Leek
Vegetables · Alliums
A leek is two ingredients on one stalk, and only one of them is usable. A quarter leek cut through the white bulb, 50 g, is rated red on 0.5 g of fructans, while the dark green leaves are listed separately in this guide and rated green. Even so, the leaves-only serve tested on this entry comes out amber at 10 g, so the safe part is narrower than it first looks.
Last updated 3 September 2026Serving sizes for leek
Leaves only at 10 g rates amber. A quarter leek with the bulb (50 g) is rated red.
Tested serving sizes
| Serving | Amount | Main FODMAP | Rating |
|---|---|---|---|
| Small amount (leaves only) | 10 g | Fructans 0.1 g | |
| 1/4 leek with bulb | 50 g | Fructans 0.5 g |
Breakdown for 10 g
Is leek low FODMAP?
Fructans are the only group leeks carry in quantity, and they concentrate in the white bulb rather than in the leaves. That is why a quarter leek taken through the bulb reaches 0.5 g of fructans, while a small amount of leaves alone shows 0.1 g, sitting right on the level where fructans begin to count. For scale, one small clove of garlic packs 0.53 g of fructans into 3 g. A quarter leek delivers a clove’s worth of fructans spread over about sixteen times the weight, which is exactly why it slips past unnoticed in a soup.
Leek and IBS: what to know
In practice the split is a knife decision: keep the dark green tops, put the pale bulb aside, and wash the tops carefully because grit hides between the layers. Fructans are water-soluble, so a leek simmered in stock passes them straight into the broth, and lifting the pieces out later does not rescue the liquid. They do not dissolve into fat, which is why garlic-infused oil is safe while the solids it was made from are not. If leek has always been in your cooking, this is the habit worth changing first.
Gut-friendly ways to eat leek
Rebuild the allium base rather than shrink the leek. Sliced leek greens, chives and the green tops of spring onion softened in garlic-infused oil give a soup, risotto or omelette the savoury depth people miss most when onion comes off the menu. Where a recipe calls for one whole leek, use the greens of two and add a pinch of asafoetida for the sulphurous note. Keep the white bulbs for someone else in the house, or for a stock you are not going to drink.
Frequently asked questions
Which part of a leek is low FODMAP?
The dark green leaves. Fructans build up in the white bulb, so a quarter leek that includes it is rated red. The leaves have their own entry in this guide, rated green, though the leaves-only serve tested on this page still comes out amber, so the green rating belongs to the dark tops specifically rather than to anything pale or tender near the base.
Is leek better than onion for IBS?
Only if you use the right part. One tablespoon of chopped onion, 10 g, is rated red with 0.4 g of fructans, while the same weight of leek leaves rates amber with 0.1 g. That is a real difference, and it disappears the moment the bulb goes in the pan, because a quarter leek matches the fructan load of a small garlic clove.
Can I use leek in soup?
Use the green tops and add them near the end. Because fructans dissolve into water, anything simmered with the bulb leaves them in the bowl, which is what makes leek and potato soup so hard to rebuild. Sweat the greens in garlic-infused oil for the base and build on potato, which carries only 0.02 g of fructans in one medium potato.
What can I use instead of leek?
Leek greens are the first answer, since they are the same flavour from the same plant. Chives and the green parts of spring onion cover the fresh, mild oniony note in eggs, potatoes and dressings. For the body a leek gives a soup, slowly softened carrot or celeriac does a similar job, and both are rated green here. Garlic-infused oil handles the deeper savoury layer the bulb was providing.
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