Brewer's yeast is the dried cells of the fungus Saccharomyces cerevisiae. Originally obtained as a by-product of beer making, and now cultured specifically for use as a dietary supplement, brewer's yeast is a rich source of the trace minerals chromium, selenium, and copper and is very high in protein (over 50 percent protein by weight), with 18 different amino acids. Brewer's yeast is also a good source of many B-complex vitamins, most notably thiamin, riboflavin, niacin, vitamin B-6 (pyridoxine), and folic acid. While traditional brewer's yeast has a strong bitter taste, "debittered" yeast is also available.
The dosage for brewer's yeast approved by Commission E is 6 grams per day. Brewer's yeast appears to be well tolerated at this dosage level; however, side effects such as migraine-like headaches have been reported on some sensitive individuals