DEAR DR. BLONZ: I drink lots of tea, mostly green and black (decaffeinated) with my meals. I am a vegetarian, and a nutritionist was concerned that I may be "losing" protein because the tannins in tea bind up the protein in my food. Is it true that tannins bind up proteins? Are there any teas that I would do better with? -- W.S., Madison, Wisconsin
DEAR W.S.: Tannins are naturally occurring plant substances that belong in the family known as the polyphenols. Certain tannins can indeed react and bind with proteins, but it should not be a concern since they tend to spread out their binding to other substances as well.
As teas go, black and oolong do contain relatively high levels of tannins, and green tea contains lesser amounts. To have a tea with low or no tannins, you will need to find one that is not made from leaves of the traditional tea plant (Camellia sinensis).
Protein can be affected by tannins, but a few cups of tea a day will not produce a worrisome protein-depleting effect. Most people -- including vegetarians -- eat more protein than their bodies require. (An interesting historical aside: Tannins derived from trees have long been used to react with the proteins in animal hides, and this process is integral to the "tanning" of hides into leather.)
Tannins can also affect the absorption of minerals such as iron and calcium, and this might be of greater concern. If you tend toward iron-deficiency anemia, it makes sense to avoid drinking a high-tannin tea with a key iron-rich meal. Calcium is less of a concern because there tends to be more of it in foods than there are tannins in tea.
For most people, an occasional loss of a few milligrams of an otherwise plentiful nutrient should not be a great concern. Tea has a number of healthful benefits, so enjoy.
DEAR DR. BLONZ: Can you explain the nutritional roles of zinc and copper? I heard it is not OK to have these at the same meal. -- U.A., San Francisco
DEAR U.A.: Zinc plays a role in many enzymes, including those involved in detoxification, sex-hormone production and wound healing. It is also involved in taste and smell. Copper helps in the formation of red blood cells, is essential for normal hair and skin, and is needed for normal respiration and the production of certain antioxidant enzymes.
Both are essential nutrients, and there is no problem taking recommended amounts at the same time. I think the source of your concern is based on the fact that too much zinc can deplete the level of copper in the body; likewise, if copper intake is excessive, the level of zinc can suffer. This antagonism only comes into play if there is an imbalance.
The take-home message, at least with zinc and copper, is that we shouldn't overdo it unless there is a medical reason to do so. At present, the Daily Value for zinc is 15 milligrams and the tolerable upper limit is 40 milligrams per day. For copper, the Daily Value is 2 milligrams and the tolerable upper limit is 10 milligrams per day. These figures are for adults 19 years of age or older. (For those not familiar with this term, "tolerable upper limit" is the highest level of intake that is likely not to pose any risk of adverse health effects in almost all individuals.)
Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.