Thank you Harry for the great post!
During ancient times, Chinese people developed their own theory for what constituted this world. They believed that everything in the world is composed of five basic elements, which are metal, wood, water, fire and soil. According to the idea of Yin Yang School, one of the oldest Chinese philosophies, the five elements make up things in the world through a series of cogenerations and conquests. The picture below illustrates the relationship between the five elements.
Ancient Chinese philosophers believed that the processes between five elements were catalysed by Yin and Yang, whose concept is illustrated below.
While Yang stands for things that are active, energetic and hot, Yin stands for darkness, and negativity. Although the Yin Yang School never dominated Chinese philosophies and its ideas can hardly be accepted in an evidence-based perspective, the two concepts, especially the concept of Yin and Yang, have been incorporated into almost every other Chinese philosophy, notably Confucianism and Daoism. Another important Chinese culture, the traditional Chinese medicine, relied heavily on the five elements and Yin and Yang to work.
Although different Chinese philosophies have had somehow different interpretations and applications of these two concepts, they do have share one common belief that the balance between Yin and Yang should be the optimal goal of everything in this world. For the purpose of this post, the influence of Yin-and-Yang idea has had on traditional Chinese food therapy will be introduced here.
If you asked my grandmother how the orange and the tangerine are different, she would not explain to you in a botanical perspective, but instead she would most likely tell you that tangerine is of Yin and orange is of Yang. As a lot of common food is directly used as medicine in traditional Chinese medicine, food therapy has thus played an important role in Chines culture.
The central idea of Chinese food therapy is the balance between Yin and Yang. For example, when I was young and had a fever, apart from taking medicine from the doctor, I would be asked by my grandmother to eat some watermelon, tangerine and avoid spicy food: she believed that there was too much Yang in my body and thus I needed to ingest food that could replenish my Yin and avoid food that could increase the Yang in my body. If Yin and Yang is considered as heat and cold, then the concept of the balance between Yin and Yang might indeed make sense intuitively. After all, a lot of people do put towels drenched in cold water on their forehead to make them feel better although they may never have heard of Yin and Yang. From the perspective of Chinese food therapy, this behaviour is exactly intended to rebalance Yin and Yang.
Usually, food that makes one feel energetic or hot is considered Yang food, such as pepper, beef and deep fried food; Yin food can usually make one feel cool and calm, such as watermelon, green tea (hot tea!) and honeydew.
It is impossible to comprehensively introduce the historic Chinese food therapy in a single blog post. Thus if you are interested in Chinese food therapy, I strongly encourage you to take a further look at it on the Internet or in related books you can find. I, however, do have a word of caution here: although it is fascinating, it is in no way a reliable way to cure your illness. So if you feel ill, never rely solely on food therapy but instead go and see a doctor!