Effects of age, sex, and clinical conditions on adipose tissue cellularity in man

Methods for measurements of fat cell size in man are now available. Total fat cell number is more difficult to measure, and the numbers reported should probably so far be regarded as estimates of fat-containing fat cells. The first years of life seem to be critical for adipose tissue development in man. Nonobese adult women probably have more fat cells than men. Fat cell size increases with age.Obese children and adults show increases in both fat cell size and number. Division of obese subjects into different subgroups according to adipose tissue cellularity must take into consideration the age and sex variations in the nonobese population. Attempts to such subdivision seem to give one group with an increased number of fat cells, early debut of obesity, and increased body cell mass. These patients are difficult to treat successfully by conventional methods. Adult onset obesity seems to be characterized by enlarged fat cells.All data presently available are transsectional and do not allow any definite conclusions about possible fat cell division. Thus, there might well be adult obese subjects who, like certain genetically obese rodents, have fat cells which multiply during an abnormally long period of life.Fat cell size has been found to correlate with plasma insulin and triglyceride concentrations. Patients with endogenous hypertriglyceridemia and possibly adult onset diabetes mellitus before debut of the diabetes have enlarged fat cells, while patients with juvenile, insulin-requiring diabetes mellitus have small fat cells.Thus, the subgrouping of obesity according to the cellularity of adipose tissue has given associations with clinical observations such as age at debut of obesity, disturbances of carbohydrate and lipid metabolism, and with prognosis for treatment. These relationships seem to justify the adipose cellularity measurements as they are now performed, although only a fairly rough estimate of the total cell number is obtained.