Ornithine and arginine, two of the amino acids involved in the release of human growth hormone, are a dynamic duo and among the most popular amino acid supplements today, mainly because they can help you slim down and shape up while you sleep (which is when GH is secreted).  While some hormones encourage the body to store fat, growth hormone acts as a mobilizer of fat, helping you to not only look trimmer but have more energy as well.

Ornithine stimulates insulin secretion and helps insulin work as an anabolic (muscle building) hormone, which has increased its use among bodybuilders.  Taking extra ornithine will help increase the levels of arginine in your body.  (Actually, arginine is constructed from ornithine; ornithine is released from arginine in a continuing cyclic process.)

As a supplement, ornithine works best when taken at the same time and in the same manner as arginine (on an empty stomach, with juice or water, no protein).