Irritable bowel syndrome (IBS) is a complex digestive condition with abdominal pain, gas, bloating, nausea and alternating constipation and diarrhea. Food does not cause the syndrome, but it can worsen or ease the symptoms. The FODMAP diet is one of the most studied strategies for this, and it is done in stages, with guidance.
In short
- FODMAPs are fermentable carbohydrates that some people absorb poorly and that gut bacteria ferment, causing gas and discomfort.
- The diet is temporary: elimination for 2 to 6 weeks, reintroduction by group, then personalization.
- The goal is not to cut everything forever, but to find each person's limit.
- Before starting, it is important to rule out other causes of symptoms, such as celiac disease.
01
Before the diet: the basics
Some habits worsen irritable bowel symptoms and deserve attention before any restriction:
- Large amounts of simple sugars and heavily sweetened drinks.
- Dehydration and low water intake.
- Too much fiber at once, or too much fat and greasy food.
- Too much caffeine and alcohol.
- Artificial sweeteners and “diet” and “light” products, which may contain polyols.
- Some supplements, such as sodium bicarbonate and citrate.
- Eating too fast: chew well, since digestion starts in the mouth.
- Dairy, in people with milk allergy or lactose intolerance.
Persistent digestive symptoms need medical evaluation. Celiac disease, inflammatory bowel disease, SIBO and other conditions can cause similar symptoms and should be investigated before a restrictive diet, which can get in the way of testing.
02
What FODMAPs are
FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. They are short-chain carbohydrates that, when not well digested and absorbed, reach the large intestine, draw in water and are fermented by bacteria, producing gas and, in sensitive people, pain, bloating and changes in bowel habit.
Lactose (disaccharide)
Milk, yogurt, fresh cheeses, cream cheese and ice cream. Aged cheeses and lactose-free dairy are usually better tolerated.
Excess fructose (monosaccharide)
Honey, corn syrup, mango, pear, apple, watermelon, fig, grape, prunes and drinks sweetened with fructose syrup, such as many soft drinks.
Fructans (oligosaccharide)
Wheat, rye and barley, onion, garlic, leek, artichoke, beetroot and inulin added to some products. Wheat is the largest source of fructans in the diet, and the problem is not gluten.
Galactans (oligosaccharide)
Legumes such as beans, lentils, chickpeas and soy. Small portions and canned legumes, well rinsed, are usually better tolerated.
Polyols
Sorbitol, mannitol, xylitol, maltitol and isomalt, found in candy, gummies, chewing gum, lozenges, diet products and some medicines, and naturally in avocado, cherry, peach, nectarine, apricot, plum, mushrooms and cauliflower.
FODMAPs are not “bad foods”: many are nutritious and feed beneficial bacteria. The issue is how much each person tolerates, and reactivity depends on the dose.
03
The three phases of the diet
Phase 1: elimination (2 to 6 weeks)
Reduces foods rich in FODMAPs to see whether symptoms improve. It is not a diet for life and should not last longer than needed: if there is no improvement in 4 to 6 weeks, it is probably not the answer and should be stopped. Avoid starting without guidance, since it is easy to end up with a diet low in fiber and nutrients.
Phase 2: reintroduction (about 6 to 8 weeks)
Once symptoms improve, reintroduce one group of FODMAPs at a time to find out which ones cause symptoms. Do not test everything at once, or it will not be possible to tell which food was responsible.
Phase 3: personalization
With what you have learned, the diet becomes as varied as possible again. Foods that cause trouble are limited or eaten in small portions, and well-tolerated foods return to the menu.
04
How to do the reintroduction
A model used in practice: test a single group per week (lactose, fructose, fructans, galactans and polyols), in increasing portions.
- Monday: a small portion of the food being tested.
- Wednesday: a medium portion.
- Friday: a larger portion.
- On the other days, go back to the low-FODMAP diet and watch your symptoms.
- Keep a diary of what you ate, how much and your symptoms.
Reactivity depends on the dose: some people tolerate all three portions, others react to the first. If symptoms appear, the food should be avoided or eaten only occasionally and in small amounts.
Between test weeks, return to the low-FODMAP diet to avoid carry-over effects. After testing all groups, combine those that were well tolerated in one meal to assess tolerance to a varied diet.
If you have many symptoms after a meal, the cause may be the sum of several FODMAPs at once, and not a single food on its own.
05
Swaps that help in the elimination phase
Grains
Swap wheat bread and pasta for rice, quinoa, a small portion of oats, tapioca, corn couscous, polenta and potato. Long-fermented bread and wheat-free products can also be options. You do not need to remove gluten itself, only the fructans in wheat.
Seasoning
Use fresh herbs, spring onion (green part only), garlic-infused oil and flavored olive oil. Garlic and onion pieces appear in ready-made sauces and stock: read the label.
Fruit
Ripe banana in a small portion, orange, mandarin, strawberry, kiwi, grapes (small portion) and pineapple are usually well tolerated.
Dairy
Lactose-free versions, aged cheeses and plant drinks with no added inulin or polyols.
Protein and vegetables
Meat, fish, eggs and firm tofu; carrot, zucchini, cucumber, tomato, potato, spinach and lettuce are generally well tolerated.
Food lists vary with portion size and analysis method. That is why follow-up with a nutritionist and up-to-date sources, such as the Monash University app, help avoid unnecessary restrictions.
06
Important cautions
- A prolonged restrictive diet can reduce fiber, calcium and microbiome diversity. That is why it should not become permanent.
- Do not use the diet to lose weight or in people with a history of eating disorders without specialized follow-up.
- Avoid large amounts at once and chew slowly. Stress, poor sleep and inactivity also affect symptoms.
- Probiotics, enzymes and other tools may help some people, but the choice should be individualized.
Some studies link lactose and fructose malabsorption to symptoms outside the gut, such as mood changes. This relationship is not yet well established and should not lead to restrictions on your own.
Find out what your gut tolerates
In the consultation, I assess symptoms, tests, history and routine to guide the three phases of the diet safely, avoiding unnecessary restrictions and following your response, together with your doctor.
Dra. Daniely Catharino TooleyClinical, functional and orthomolecular nutritionist · CRN3/6794
References (5)+
- Monash University. The Monash University Low FODMAP Diet; FODMAP Friendly app.
- Halmos et al. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology, 2014.
- Black et al. Effectiveness of a low FODMAP diet in IBS: systematic review and network meta-analysis. Gut, 2022.
- ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol, 2021.
- NICE. Irritable bowel syndrome in adults: diagnosis and management (CG61).
Educational content for adults. This guidance does not replace an individual consultation, diagnosis or treatment.