Various aspects of obesity factors
Obesity has been one of the major health concerns for many years. There are many ancient documents and references regarding being obese or thin. According to the Lingshu (靈樞), published in Chin-Han(秦漢) era, the oldest classic of oriental medicine, people with different physical types (i.e. being obese or thin) need different applications of acupuncture.

“Fat people have large shoulders and armholes with dark and tough skins..........This type of people should be applied with deep and prolonged acupuncture..........On the contrary; thin people have haggard faces and bodies with thin skins............ These people need shallow and fast acupuncture.”

For thousands of years, people knew differences between what is normal and abnormal (i.e. fat or thin). The matter of being fat or thin has been always the main interest in medical history.

Modern nutritionists suggest various theories for explaining causes of obesity.  Among the theories, the most compelling one is the imbalance between energy intake by metabolic factors and energy consumption. This means obesity is the result of excessive accumulation of body fat or energy, which is caused by too much food and/or too little exercise.  However, the theory does not give a complete answer for the reason of being obese, because there are certain people who have a higher risk of becoming obese than other people despite eating the same amount of food.

The other theories for explaining obesity are environmental theory and genetic theory.  The environmental theory suggests various environmental inducements in relation with life style habits, cultural or socioeconomic status can cause obesity.  For example, modern environmental factors such as high calorie foods and sedentary life style can induce obesity. However, it is unclear whether the environmental inducements are the only causes of obesity without excluding genetic factors.

The latter theory, genetic theory, explains obesity is genetically inherited, which is supported by a number of research results. In this theory, people who have family history of obesity may have higher risk of being obese than other people. For instance, if both parents have normal weights, the obesity rate of their children is only 10%.  However, if one of the parents is obese, the rate increases to 50% and if both parents are obese, the rate increases to 80%. This result suggests that the genetic factors cannot be disregarded for explaining obesity.

Set Point (Fixed Point) Theory
The most promising theory for explaining obesity factor is the “Set Point Theory”.  This theory seems to use similar approach with those of constitutional medical theory for explaining obesity factors.

According to the Set Point Theory, which was published by Schwartz and Seeley, people are born with certain set (fixed) range of weights like skin, eye or hair colors or heights. That is, body shapes (i.e. fat, thin or normal) and body weights are genetically predisposed.  We cannot choose to be fat or thin!  Every person is born with his/her own range of weight, which is called set point or fixed point. For example, some people are born with height of 170cm and weight of 70-90 kg, while others are born with 160cm and 50-70 kg. The set range of weight can be changed by dieting during lifetime, but it is very difficult to change the set point, because of human body’s tendency for homeostasis to keep the original weight range.

People who has experiences of dieting know how hard to lose and maintain their weights. When people start diet, they lose several pounds within a few weeks. However, after then, although they restrict their food intakes by dieting, some people regain their original weight or even more by yoyo effects. The result is caused by human body’s tendency to keep and restore its set point weight despite our painstaking efforts to lose weight.

If we decrease food intakes to change our set point weights, not only our body weights decrease below the set point, but also our metabolic activity decreases and thus our body starts to conserve energy. In this case, decreased body activity with hunger results in body movement toward losing fewer calories such as more sleep or loss of body temperature. For example, people with loss of appetite due to dieting are more sensitive to the cold or suffer from disorders of menstruation.

On the other hand, when the body weight increases above the set point, the metabolic activity increases. With increased metabolic activity, our body burns the excessive calorie intakes by increasing body temperature. Accordingly, our body weight is affected by various body functions such as body temperature, blood pressure and maintains its set point weight by our body adaptation mechanism.

The Set Point Theory suggests the followings: Some people born without obesity factor cannot be obese, even though they are exposed to obesity inducing environments.  However, no matter how hard they may try, some people are predisposed to be obese, because they are born with obesity factor.

Constitutional medical viewpoint of obesity factors
The above Set Point Theory has a similar viewpoint with constitutional medicine, which describes “Obesity is determined by body constitution.” Although the Set Point Theory suggests a proper approach for explaining obesity without including inducing or external factor, the theory does not give a sufficient answer to physiological and/or inherited factors, which determines the body type of obesity.
Like the Set Point Theory, the constitutional medical theory takes the inborn body shape theory. However, the constitutional medical theory focuses on zhang-fu [the five viscera (liver, lungs, heart, kidney, and spleen) and the six entrails (of gall bladder, stomach, small and large intestines, the paunch, the bladder and the bowels)] rather than body shape: our body shape is determined by our inborn organ structure. That is, each person is born with his/her unique organ structure, which decides his/her constitution. The imbalance between functional increase and decrease of relevant zhang-fu is the main reason of obesity. Therefore, anyone who is exposed to obesity factors cannot be fat. Only some people who has certain internal organ related to obesity can become obese. In other words, anyone born with obesity-free organ may not be obese, even though he or she is exposed to obesity factors. Because each person has different capacity for coping with the same causes depending on his/her constitution. In this viewpoint, “Obesity is a phenomenon of body constitution.”

(Table1) The Organ Structure of Eigh Constitutions

An obesity-prone type is the person who is born with strong pancreas, precisely pancreas yang, which is in charge of digestive and absorptive functions. As shown in table 1, a Yol-Soyangin, who is born with the strongest pancreas, is the most obesity-prone type or constitution, and who is followed by a Yol-Taeumin, the person with the second strongest pancreas.

In addition, Table 1 provides that a Han-Soyangin also has the organ structure of a strong pancreas (from strongest to weakest: pancreas > liver > lung > kidney). Unlike other obesity-prone types, the Han-Soyangin can become overweight, but not obese. It is because the physical constitution of a Yol-soyangin has excessive “pancreas yang”, while that of a Han-Soyangin is deficient in “kidney yang”. Besides, the strong pancreas of a Han-Soyangin does not imply excessiveness of “pancreas yang”, but “pancreas yin”. A Yol-Taeyangin also has the organ structure of the second strongest pancreas. As described in the case of the Han-Soyangin, a