How to keep a food diary for IBS

Updated October 5, 2026 by Kamal Nasir

Write down what you eat and drink, when, and roughly how much, then record each symptom with its time and severity, plus your bowel movements. The NIDDK, part of the National Institutes of Health, says you may need to change what you eat for several weeks to see whether symptoms improve, and the International Foundation for Gastrointestinal Disorders (IFFGD) suggests a diary of food, symptoms, stress, sleep and medicines for 2 to 3 weeks to help identify trigger foods. Give it several weeks, because one bad day after a meal proves very little.

General information, not medical advice. How these guides are made.

Get a diagnosis first

IBS symptoms overlap with other conditions. Monash University, whose researchers developed the low FODMAP diet, warns against self-diagnosing IBS because celiac disease, inflammatory bowel disease, endometriosis and bowel cancer can cause similar symptoms. The NIDDK says to talk to your doctor if your symptoms are like those of IBS. A doctor may diagnose it when symptoms have come at least once a week for the last 3 months and first started at least 6 months ago, or sooner in some cases.

What to record for every meal and snack

• The time you ate
• Everything in it, including sauces, seasonings, drinks and sweeteners. The NIDDK lists garlic salt and candy or gum with sweeteners ending in -ol, such as sorbitol, among foods that contain FODMAPs.
• Roughly how much. Monash rates a food as low, moderate or high in FODMAPs by serving size, so the same food can count differently in a small and a large portion.
• Alcohol and caffeine: the IFFGD says coffee, caffeine and alcohol, like meals that are too large or high in fat, may provoke cramps and diarrhea

IBS Tracker Food Diary: Fennel

IBS food diary and symptom tracker

Get it on the App StoreAbout the app

What to record for symptoms and bowel movements

• Each symptom and the time it started: belly pain or cramps, bloating, diarrhea or constipation, the main symptoms the American College of Gastroenterology (ACG) lists, and gas
• How bad it was, on a simple scale such as 0 to 10, so you can compare days
• Each bowel movement: the time, and whether the stool was hard, normal, loose or watery
• Stress and anxiety, which the ACG says can worsen symptoms, and which the Monash diary also records
• Anything else that changed, such as a new medicine or a recent infection, both of which the NIDDK says your doctor will ask about

How to read your diary without fooling yourself

The common trap is blaming the last thing you ate. A fairer test asks two questions: how often did symptoms follow on days you ate a food, and how often did they come on days you did not? If symptoms are just as common either way, the food is probably not the link. The IFFGD also notes that people with IBS often find a food bothers them at some times but not at others.

Look at groups as well as single foods. Monash groups FODMAPs into fructans and GOS (in foods such as wheat, rye, onions, garlic and legumes), lactose (milk, soft cheeses and yogurt), fructose (honey, apples, high fructose corn syrup) and the polyols sorbitol and mannitol. Several foods from one group on the same day can add up.

Then take the diary to a professional. The IFFGD says diets that restrict many types of food should be guided by a dietitian, and the ACG says a dietitian is often helpful because these diets can be complicated and limiting.

From diary to diet changes

Avoid cutting out whole food groups on your own. If a dietitian suggests a low FODMAP diet, Monash describes three steps: 2 to 6 weeks of low FODMAP eating, a reintroduction step that tests one FODMAP group at a time, and a personalized long-term diet. Your diary is what makes the second step readable. Monash also says about one in four people with IBS do not improve on the diet and need other approaches, which is a conversation for your doctor.

Symptoms that need a doctor soon

The NIDDK says some symptoms may point to a health problem other than IBS: bleeding from your rectum, bloody stools or stools that are black and tarry, weight loss, and anemia. The ACG lists unexplained weight loss, low iron levels, symptoms that start later in life and a family history of colon cancer as warning signs that may call for tests such as a colonoscopy. The NHS, the UK health service, also lists a hard lump or swelling in your belly as a reason for an urgent appointment. Do not wait for a pattern to emerge in your diary before getting any of these checked.

Keeping the diary on your phone

Fennel, an IBS food diary and symptom tracker for iPhone, logs a meal in seconds, a symptom in three taps and stool in two. It compares the days you ate a food with the days you did not, inside fixed time windows, and reports how often symptoms followed, by food and by FODMAP group, with the days and counts behind every reading. It reports nothing until there is enough data, and it never tells you to avoid a food; what to do about a pattern is for you and your clinician.

Questions people ask

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• IBS Tracker Food Diary: Fennel