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 grown as a plant product 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, and 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 (proteins) in yeast help the body repair tissue and fight disease. Brewer's yeast has a very high protein content, with one 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 B vitamins, it enhances the roles these vitamins play in the body. The B-complex vitamins help your body metabolize carbohydrates, fats, and proteins. They also support the nervous system and help maintain the muscles used for digestion.

Different B vitamins play different roles, particularly in their support of the nervous system. They relieve stress, depression, irritability, and fatigue, and also help reduce some effects of aging. When under the pressures of stress or infection, the body needs greater supplies of B vitamins. The body does not store excess B vitamins, so they must be regularly consumed. B vitamins can also help relieve 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 is used to treat infant cradle cap. Biotin helps people with diabetes use insulin more efficiently and is useful for treating diabetic neuropathy.

Brewer's yeast is also an important source of chromium. The U.S. FDA recommends 120 mcg of chromium daily, but 90% of Americans are deficient in this important mineral. Chromium has the ability to significantly lower blood cholesterol levels.

Chromium is also an important supplement for those with Type II (adult onset) diabetes because it can significantly lower blood sugar levels. Without chromium, insulin is not able to work properly and blood sugar levels rise. Researchers have been able to lower some diabetic glucose levels to almost normal levels with daily chromium doses of 1,000 mcg.

Several studies have tested the use of chromium for the treatment of acne, with good results. Chromium's ability to increase the effectiveness of insulin's activity in the body has also led to its consideration as an aid to weight loss. Chromium can be difficult for the body to absorb, but is more easily absorbed when taken with brewer's yeast.

As a source of chromium, brewer's yeast can reduce blood sugar levels in people with type 2 diabetes, lower blood cholesterol levels, help with weight loss, and aid in the treatment of acne.

As a source of B vitamins, brewer's yeast can relieve stress, depression, irritability, and fatigue.

As a source of biotin, brewer's yeast can strengthen hair and nails, and treat cradle cap and diabetes.

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

You can dissolve brewer's yeast in juice or water. Four tbsp. per day are recommended. If your diet is low in B vitamins, this amount may cause gas, so it's best to begin with 1 tsp in a glass of juice and work slowly up to 4 tbsp.

There are no known side effects. However, you should avoid yeast products if you have frequent yeast infections. People who have osteoporosis should avoid yeast because of its high levels of phosphorus. If you take a yeast supplement, also take extra calcium.

Brewer's yeast contains a significant amount of tyramine, a substance that should be avoided if you are taking a monoamine oxidase inhibitor (MAOI), a type of antidepressant. Examples of MAOIs are phenelzine, tranylcypromine, pargyline, selegiline, and isocarboxazid. Selegiline is also used for the treatment of Parkinson's disease. Brewer's yeast may also interact with meperidine, a narcotic analgesic, used to treat intense pain. The dangerous interaction between brewer's yeast and these medications may lead to "hypertensive crisis," a rapid and severe increase in blood pressure that is characterized by nausea and vomiting, headache, and irregular heartbeat. This reaction may result in a heart attack or stroke.

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