Stem cells hold a unique role in human physiology being as yet undifferentiated into any specific mature cell type. Depending on the signals and environmental stimuli they receive, genetically identical stem cells may then differentiate into bone, heart, or even neurons. Hormone signals, such as insulin, may trigger stem cells to become adipocytes - fat cells, which may help explain why insulin-resistant people gain fat-mass so easily.

Currently, there are two methods by which one can undergo stem cell therapy. Exogenous therapies rely on stem cells harvested from either non-embryonic (adult somatic cells) or embryonic tissues with the latter being responsible for much of the controversy in early years. Once harvested, stem cells are grown in the lab, expanded in number, and conditioned before implantation back into the host. Stem cell clinics around the world offer treatment protocols for the regeneration of selected organs, such as heart or liver and for conditions such as diabetes and heart disease. The newest method is to expand your own stem cell population.