Fish sauce and soy sauce are both classic Asian condiments with long histories. They are essential for a large number of savory dishes and can enhance many Western favorites as well. While there is a significant overlap in how they are used, they have very different properties. In this SPICEography Showdown, we look at how fish sauce and soy sauce compare to each other.
How does fish sauce differ from soy sauce?
The first difference has to do with the main ingredients in both. While both fish sauce and soy sauce are heavily reliant on salt for their respective flavor profiles, each has a distinctive set of other flavors that is accentuated by the salt. Fish sauce is made from fermented fish; soy sauce is made from fermented soybeans and wheat.
Fish Sauce 
Soy Sauce
One of the big differences between fish sauce and soy sauce has to do with animal proteins. Because it is made from fish, soy sauce is not suitable for vegans; soy sauce contains no animal products.
As you might expect from a sauce made with aged anchovies, fish sauce has a pungent fishy smell. Soy sauce does not have this smell.
Fish sauce has a translucent brown color similar to the color of apple juice while soy sauce is much darker.
If your recipe calls for one, can you use the other?
Fish sauce can work as a substitute for soy sauce in some applications. Note that it won’t be suitable for people who have seafood allergies or for vegans. It will provide the saltiness and umami complexity that you want from soy sauce but with a good deal of fishiness alongside it.
The way to avoid the fishiness is to use only a small amount of it or offset it with some lime or lemon juice. Keep in mind that while lime juice will offset most of the fishiness, a little will always remain. When using fish sauce in place of soy sauce, start with a fraction of the amount required in the recipe and then increase to taste.
You can use soy sauce in place of fish sauce and get much of the same umami kick. It is ideal for people with the aforementioned seafood allergies or who are vegan, but not for people who are sensitive to gluten.
The dark color of soy sauce will also have a dramatic effect on the appearance of most dishes that require fish sauce. If you want to make your soy sauce a little more fishy-tasting, finely grind an anchovy and add it to the sauce.
When should you use fish sauce and when should you use soy sauce?
Use fish sauce in South Asian dishes that will benefit from the umami kick. It is essential for the Thai dipping sauce known as prik nam pla where it is combined with lime juice and hot chiles. You can use it to add enhance the umami profile of Western dishes as well. Use it in marinades for chicken, pork or beef. Add it to salad dressings and soups.
Soy sauce is equally versatile. You can use it as a dipping condiment or use it in marinades to enhance both the color and umami notes in a dish. Use it for fried rice, in your noodles or even as an addition to barbecue sauce.