Even in small amounts, nutritional yeast is a significant source of some B-complex vitamins.
Nutritional yeast (español: levadura nutricional) is a deactivated yeast, often a strain of Saccharomyces cerevisiae sold in the form of flakes or yellow powder. Its strong flavor is often described as nutty, cheesy, or creamy. Nutritional Yeast can be used as a flavor enhancer in cheese substitutes, mashed or fried potatoes, scrambled tofu, and popcorn. Some brands are fortified with additional B12. It has approximately 9 grams of protein in 2 tablespoons. It provides 9 amino acids that the human body cannot produce and 5% (unfortified) to 20% (fortified with B12) of recommended daily iron.
Sources: Wikipedia / healthline
WARNING: In large amounts, the high fiber content may cause digestive discomfort, and high niacin content can cause facial flushing. Some brands may contain tyramine, which can trigger migraines in certain individuals.