Only in extreme conditions can you add to this pool. For adults, we have no concrete figures, but the available evidence indicates that the number of cells that can become adipocytes is more or less constant unless you are exposed to extreme conditions. For example, if you develop morbid obesity, then you will start to generate more of these cells. The reverse, however, is not true. Starved adipocytes release all their stored triglycerides, but their numbers remain fairly constant.
Resume overeating and they resume storing fat.
Once committed, adipocytes apparently do not revert. The critical factor, said Hotamisligil, is what percentage of the adipocyte precursor pool crosses over. If all of them turn to adipocytes, than you will become obese. If none of them turns into adipocytes, then you will be abnormally thin or lipodystrophic. This transition between preadipocyte to adipocyte was known, but what was not known was what triggered the change.