For a long time, yeast was touted as a kind of super-food. As a living organism, the claims boasted, it could help increase vitality, eliminate fatigue and cure any number of ailments. After all, look what it's done for bread. Unfortunately, none of the claims were demonstrated (except for the bread part).
Nonetheless, yeast became a popular nutritional supplement long before the current glut of such products. People would consume yeast, along with cod liver oil, as a sort of "multivitamin" supplement. As is the case with most supplements, the hype far outstripped reality. Yeast--in all of its thousands of varieties--is nothing more than a one-celled fungus.
We see it most often as baker's or brewer's yeast. The former is what we use for making bread, and it is quite nutritious. One tablespoon of the dried yeast has just 23 calories and 3 grams of protein but surprisingly high levels of iron, phosphorus and B vitamins. However, when taken as a supplement, live baker's yeast can cause intestinal gas. And if it isn't rendered "inactive" by cooking (as it would be in baking bread), it can actually rob your body of thiamine. (This seems to happen because the yeast cells gobble up most of the thiamine for themselves and don't release it back into the bloodstream.) Yeast supplements normally sold in health-food stores are inactive and non-fermenting.
Brewer's yeast, which is left over in the process of making beer, is an inactive form of yeast that has already been killed off by heating. By itself, it is almost too bitter to eat and must undergo a special "de-bittering" process to make it palatable. Supplements labeled "nutritional" or "primary" yeast are much easier to get down. They vary in nutrients, depending on whether they've been fortified with vitamins; a tablespoon of plain, unfortified brewer's yeast has 28 calories, 3 to 4 grams of protein, the entire recommended daily allowance for thiamine, 25% of the RDA for riboflavin and about 20% of the RDA for niacin. It is also rich in chromium.
Some supplemental yeast varieties are "super-fortified"; these contain five to 10 times the recommended daily allowance for certain vitamins, as well as digestive enzymes--and other substances that haven't been shown to have any useful purpose.
One specific drawback of yeast supplements is that they contain a substance called purine, which may actually be responsible for the development of gout in people at high risk for that painful condition.
It's hard to imagine why anybody would need yeast supplements. The vitamins they contain are readily available in meat, poultry, grains, fruits and vegetables. Most people already consume more than enough protein. And yeast supplements contribute nothing to fiber intake or the sheer pleasure of eating real food. If you feel that your diet needs supplementation, a multivitamin is a more reliable source of nutrients.
So forget the myth of yeast's magic.
At the other extreme, though, are individuals who believe we should avoid yeast. They maintain that excess yeast (and sugar) in the diet causes an overgrowth of the fungus Candida albicans, which can lead to suppression of the immune system and a predisposition to such disorders as depression, hyperactivity, upset stomach, premenstrual syndrome, rheumatoid arthritis, cancer, multiple sclerosis and even AIDS. Their claims haven't been borne out by good scientific studies.
Candida, in fact, is a widespread human and animal yeast that lives primarily in the mouth, throat, intestines and vagina. Vaginal yeast infections are not uncommon in women; more widespread infection is also frequently seen in people who are already extremely ill or on long-term antibiotic therapy.
However, for most individuals, even a serious overgrowth of Candida is not a problem that requires any particular treatment or lifestyle modification. Nonetheless, there are those who say that the "prescription" is the elimination of all sugar and yeast, as well as processed (even frozen) foods. Of course, they would also suggest that you install air filters to create "safe rooms," give up cosmetics and other products that contain petrochemicals, and take anti-fungal drugs. Unfortunately, such therapies may be a waste of time, energy and hope. To make matters worse, some anti-fungal drugs can have serious negative side effects.
So, fellow consumers, save your money. Yeast is neither all good nor all bad. It is certainly not a wonder drug, but it's also not something you need to avoid.
If you do buy yeast, buy the active variety, and incorporate it into a loaf or two of homemade, whole-grain bread. The nutritional value will be much greater, and the kneading process is a sure-fire stress reducer.
Dr. Sheldon Margen is a professor of public health at UC Berkeley; Dale A. Ogar is managing editor of the UC Berkeley Wellness Letter. Send questions to Dale Ogar, School of Public Health, UC Berkeley, Berkeley, CA 94720-7360, or e-mail to firstname.lastname@example.org. Eating Smart appears the second and fourth Mondays of the month.