Introduction
In this article we presents an overview of how testosterone is stimulated in the body, shows how calorie balance affects T production, and discusses how dietary protein intake affects circulating T levels.
The HPT Axis
An article on the effects of diet on hormones would be incomplete without a basic overview of the relationships between the organs and hormones of the axis. The term axis simply refers to the pathway in question. The glands of this pathway include the hypothalamus, pituitary, and testes. The sequence of events culminating with the production and/or release of T begins at the hypothalamus. Here specialized nerve cells release a hormone called gonadotropin-releasing hormone (GnRH). GnRH is a decapeptide (chain of ten amino acids) that travels by direct blood vessel connections to the anterior pituitary where it stimulates the release of luteinizing hormone (LH) (1). LH is then secreted into the blood where it attaches to receptors on the Leydig cells of the testes. This induces activity of an enzyme, P-450scc, referred to as the cholesterol-side-chain-cleavage enzyme (1). Through a series of five enzymatic steps, cholesterol is converted into T.
The body regulates the circulating blood levels of T via several mechanisms. Once in the blood, about 44% of T is bound to a protein called either sex-hormone-binding-globulin (SHBG) or testosterone-binding globulin (TeBG), to indicate the greater affinity for T over estradiol (E2, an estrogen). About 54% of T is bound by albumin and other proteins, leaving 2% to circulate