Five is a key number in traditional Chinese philosophy and traditional Chinese medicine, which are related in a comprehensive system emphasizing harmony and balance.

The Theory of Five Elements (wu xing) is a cohesive description of all material things and movements in the universe and in the human body, which corresponds to it. Together with complementary yin ("cold") and yang ("hot") energies, the five elements form the basis of traditional healing.

The universe is comprised of five basic elements: metal, wood, water, fire and earth. These also can be interpreted as forces. The human body is comprised of five major organs: heart, liver, spleen, lung and kidney. The year has five seasons (rather than four) in TCM: spring, summer, long summer (late summer), autumn and winter. Further, there are five corresponding musical notes, five flavors, five colors, five directions and five sense organs.

All are related in a tightly knit metaphysical system.

The Theory of Five Elements, which is coordinated with all the other "fives" (music, color, flavor and so on) is a basic theory in traditional Chinese medicine. It describes and explains the relations among different organs of the body and how they affect function and physiology of the whole. The theory is also used to explain the relationship between the human body and the universe so that one can follow the larger rhythms of nature and stay healthy and in balance; or take rebalancing medication as needed.

Wu xing is the way ancient Chinese people observed and explained the changes and relations in the universe, according to Professor Qian Hai of the Shanghai University of Traditional Chinese Medicine. Wu (five) refers to the five basic elements - metal, wood, water, fire and water; while xing (move) indicates movements and changes.

The five elements are also influenced by yin-yang energies and their own interactions, thus resulting in changes in the universe.

"It is not that everything is really composed of the exact materials of five elements, but that the characteristics of the five can help describe almost everything that you can name," Qian says.

For example, wood represents the ability of growth, extension and flexibility. Fire indicates heat, warmness and an ascending power. Earth, as the mother of all living things indicates nourishing, changing, bearing life. Metal indicates firmness, strength, restraint and cleaning. And water describes everything that is cool, nourishing, descending, and that stores or conserves.

Similarly, as the sun rises in the east and as wood grows, the direction east belongs to "wood." Summer belongs to "fire." The spleen (digestive system) is responsible for digesting and transferring nutrition to the organs and plays a role similar to that of earth; thus it belongs to "earth." The kidneys (urinary and reproductive systems) that govern urination and storage of "essential energy" belong to "water."

These ideas also govern musical notes, colors, flavors, senses and directions.

With careful observation of the natural world, ancient Chinese discovered simple rules about the five actions of the five elements, which are frequently used today. They are basically the rules of "generation" and "restriction."

Wood generates fire as it can be used as fuel; fire generates earth as it burns things into ashes; earth generates metal as metals are always found in the earth; metal generates water as water vapor (condensation) is often found on metal surfaces; water generates wood and wood (trees, plants) grow with water.

On the other hand, wood restricts earth as it can absorb nutrition from the earth; earth restricts water as it can absorb water; water restricts fire as it can extinguish it; fire restricts metal as it melt it; metal restricts wood as a metal ax or saw and fell wood.

It is not that everything is really composed of the exact materials of five elements, but that the characteristics of the five can help describe almost everything that you can name.

"Though the five elements seem to be very different characteristics,they are closely related with each other. Change in one element can directly lead to a broken balance in others," says professor Qian.For example,weakened earth will lead to overly active wood in the universe, and thus break the balance.

And as for human body,which is also composed of the five basic elements and coordinates with the universe, it responses quickly to the changes of elements inside or outside the body.That may provide guidance about adjusting habits in accordance with changes in the universe, to maintain internal balance.

Usually, in spring - the season of wood when things grow- it is advised to give the liver more nutrition that benefits the liver,namely foods in the wood category, such as green vegetables. Sour foods should be avoided,lest they cause too much liver energy that restricts the spleen(digestive system) related to earth.

In spring, music of the tone shang(Re) of metal or tone yu(La) of water are more suitable for the season, since metal can restrict wood from becoming overly active, while water can nourish wood and make it soft and obedient.

In summer it's the season to nourish the heart with red foods that are not too bitter;in late summer, yellow,somewhat sweet foods are good for the spleen; in autumn the lungs need white nourishing foods;in winter,it's time to nourish the kidneys with black foods.

And hidden disorders within the body are sometimes more easily detected by observing coordinated things of the same category.

Some spas in Shanghai adopt TCM and give guests a short questionnaire before treatment, to detemine which organ needs special care. Qusetions often refer to the current weather,preferred color,taste preference and recent mood.

According to Daphne Li, manager of Chuan Spa at The Langham,Xintiandi,Shanghai hotel, more guests answers correlate with the "metal" category in autumn,which indicates need to nourish the lungs. After big holidays when there is lots of eating,customers answers generally fall into the "earth" category,which means their digestive system needs attention.