The low FODMAP diet: a beginner's guide
The low FODMAP diet is one of the best-studied dietary approaches for irritable bowel syndrome (IBS). It is not a forever diet. It is a short, structured experiment to find out which foods you react to, so you can eat as freely as possible.
What are FODMAPs?
FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. These are short-chain carbohydrates that the small intestine absorbs poorly. They move on to the large intestine, where gut bacteria ferment them and they draw in water. For many people with IBS, that leads to bloating, gas, pain and changes in bowel habits.
| Group | What it is | Common sources |
|---|---|---|
| Fructans | Oligosaccharide | Wheat, garlic, onion |
| GOS | Oligosaccharide | Beans, lentils, chickpeas |
| Lactose | Disaccharide | Milk, soft cheese, yogurt |
| Excess fructose | Monosaccharide | Apples, mango, honey |
| Polyols | Sugar alcohols | Stone fruit, mushrooms, sorbitol and mannitol sweeteners |
FODMAPs are not “bad” foods. Many are good for gut bacteria. The point of the diet is to find your personal threshold, not to avoid them for life.
The three phases
1. Elimination (about 2 to 6 weeks)
Swap high FODMAP foods for low FODMAP alternatives and watch how your symptoms change. If symptoms improve clearly, FODMAPs are likely part of the picture. If nothing changes after a few weeks, the diet may not be the right tool for you, and that is useful information too.
2. Reintroduction (about 6 to 8 weeks)
Test one FODMAP group at a time with gradually larger portions, while keeping the rest of your diet low FODMAP. This tells you which groups you tolerate, and how much of them. Read our reintroduction guide for the step-by-step method.
3. Personalization (long term)
Bring back every food you tolerate and limit only the ones that clearly cause symptoms. Most people end up with a far more varied diet than during elimination.
Tips that make it work
- Work with a dietitian. A registered dietitian trained in the low FODMAP diet improves results and helps you avoid unnecessary restriction.
- Serving size matters. Many foods are low FODMAP in small portions and high in large ones. The Monash University FODMAP app lists tested serving sizes.
- Keep a food and symptom diary. It turns vague impressions into evidence you can act on. See how to keep a food and symptom diary for IBS.
- Do not self-diagnose. Symptoms like weight loss, blood in your stool or symptoms that wake you at night need a doctor first.
Check a food
Wondering about a specific ingredient? Start with the FODMAP food guide, for example garlic or onion, two of the most common hidden triggers.