The adipocyte-number hypothesis.

The adipocyte-number hypothesis was derived from experimental studies of rats. It states the number of adipocytes (fat cells) is fixed early in life and predestines an individual to be lean or obese depending on changes in the number of adipocytes. However, the present methods for estimating adipocyte number are based on the estimation of total body fat and of adipocyte size. While total body fat can be measured reliably, little is known of the validity of these estimates. the measurement of adipocyte size is reliable if care is taken that cells are not damaged during the application of those methods in which cells are isolated. Nevertheless, these methods are probably preferable to those based on the measurement of intact tissues; human errors are more likely with the latter. The major problem with the measurement of adipocyte size is the unrepresentative nature of the specimen examined and the fact that adipocytes that are devoid of fat are not included in the count. There is disagreement as to whether the rapid increases in total body fat during infancy are due mainly to increases in adipocyte number or in adipocyte size. Furthermore, data from animal experiments indicate that the number of adipocytes may not be fixed during adult life. Age-to-age correlations show almost 0 correlations between measures of obesity before 6 years and the same measures at 16 years, but these correlations increase rapidly after 6 years. Serial data show no more than a slight tendency for obese infants to become obese adults. These findings do not support the adipocyte-number hypothesis.