Classification of obesity with respect to morbidity.

Obesity is defined as an excess accumulation of adipose tissue in the body. Since its etiology and pathogenesis are quite heterogenous, classification of disease types by specific purposes is essential for proper clinical management. Although classification by the etiology given in Table I is useful for diagnosing the primary disease inducing obesity, it would be more meaningful to classify simple obesity into subgroups and determine pathological features of each disease type, since simple obesities without specific identifiable cause are much more often encountered in daily medical care. From this viewpoint, classification by morphological types of fat cells or by sites of adipose tissue accumulation has been carried out as shown in Parts II and III of Table I, and features of each disease type have been reviewed. This paper explains the above in detail, and describes a method of classification that incorporates the concept of visceral fats in comparison with conventional methods. As for the accumulation sites, visceral fat can be analyzed by a newly developed method. This is to classify obesities by cellularity of the adipose tissue biopsied, i.e., by the size and number of fat cells (1). The following classifications are employed because metabolic disorders accompanying obesity are related to the size of fat cells and because of the relationship between the proliferative capacity of fat cells and the onset of obesity. Hyperplastic Type. Fat cells are normal in size, but are increased in number. Fat cells are said to actively proliferate from the embryonal period (the last trimester of pregnancy) to 1 year after birth, and again during puberty. This type is, therefore, often seen among obese people with onset in youth. Since fat cells are not large, metabolic disorders rarely occur. The treatment for weight reduction is not so effective.