Soy sauce is composed of five basic tastes: sweet, sour, salty, bitter, and umami. For a similar liquid that lives up to soy sauce’s umami flavor, use Worcestershire sauce.
Much like soy sauce, Worcestershire is a fermented condiment, but it's made from vinegar and molasses and flavored with anchovies, tamarind, and aromatics.
It has less sodium but still contains the rich umami taste that soy sauce has. Worcestershire sauce can be used in equal proportions when used for flavor rather than saltiness.
Vegans can opt for balsamic vinegar instead of Worcestershire sauce. Miso paste is another vegan soy sauce substitute that contains similar ingredients and is also fermented.