Traditional Chinese Medicine (TCM) views different types of foods as having specific impacts on health depending on their flavors. The primary categories in Traditional Chinese Medicine are bitter, pungent, salty, sour and sweet. Bitter foods, such as asparagus, bitter melon, wild cucumber, celery, coffee, grapefruit peel, kohlrabi, lettuce and vinegar are believed to promote health by reducing body heat and drying body fluids. Other categories have different health functions - for example, sweet foods are said to neutralize the toxic effects of other foods while sour foods such as lemon are used to treat diarrhea and excessive perspiration.
In TCM, bitter foods aren't necessarily viewed as better for overall health than foods with other flavors. For example, while bitter foods are seen as good for the heart and small intestine, sweet foods are said to be good for the stomach and spleen and the other flavors are beneficial for other internal organs. The idea is to include in your diet a balance of all five flavors.
Other cultures make use of bitter flavors to influence health as well. European herbalists are very fond of "bitters" to stimulate and tone the digestive system, and they rate gentian root as the best of them all. Several brands of alcoholic extracts of gentian root are available worldwide, most with other plants added for flavor. For example, Angostura bitters, a popular ingredient used in cocktails, is sold in most U.S. liquor stores and supermarkets. It is essentially a tincture of gentian root. For sluggish digestion, poor appetite, or flatulence, try taking a teaspoon of Angostura bitters before or after meals (experiment to see which works best for you). If you do not like it straight, try diluting it with sparkling water to make a (practically) nonalcoholic "cocktail." Gentian root is harmless and quite effective. Another well-known aperitif, Campari, is one of many bitter Italian drinks made from various herbs, spices, and fruit peels. You may be able to get a similar digestive effect, minus the alcohol, by beginning a meal with a salad of bitter greens such as curly endive, arugula, or dandelion greens flavored with lemon juice.
In Ayurvedic medicine, foods with bitter tastes are said to aid in weight loss and help control food cravings.
In the U.S. a bitter taste isn't always appreciated (with the exceptions of beer, coffee, and chocolate, and the latter two are often served heavily sweetened). We detect bitter taste via some 24 (receptors that enable us to respond to a wide variety of compounds), some of which are toxic (the ability to perceive a bitter taste probably evolved as protection against consuming poisons.) It's possible that our cultural disdain for bitter foods is linked to our immoderate consumption of sugar and sweets. I think certain bitter foods do offer distinct advantages, and I think it's a good idea to include more of them, judiciously, in the diet.
Andrew Weil, M.D.