Fish Sauce

Low FODMAP

Typical portion

Any typical portion Low

Fish sauce is Low FODMAP, a simple ferment of fish and salt with almost no carbohydrate to cause trouble.

Made from just fermented fish and salt, with no onion or garlic and negligible carbohydrate, so it stays low at any typical splash you would add to a dish.
It brings a big savory punch for a tiny amount, which makes it an easy way to build depth without reaching for high-FODMAP aromatics; just check the label since some blends slip in extra ingredients.

Use it in place of stock cubes or garlic-heavy sauces to add umami, and pair it with garlic-infused oil for that classic savory base.

Why fish sauce is rated low

Fish sauce is low, and that call is an estimate based on what it is made of rather than a weighed laboratory serving. Traditional fish sauce is fish and salt left to ferment, which leaves almost no carbohydrate behind for the gut to ferment, and none of the six FODMAP subgroups is recorded for it. The ladder has a single rung, Any typical portion, and it reads low, so the splash or two that a dish actually calls for is not the thing to worry about. Low here describes the bottle's normal ingredient list, though, so the practical question is not how much fish sauce but which fish sauce, because blended and flavoured versions can carry ingredients the plain ferment does not.

What changes your risk

The ingredient list on the bottle Plain fish sauce is anchovy or another fish plus salt, and sometimes sugar. Products sold as seasoning sauce, stir fry sauce or a fish sauce blend can add garlic, onion, shallot, garlic powder or a syrup, and that changes the picture entirely. The short ingredient list is the one to buy.
What it gets mixed into Fish sauce rarely arrives alone. Dipping sauces such as nuoc cham and most Thai and Vietnamese marinades are fish sauce plus minced garlic and shallot, so the sauce on the table can be high even though the bottle behind it is low. Mix your own with fish sauce, lime, sugar, chilli and garlic-infused oil.
Portion in practice Any typical portion is recorded as low, and the salt does the portioning for you, since a dish seasoned past a splash or two becomes too salty to eat. There is no reason to measure it, but it is also not an ingredient to pour with a free hand.
Stacking across the meal A low rating is per serving, not per meal. Fish sauce contributes essentially nothing itself, so the total load of a meal comes from everything around it: the noodles, the vegetables, the fruit in the dressing. Spreading those servings out matters more than the sauce ever will.

What else works

Fish sauce is one of the better tools on this diet, because it delivers the savoury depth people usually chase with onion and garlic. Alongside it, garlic-infused oil, chives, the green tops of spring onions, leek leaves and a pinch of asafoetida all build that same base, and plain soy sauce or tamari covers similar ground. The lookalikes worth avoiding are the ones that share the shelf: oyster sauce, hoisin, most stir fry and seasoning sauces, and powdered or cubed stock bases are commonly built on onion and garlic, and a jarred nuoc cham or fish sauce dressing usually has raw garlic and shallot in it. Anchovy paste is a closer cousin in flavour, though it too is worth checking for added aromatics.

How to keep it low

Look for a bottle whose label reads close to anchovy, salt and water, and nothing else. Colour is a rough guide worth knowing: a clear reddish brown sauce is usually a first press ferment, while a very dark, syrupy one is more often a blend with additions. Once open, fish sauce keeps for a long time in a cool dark cupboard, and the fridge slows the darkening if you use it slowly. Add it near the end of cooking so the aroma stays bright, and use it to replace the stock cube or the garlic in a recipe rather than as an extra on top. Eating out, the sauce on the table is the risk, not the cooking: ask whether the dipping sauce has garlic or shallot in it, and ask for lime and chilli on the side instead.

Common questions

is fish sauce low fodmap

Yes. Fish sauce is rated low overall, estimated from its composition as a simple ferment of fish and salt rather than from a measured serving, and Any typical portion is recorded as low.

how much fish sauce can i use

Any typical portion is the rung recorded, and it reads low, so the amount a recipe calls for is not the concern. Its saltiness keeps portions small on its own.

does fish sauce have onion or garlic in it

Traditional fish sauce does not, but blends and seasoning sauces sometimes do. Check the label for garlic, shallot, onion or onion powder, and prefer a bottle whose ingredients are just fish and salt.

can i eat fish sauce on the elimination phase

Plain fish sauce suits the elimination phase, and it is a useful way to add savoury depth without onion or garlic. Watch the dipping sauces and marinades built on it, since those usually add both.

Learn more

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

Fish Sauce 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.