBS. Coeliac disease, inflammatory bowel disease and other conditions can feel similar, so please get these checked.

How Tummi helps with an IBS food diary

Tummi screen: patterns after meals, comparing meal tags like onion and garlic with how you felt 12 to 48 hours later — Patterns after meals and weekly insights are part of Tummi Plus.

Tummi screen: weekly insights with comfort trend, average Bristol type, days without and longest gap — Patterns after meals and weekly insights are part of Tummi Plus.

In Tummi you log meals with the five FODMAP groups and common suspects like coffee, gluten, dairy, alcohol or spicy food, together with symptoms and bowel movements. With Tummi Plus, the app compares each tag with how you felt 12 to 48 hours later, against all meals without it. It only shows "noticed more often" after at least three meals and a clear difference, and otherwise says honestly that there is not enough data yet. Everything stays on your iPhone.

When not to wait

Get help right away

Call 999 in the UK, 911 in the US, 112 in the EU or your local emergency number if you have:

a lot of blood, or black and tarry stool with dizziness or weakness
severe belly pain that does not ease
a hard, swollen belly with vomiting, and you cannot pass wind or stool
signs of dehydration with diarrhea, like very little urine or confusion

Get an urgent appointment the same day

if your stool is black or dark red, or you have bloody diarrhea (in the UK: urgent GP appointment or NHS 111)

See a doctor soon if

you see blood in or on your stool
your bowel habits change and stay changed for 3 weeks or more
constipation does not get better with self-care or keeps coming back
diarrhea lasts longer than a week
you lose weight without trying or feel very tired
your stool is pale or clay coloured, or your skin or eyes turn yellow
pain wakes you up at night
your child is constipated for more than a few days or it hurts

Frequently asked questions

How long should I keep an IBS food diary?

At least two to four weeks. Many symptoms appear hours or a day after eating, and you need several similar meals before a pattern means anything.

Should I try the low FODMAP diet on my own?

Monash University recommends doing it with a dietitian or other health professional, and only after IBS has been diagnosed. It is a short learning diet with reintroduction, not a permanent diet.

What are the most common IBS trigger foods?

The NHS mentions fatty, spicy and processed food, caffeine, alcohol, fizzy drinks, the sweetener sorbitol and foods that are hard to digest like beans, cabbage and onions. Triggers are personal, which is why a diary helps.

Can stress trigger IBS symptoms?

Yes, for many people. The gut and brain influence each other. That is why it helps to note stress and sleep in your diary along with food.

What is a FODMAP list?

A list of foods grouped by their FODMAP content. The five groups are fructans, GOS, lactose, excess fructose and polyols. Portion size matters a lot, so lab tested data from Monash University is the most reliable reference.