From the viewpoint of the pathogenesis of obesity it is of significance to know the relation between the abnormal metabolism observed during obesity and the morphological changes of fat cells.
Human subcutaneous adipose tissue obtained from the abdominal wall during surgery was fixed and isolated by incubation in a 2% osmium tetroxide solution, after which the number and size of the fat cells were ascertained. The total number of fat cells was determined by dividing the body fat by the lipid content of the fat cells. The size of the fat cells was determined by taking the average of the diameters of the fat cells measured under a microscope.
The results obtained were as follows:
On the basis of the size of fat cells, obesity may be classified into two types: obesity with hypertrophied fat cells, and obesity with normal size fat cells. The latter type occurs in children under ten years of age and is characterized by an increase in the number of fat cells. Hypertrophy of the fat cells was observed in most cases of medium or mild obesity.
Comparison of obesity characterized by hypertrophic fat cells and that with normal size fat cells revealed that the former type elicited a high insulin response and carbohydrate intolerance following oral glucose administration, and also showed a higher level of free fatty acids in the blood.
The causal relation between hypertrophy of fat cells and abnormal metabolism associated with high insulin response has not yet been clarified. However, it is thought that the high insulin response observed in the type of obesity with hypertrophic fat cells is a primary phenomenon and that the hypertrophy of the fat cells is due to the influence of insulin.