Human growth is an invisible but intense process, an intricate and little understood web of genes, hormones and other variables. Genetics aside, growth hormone may be the single biggest player. Between 10 and 30 times a day, your hypothalamus sends a growth hormoneâ€releasing hormone to the garbanzo-bean-size pituitary gland at the base of your brain. Each time the pituitary gland receives a signal, it spits out a small amount of growth hormone. Although scientists think a small percentage of hGH travels to your bones, a majority of the hormone latches onto binding proteins, which carry it to receptors in your liver cells. This triggers the secretion of insulin-like growth factor-1 (IGF-1), a protein that promotes bone growth in children and teenagers until their growth plates, areas at the ends of the bones, fuse, at around age 17 for boys or 15 for girls. After that, growth hormone continues to regulate the metabolic system, burning fat and building muscle, but we produce exponentially less hGH each decade after puberty. Thus, the teenager who can routinely "supersize it" without consequence ages into the 30-year-old whose beer and burgers go straight to his gut.