Fish Sauce

Why fish sauce is rated low

Fish sauce is low at about 1 tablespoon (20mL), moderate at larger portions and high at much larger portions. Traditional fish sauce is fish and salt left to ferment, which leaves very little carbohydrate behind; the small amounts of GOS and mannitol it carries only build when the pour grows well past a splash. A tablespoon covers what most dishes call for, so quantity is rarely the thing to worry about. Low here describes the bottle's normal ingredient list, though, so the practical question is not only 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 About 1 tablespoon (20mL) is low, and larger portions are moderate. The salt does much of the portioning for you, since a dish seasoned well past a tablespoon becomes too salty to eat, 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 very little itself at a tablespoon, so the total load of a meal comes from everything around it: the noodles, the vegetables, the mushrooms or legumes that bring GOS and mannitol of their own. 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 about 1 tablespoon (20mL) 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 low at about 1 tablespoon (20mL), as a simple ferment of fish and salt. Larger portions are moderate and much larger portions are high.

how much fish sauce can i use

About 1 tablespoon (20mL) is low, which covers what most recipes call for. Larger portions are moderate, and 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 at about 1 tablespoon (20mL) 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.