The low-FODMAP diet, explained
Reviewed August 2026
FODMAP is short for fermentable oligosaccharides, disaccharides, monosaccharides and polyols — a group of short-chain carbohydrates that some guts struggle to absorb. When they aren't absorbed, they draw water into the small intestine and ferment in the large intestine, producing the gas, bloating and cramps many people feel a few hours after a meal.
The five kinds of FODMAP
There are five groups: • Fructans — in wheat, onion and garlic. • Galacto-oligosaccharides (GOS) — in beans, lentils and chickpeas. • Lactose — in milk, soft cheese and yoghurt. • Excess fructose — in apples, honey and mango. • Polyols such as sorbitol and mannitol — in stone fruit, mushrooms and ‘sugar-free’ sweeteners. Most people tolerate these without symptoms. In a sensitive gut, usually only one or two groups are the real culprits — which is why finding your personal triggers matters far more than avoiding everything.
Why FODMAPs cause bloating and gas
Two things happen at once. Some FODMAPs pull water into the small intestine (an osmotic effect); others reach the large intestine undigested, where gut bacteria ferment them and release gas. Together that stretches the bowel wall — and in a sensitive gut, that stretch is felt as bloating, cramping, wind or an urgent trip to the bathroom, usually a few hours after eating.
The hidden triggers a barcode can't see
The hardest FODMAPs to catch aren't printed on any label. Onion and garlic — both high in fructans — hide in sauces, stocks, dressings, marinades and spice blends, in small amounts that still set off symptoms. A packaged-food barcode scanner never sees them, and a restaurant menu certainly won't list them. This is the exact gap Rumbelly is built for: photograph a cooked meal or a menu and it flags the likely hidden triggers before you eat.
The low-FODMAP approach
The low-FODMAP approach was developed by researchers at Monash University in Australia, and it is not meant to be permanent. It works in three stages: a short elimination phase to calm symptoms, a structured reintroduction phase that tests each FODMAP group one at a time, and a personalisation phase where you keep only the restrictions you actually need. Because it temporarily cuts out whole food groups, it is best done with the guidance of a doctor or dietitian rather than indefinitely on your own.
Common questions about FODMAPs
- Are FODMAPs bad for you?
- No. For most people FODMAPs are healthy — many act as prebiotics that feed good gut bacteria. They are only a problem for people whose guts are sensitive to them, such as many people living with IBS.
- Is a low-FODMAP diet forever?
- No. The elimination phase is a short, temporary starting phase, not a lifelong diet. The goal is to reintroduce as many foods as you can and keep only the few restrictions you genuinely need.
- Which foods are highest in FODMAPs?
- Common high-FODMAP foods include wheat, onion, garlic, beans and lentils, milk and soft cheese, apples, pears, honey, mushrooms, and ‘sugar-free’ sweeteners like sorbitol and mannitol.
- Can an app find my triggers for me?
- An app can help you spot patterns between what you eat and how you feel, and flag likely hidden triggers — but it can't diagnose you. Rumbelly is an educational tool, not a medical device; bring your data to a doctor or dietitian.
This guide is educational and isn't medical advice. If gut symptoms are affecting your daily life, talk to a doctor or dietitian.