Brewer's yeast, which is often called nutritional yeast, was originally a by-product of the brewing of beer. While still used for brewing, it is also now produced for its nutritional value. Nutritional yeast is not exactly the same as brewer's yeast. Brewer's yeast was originally used as a nutritional supplement, then other yeasts were made available for this purpose. Brewer's yeast differs from live baker's yeast in that its live yeast cells have been destroyed, leaving the nutrients behind. Live yeast cells can actually deplete the body of B vitamins and other nutrients.

Nutritional yeast contains high levels of many important nutrients, including all of the B vitamins (except for B₁₂), 16 out of 20 amino acids, and 14 different minerals. The amino acids in yeast are protein components which help the body repair tissue and fight disease. Brewer's yeast has a high protein content, with 1 tbsp. providing 4.6 g, making it a rich source of protein for vegetarians. It is also high in phosphorus.

Because yeast is such a rich source of the B vitamin family, it enhances the roles these vitamins play in the body. The B-complex vitamins support and optimize carbohydrate, fat, and protein metabolism. They also support the nervous system and maintain tonicity in gastrointestinal muscles. Different B vitamins play different roles, particularly in their support of the nervous system. They relieve stress, depression, irritability, and fatigue, and also help protect against aging. When under the pressures of stress or infection, the body needs higher supplies of these important vitamins. The body does not store excess B vitamins, so they must be continually replenished. B vitamins can also help deter morning sickness.

Biotin, one of the B vitamins that brewer's yeast supplies, has been shown to strengthen brittle nails and improve the health of hair. It also improves the metabolism of scalp oils, which make it an important treatment for seborrheic dermatitis, a condition seen most often in infants ("cradle cap") and the elderly. Biotin is also used to treat diabetes, since it enhances insulin sensitivity, increases glucokinase activity, and is helpful for treating diabetic neuropathy.

Brewer's yeast is also an important source of chromium. There is no official RDA for chromium, but the U.S. FDA recommends 120 mcg daily. However, 90% of Americans are deficient in this important mineral. Chromium has the ability to significantly lower low density lipoprotein (LDL) levels in the blood and raise high density lipoprotein (HDL) levels. Studies have shown that cardiac patients can have 40% lower blood levels of chromium than those without coronary artery disease. Some research has suggested that brewer's yeast also contains other hypocholesterolemic factors beyond its rich chromium content.

Chromium is also an important supplement for those with Type II (adult onset) diabetes. It can significantly lower blood glucose levels by aiding transmission of insulin into the cells. Researchers have been able to lower some glucose levels in diabetics to almost normal levels with daily chromium doses of 1,000 mcg. Chromium supplementation should be considered as an adjunct to started medications.

Even if blood glucose levels are normal, skin glucose tolerance appears to be impaired in cases of acne. Several studies have tested the use of chromium for acne treatment, with good results. Chromium's ability to increase the effectiveness of insulin's activity in the body has also led to its use as a weight loss aid. Chromium can be difficult for the body to absorb, but brewer's yeast is one of most absorbable ways to take it.

Chromium, thiamine, nicotinic acid, riboflavine, pyridoxine, pantothenic acid, biotin, folic acid, cyanocobalamin, aminobenzoic acid, and inositol.

Brewer's yeast comes in powder, flake, tablet, and liquid form.

• As a source of chromium: to reduce blood sugar levels in Type II diabetics, to lower blood cholesterol levels, to aid in weight loss, and to aid in the treatment of acne
• As a source of B vitamins: to relieve stress, depression, irritability, and fatigue
• As a source of biotin: to strengthen hair and nails and treat seborrheic dermatitis and diabetes

Can be taken in juice or water; 4 tbsp. per day are recommended. If the body's diet is low in B vitamins, this amount may cause gas. It is best to begin with 1 tsp. in a glass of juice and work slowly up to 4 tbsp. Nutritional yeast may be taken as a source of chromium to assist weight loss and treat impaired glucose tolerance, or of biotin to promote strong nails and healthy hair and treat cradle cap, diabetes, and diabetic neuropathy.

Brewer's yeast has no known side effects.

Be cautious with yeast products if you have an overgrowth of intestinal yeast (Candida albicans or rhodotorula yeast). People with osteoporosis should avoid yeast because of its high levels of phosphorus. If taking a yeast supplement, also take extra calcium.

Brewer's yeast contains a significant amount of tyramine, which should be avoided while on monoamine oxidase inhibitor (MAOI) therapy (Utermohlen 1999). MAOI medications include phenelzine, tranylcypromine, pargyline, selegiline, and isocarboxazid. In addition, brewer's yeast may interact with meperdine, a narcotic analgesic. The dangerous interaction between brewer's yeast and these medications could lead to "hypertensive crisis," a rapid and severe increase in blood pressure that is characterized by nausea, vomiting, headache, and palpitations. This reaction may result in a myocardial infarction or stroke.

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