In China, the concept of medicinal foods, or ordinary food that can be used to treat illness, is not new. In his book Eating Your Way to Health, Cai Jingfeng explains that food and medicine had a common origin, since during prehistoric times, man must have eaten plants and fruits that had therapeutic effect on the body as well as providing nutrition.

The legendary Shen Nong, who is credited with introducing agriculture to China, was said to have tasted all the plants and waters to know which was poisonous or beneficial. In the course of his experiments, he was poisoned at least seventy times.

As early as the Warring States period, the effect that food could have on health has been chronicled in Chinese writing. Cai cites a quotation from the Book of Han Fei (280-233 BC) that mentioned how people got sick after eating food that had an adverse affect on the body. In the 11th century, a king named Tang from the Shang dynasty was reputed to have a cook named Yi Yin, who cooked soups for the king when he was ill. The soups were credited with bringing the king back to health.

In Traditional Chinese Medicine, according to Cai, the body is considered healthy when it is in a harmonious state. Traditional Chinese Medicine uses many common food as medicine, taking into account both the nature and flavor of food to achieve this. Food can be cool, cold, warm or hot. It can be salty, sour, sweet, bitter and pungent. In Traditional Chinese Medicine, disease is cured by applying the opposite nature and flavor to that of the illness.

Illnesses with symptoms such as high fever, thirst, headache, deep-coloured urine and yellow fur on the tongue surface are said to be of a hot and excessive nature, Cai explains. Diseases with symptoms such as cold extremities, chills and shortness of breath are of a cold and deficient nature. In severe cases of hot illnesses, cold remedies should be used; in milder ones, cool remedies. Cold diseases, then, are treated with hot or warm remedies.

Here's a brief list of medicinal foods and what they are used for:
 
Neutral food
black beans - to blacken hair and to ease post-partum pain
soybeans - for anemia, asthma and to promote lactation
carrots - to prevent night blindness and promotes digestive function
chrysanthemum - for fever, also relieves dizziness

Cold food
banana - for constipation and hemorrhoids
freshwater clams - for fever and detoxifying
cucumber - for fever, sore throat and red eyes
pear - for thirst and constipation

Cool food
bitter almond - for chronic bronchitis
celery - for hypertension
duck - hypertension with dizziness
watermelon - for sore throat and to relieve summer heat

Hot food
chili - to stimulate the appetite
black and white pepper - warms up the body
clove - warms the spleen and stomach, stops vomiting

Warm food
aniseed - relieves intestinal spasm
beef - for the tendons and bones
garlic - for dysentery
coriander - for skin rashes