Leek

Leeks are an allium, like onion and garlic, and they store fructans (a fermentable fiber) in their bulb. For people with IBS or fructan intolerance, leek bulb can produce the same bloating, gas, and abdominal pain that onion does — and like other fructans, cooking does not break them down. Long-simmered leek and potato soup is just as triggering as raw.

White vs green parts

The fructans concentrate in the white bulb. The dark green tops (often discarded as "tough") are low-FODMAP at typical portions and contribute most of the allium flavor — slice them thin and add at the end of cooking. This split lets people who can't tolerate onion or garlic still get leek-like flavor into stocks, soups, and sautés.

When leek is a hidden trigger

Restaurant stocks, "vegetable broth," and store-bought soups frequently use leek bulb. If avoiding onion and garlic has only partly resolved symptoms, leek is the next allium to suspect. A registered dietitian familiar with FODMAPs can help structure the low-FODMAP elimination and reintroduction properly.