N-Acetyl-L-Tyrosine
A form of L-tyrosine touted for its high bioavailability.
L-Tyrosine
A conditionally-essential amino acid synthesized from L-phenylalanine. L-tyrosine is a precursor to the catecholamine neurotransmitters, l-dopa, dopamine, norepinephrine, and epinephrine – which are important contributors to mood and cognitive performance. It’s also a precursor to the thyroid hormone thyroxine (also known as T4).
In larger amounts, L-tyrosine has been shown to improve memory, psychomotor skills and cognitive performance under physical stress. L-tyrosine is frequently added to weight loss and pre-workout supplements to enhance alertness and (possibly) metabolism, although it is frequently underdosed.
May also be listed as 4-hydroxyphenylalanine.
For more information, see Paul’s review: “L-Tyrosine: Fat Burner & Anti-Depressant?”
Lutein
A dietary carotenoid that concentrates within the human lens and retina and protects against age-related macular degeneration. Unlike several other carotenoids, such as alpha and beta-carotene, lutein does not have pro-vitamin A activity. Spinach and other dark green leafy vegetables are good sources of lutein.
See the Linus Pauling Institute Micronutrient Information Center for more information.
L-Norvaline
An analog of the amino acid valine. L-Norvaline is an (in-vitro) inhibitor of the arginase enzyme, which breaks arginine down to ornithine and urea. Thus, L-norvaline is sometimes added to NO (nitric oxide) supplements as a “nitric oxide amplifier,” on the theory that inhibiting arginine breakdown can will enhance NO synthesis.
Inosine
A component of tRNA (transfer RNA) and is also a precursor to adenosine—a compound vital to energy production (as in ATP—adenosine triphosphate).
Inosine was once promoted as a strength/power supplement, but several studies on cyclists and runners have concluded that inosine supplementation does not improve athletic performance.
Huperzia serrata
Chinese club moss and source of Huperzine A. Standardized extracts of Huperzia serrata are often used in pre-workout supplements to enhance focus/concentration.
