Nutritional yeast (also known as nooch) is a deactivated yeast, often a strain of Saccharomyces cerevisiae, that is sold commercially as a food product. It is sold in the form of yellow flakes, granules, or powder and can be found in the bulk aisle of most natural food stores. It is popular with vegans and vegetarians and may be used as an ingredient in recipes or as a condiment.

It is a significant source of some B-complex vitamins and contains trace amounts of several other vitamins and minerals. Sometimes nutritional yeast is fortified with vitamin B₁₂, another reason it is popular with vegans.

Nutritional yeast has a strong flavor that is described as nutty or cheesy, which makes it popular as an ingredient in cheese substitutes. It is often used by vegans in place of cheese in, for example, mashed and fried potatoes or scrambled tofu, or as a topping for popcorn.

In Australia, it is sometimes sold as "savoury yeast flakes". In New Zealand, it has long been known as Brufax. Though "nutritional yeast" usually refers to commercial products, inadequately fed prisoners of war have used "home-grown" yeast to prevent vitamin deficiency. Nutritional yeast is a whole-cell inactive yeast that contains both soluble and insoluble parts, which is different from yeast extract. Yeast extract is made by centrifuging inactive nutritional yeast and concentrating the water soluble yeast cell proteins which are rich in glutamic acid, nucleotides, and peptides, the flavor compounds responsible for umami taste.