Other articles by Andrew Weil:

Ask Dr. Weil : Growing method doesn't determine nutrition value Ask Dr. Weil : Monitor toxins that body burden tests measure Ask Dr. Weil : Nasal-spray flu vaccine is safe for kids over 2 Supersweet, natural stevia appears to be safe Olive oil adulteration is a tough problem to solve Registered dietitians and certified nutritionists No reason to buy supplemental bovine colostrum No clear evidence on cell phone's long-term risks Soy eaten in whole, unrefined forms is preferable Chemical used for sterilizing almonds a concern

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Q I have a ginkgo biloba tree in my backyard. Naturally, I would like to take advantage of the famous ginkgo directly instead of shelling out money at a health-food store. But how do I use it?

A Ginkgo biloba is one of the most well-researched herbs in the world and is full of antioxidants and flavonoids. Ginkgo supports healthy circulation to both the brain and the extremities of the body. Studies suggest that this traditional Chinese remedy is capable of improving cognitive function as demonstrated by increased mental sharpness, better concentration and improved memory. If you try ginkgo for memory enhancement, you probably won't notice effects for six to eight weeks. Look for products standardized to 24 percent ginkgo flavone glycosides and 6 percent terpene lactones; the dose is 60 to 120 milligrams twice a day with food.

The tinctures and capsules of ginkgo biloba that you buy in stores contain extracts of leaves of the tree that is widely planted in cities and parks in North America. But I'm sorry to tell you that leaves you collect from these trees won't do you any good. In fact, they're more likely to irritate your stomach than to provide any of the positive effects you might expect. The extraction process used to make the popular herbal remedy removes the irritants and concentrates the beneficial components. However, if you have a female ginkgo tree, you can eat the nuts it produces. Ginkgo nuts are often used in Asian cooking. They have no medicinal properties but are tasty when cooked.

To get to the nut, you have to go through a pulpy layer of a persimmonlike fruit that is rather smelly (which is why female ginkgo trees and their nuts are not popular here). The nuts themselves resemble chickpeas and taste like chestnuts. To prepare them for eating, you first must peel or blanch them and then boil or roast them. In Asian cuisines, they are added to soups, stir-fry dishes and desserts. If your tree is not female (not producing fruit), you can buy dried or canned ginkgo nuts in most Asian groceries. One ounce provides 97 calories, 1 g fat, 0 cholesterol, 4 mg sodium and 0 fiber.

QI like to drink green tea, but it is staining my teeth brown. Do you have any suggestions?

ALike coffee and colas, tea can stain teeth, although it's not as big an offender as tobacco (smoked or chewed). Any food or drink capable of staining clothes or carpets — that includes fruit juices, red wine, blueberries, soy sauce and curry — can also stain teeth. Good-quality green tea that is really green in color is less likely to stain teeth than inferior grades of "green" tea that look brown when brewed. The best way to get rid of stains from any food or drink is with a professional teeth-cleaning, but, afterward, it's up to you to keep your teeth free of stains from foods and beverages.

I suggest rinsing your mouth with water after you drink tea (or coffee or colas). Be sure to brush your teeth twice a day with a whitening toothpaste and to floss daily (stains around the edges of your teeth occur when plaque accumulates at the gum line and absorbs color from food and drink).

You also may want to talk to your dentist about teeth-whitening options. Do-it-yourself kits are available for home use and can do a pretty good job. You're most likely to get the best results if your teeth are yellowish. Whitening won't "take" on teeth that have had bonding or tooth-colored fillings. The home-bleaching kits are generally considered safe, although you may notice some tooth sensitivity. My holistic dentist tells me that, over time, bleaching might break down the integrity of the teeth, leaving them more susceptible to future stains.

As an alternative to home whitening, your dentist can bleach your teeth in the office with professional products, sometimes augmented with laser light. This is more costly than the do-it-yourself route, but it usually can be completed in two to six sessions. These treatments can also create tooth sensitivity, but it usually decreases over time.