China has a funny saying called "when you eat a grape, don't spit out the skin". The audience will probably see this as a joke: who eats grapes and doesn't spit out the skin? But from a food science perspective, this joke is not without sense. Grape skin (and especially skin of purple grapes) has a special nutrient, Resveratrol, that only very few other fruits have. This nutrient offers remarkable protection for the heart. In the fermentation process of French red wine, Resveratrol from the grape skins mixes in with the wine, so the wine loving French have the lowest rate of coronary heart diseases of all the other European countries.
Orange peel, the fruit with the largest production volume in China, has a similar function. It has citrus flavonoids, which are anti-cancer, lower blood sugar and have other health protection functions. An American food science researcher from the sixties found that the skin of watermelons has a natural amino acid matter called citrulline, which works as an aphrodisiac. Moreover, banana peel has a natural sleeping aid called 5-Hydroxytryptophan (5-HTP), which helps the brain with falling asleep. Banana peels also have a lot of potassium, which can help maintain a stable blood pressure.
There are many kinds of fruits that have beneficial peels. Like the tropical guava, that is produced in Taiwan and South-East Asian countries, whose skin is able to lower blood sugar. Its stones also have nutritional functions, almost as a medicine. According to nutritionists, a lot of fruit stones are inedible (such as apple seeds, pear seeds, cherry seeds, and apricot stones), because these stones have cyanophoric glycoside, which will change to hydrogen cyanic acid in the human digestive tract (a highly toxic chemical matter, that only needs a small amount to poison a person). According to food science experts, however, these stones are not only harmless, but are also a natural medicine. For example, the hard stones in the pineapple core have a natural digestive enzyme called bromelain, which can help the stomach to digest meat. Furthermore, the black seeds in lychees can actually reduce blood sugar. Boiling them to a soup will help to get high blood sugar back to normal.
