The FODMAP groups
The six FODMAP groups, explained
FODMAP is an acronym for six families of fermentable carbohydrates that can trigger IBS symptoms: fructans, galacto-oligosaccharides (GOS), lactose, excess fructose, sorbitol, and mannitol. Most people react to only a few of them — which is the whole point of testing them one at a time. Start with a group below to see what it is, the foods that carry it, and how it's reintroduced.
Fructans
Fructans are chains of fructose molecules — an oligosaccharide and the most common FODMAP trigger. No one produces the enzyme to break them down, so they ferment in the colon. The classic fructan foods are wheat, rye, onion, and garlic, which is why fructan intolerance is so often mistaken for gluten sensitivity.
Explore fructans →FODMAP group · OligosaccharidesGOS
GOS — galacto-oligosaccharides — are short chains of galactose sugars, an oligosaccharide FODMAP. Like fructans, human enzymes can't break them down, so they ferment in the colon. The classic GOS foods are legumes: chickpeas, lentils, and kidney beans, along with cashews, pistachios, and some legume-based plant milks.
Explore gos →FODMAP group · DisaccharideLactose
Lactose is the natural sugar in milk — a disaccharide of glucose and galactose. It needs the enzyme lactase to be absorbed; when lactase is low, undigested lactose draws water into the gut and ferments. Milk, soft cheeses, yoghurt, and ice cream are the classic high-lactose foods, and lactose is a common, easily tested IBS contributor.
Explore lactose →FODMAP group · MonosaccharideExcess fructose
Excess fructose means a food holds more fructose than glucose. Fructose is absorbed slowly on its own, so when it outstrips glucose the surplus ferments in the gut — often called fructose malabsorption. Honey, apples, pears, mango, and high-fructose corn syrup are the foods most likely to carry excess fructose.
Explore excess fructose →FODMAP group · PolyolSorbitol
Sorbitol is a polyol — a sugar alcohol — poorly absorbed by everyone. Unabsorbed sorbitol pulls water into the bowel and ferments in the colon. It occurs naturally in stone fruit, apples, and pears, and is added to sugar-free gum, mints, and 'diet' products as the sweetener E420, a frequent hidden trigger.
Explore sorbitol →FODMAP group · PolyolMannitol
Mannitol is a polyol — a sugar alcohol closely related to sorbitol and just as poorly absorbed. Unabsorbed mannitol draws water into the intestine and ferments in the colon. Its classic food sources are mushrooms, cauliflower, celery, and sweet potato, and it also appears as the added sweetener E421 in sugar-free products.
Explore mannitol →Why the groups matter
Elimination tells you that FODMAPs affect your gut. It doesn't tell you which ones. The reintroduction phase tests each group in turn so you can rebuild the widest diet your gut allows — see our guide to FODMAP reintroduction for the full method, or the overview of the three-phase diet.