Fish Stock

High FODMAP

Typical portion

Any typical portion High

Fructans

Fish stock is High FODMAP, since most commercial versions are built on an onion and garlic base that carries right through into the liquid.

The Fructans from onion and garlic dissolve into the stock as it simmers, which pushes any typical portion into high territory even though the fish itself is a plain protein.
Store-bought stocks, cubes, and pastes almost always list onion or garlic among the first ingredients, so a quick label check tells you a lot before it goes in the pot.

For a low-FODMAP base, simmer your own fish stock using fish bones, herbs, and the green tops of spring onions, and reach for garlic-infused oil to build that savory depth.

Why fish stock is rated high

Fish stock is high FODMAP even though fish bones and shells contribute none. The usual recipe simmers them with onion, garlic and often leek bulb, and those aromatics carry fructans, which are water-soluble and move into the liquid during cooking. Fish stock simmers for a shorter time than meat stock, but that does not spare it: the fructans still leach out, and heat does not break them down. This rating is estimated from what the stock is made of rather than from a measured serving, and it sits at high for "Any typical portion". No lower rung exists, so the answer is a fish stock built without onion or garlic, not a smaller amount of the ordinary one.

What changes your risk

The aromatic base Onion, garlic and leek bulb are what make fish stock high. Fish frames, heads and prawn shells simmered without them give a stock without those fructans.
A short simmer is still long enough Fish stock cooks quickly, yet the fructans in the onion dissolve into the water all the same. Cooking time neither creates nor destroys them, so a quick stock is no gentler than a slow one.
Straining and clarifying A clear, well strained fish stock still holds every fructan that leached into it. Removing the solids only removes the vegetables, not what came out of them.
Seafood bases, cubes and powders Ready-made fish and seafood concentrates often list onion powder or garlic powder. Read the ingredient list, not the name on the front.
Stacking in seafood dishes Chowder thickened with wheat flour and cooked with onion, a seafood stew served with garlic bread, or a paella started with onion and garlic all pile more fructans onto the stock in the same meal.

Swaps

Make fish stock at home without onion or garlic: simmer white fish frames or prawn shells with leek leaves, the green tops of spring onions, carrot, parsley stems, bay leaf and peppercorns, then finish with garlic-infused oil. If no fish frames are to hand, a low FODMAP vegetable broth makes a reasonable base for a seafood risotto or stew, with the fish itself adding the sea flavour. When buying, look for a stock labelled onion- and garlic-free and check the ingredients. Do not reach for an ordinary vegetable stock or a shop-bought seafood bouillon as a gentler stand-in, since both usually start from the same onion and garlic.

How to lower the load

Ask a fishmonger for the frames and heads of mild white fish, rinse them well, and keep the simmer gentle and brief so the stock stays clean tasting rather than bitter. Sweat leek leaves and carrot in garlic-infused oil before adding the bones and cold water to build depth without onion. Strain through a fine sieve, cool quickly and freeze in labelled containers so it is ready for risotto, paella or a fish stew. Restaurant bouillabaisse, chowder, seafood risotto and paella almost always begin with onion and garlic, so ask before ordering.

Common questions

is fish stock low fodmap

No. Ordinary fish stock is high FODMAP at "Any typical portion", estimated from what it is made of, because the onion and garlic simmered with the bones release fructans into the liquid. Fish stock made without onion or garlic is the low option.

is seafood stock high in fructans

When it is made the usual way, yes. The fructans come from onion, garlic and often leek bulb in the pot, not from the fish or shellfish.

can i strain the onion out of fish stock to make it low fodmap

No. Fructans dissolve into the liquid as the stock cooks, so straining out the onion afterwards leaves them behind. Onion and garlic need to stay out of the pot from the start.

what can i use instead of fish stock on low fodmap

A homemade stock of fish frames or prawn shells simmered with leek leaves, spring onion greens, carrot and herbs, finished with garlic-infused oil, or a product labelled onion- and garlic-free. A homemade low FODMAP vegetable broth also works as a base when the dish has plenty of fish in it.

Learn more

Informational only, not medical advice. Individual tolerance varies. Talk to a healthcare professional or a dietitian for personal guidance.

Fish Stock is an estimated rating: it is inferred from the food's ingredients and composition and cross-checked, not measured directly in the papers below. The low, moderate and high cutoffs are still those of Varney et al. (2017).

References

Fructan and free fructose content of common Australian vegetables and fruit. Muir et al. (2007), J. Agricultural and Food Chemistry 55(16):6619-6627.
Measurement of short-chain carbohydrates in common Australian vegetables and fruits by HPLC. Muir et al. (2009), J. Agricultural and Food Chemistry 57(2):554-565.
Quantification of fructans, galacto-oligosaccharides and other short-chain carbohydrates in processed grains and cereals. Biesiekierski et al. (2011), J. Human Nutrition and Dietetics 24(2):154-176.
Dietary sorbitol and mannitol: food content and distinct absorption patterns. Yao et al. (2014), J. Human Nutrition and Dietetics 27(Suppl 2):263-275.
FODMAPs: food composition, defining cutoff values and international application. Varney et al. (2017), J. Gastroenterology and Hepatology 32(Suppl 1):53-61. Supplies the low, moderate and high cutoffs used on this page.