HGH (Human Growth Hormone) stimulates growth in most body tissues, primarily due to increases in cell number rather than size. This includes skeletal muscle tissue. The transport of amino acids is also increased, as is the rate of protein synthesis. All of these effect are actually mediated by IGF-1 (insulin-like growth factor), a highly anabolic hormone produced in the liver and other tissues in response to growth hormone. A shift is seen where fats become a more primary source of fuel, further enhancing body fat loss.