Sorting Out Yeast: Nutritional and Brewer's
'Nutritional yeast, commonly known as nooch, is popular among people following a vegetarian or vegan diet. It provides a non-animal source of protein that contains all nine essential amino acids (the ones you can obtain only via your diet, typically from animal protein sources).
Nutritional yeast is also widely regarded as a good source of B vitamins, including vitamin B12, another nutrient typically only found in animal foods. Perhaps best of all, nutritional yeast has a nutty, cheese-like flavor that can be used as a cheese substitute in recipes.'