L-Tyrosine

What is it? Tyrosine is an amino acid which is an essential precursor or "building block" to the neurotransmitters responsible for maintaining metabolic rate. L-Tyrosine is the direct precursor to stimulatory neurotransmitters such as epinephrine and noropenephrine (i.e. adrenaline) as well as certain thyroid hormones and dopamine.
In other words, L-Tyrosine is a precursor to important stimulants to the metabolism. It is also considered a non carbohydrate ATP substrate.
Tyrosine is a precursor to CCK (see section on glycomacropeptide for a discussion on the effects of CCK). High amounts of tyrosine are found in foods high in protein. The body can make tyrosine from the amino acid phenylalanine.
What is it supposed to do?
As the above would imply, tyrosine is an important amino acid for maintaining a higher metabolic rate. As people reduce their calories during a diet, less tyrosine is available to make the natural stimulants to metabolism. Therefore, the metabolism slows down making it harder to lose weight.
Less building blocks for stimulants means a slower metabolism. This is an overly simple explanation, but you get the idea.
This may be one more way the body has built its own safely net to respond to less calories being eaten. By taking L •tyrosine as a supplement you supply the building blocks to these important neurotransmitters responsible for maintaining metabolic rate. This may allow the dieter to bypass some of the metabolic down regulation from a reduced calories diet, thus maintaining a higher metabolic rate making weight loss easier and avoiding plateaus.
Tyrosine may also act as an anorectic (appetite suppressing) supplement via its effects on CCK and other mechanisms. Tyrosine is also sold as a mild stimulant and some feel it may be useful for depression. Under stressful conditions, food sources and phenylalanine to tyrosine conversion may be inadequate to maintain the essential neurotransmitters needed for optimal performance.
What does the research have to say?
The research with tyrosine as a weight loss agent is limited. However, there are studies showing tyrosine can potentiate the anorectic effects of other weight loss compounds, such as phenylpropanolamine and ephedrine making their effects more prolonged and effective. Several animals studies demonstrated that tyrosine is a powerful potentiator of the appetite suppressing qualities of the ephedrine based supplements.
Although human studies using tyrosine mixed with ephedrine are limited, one would expect similar results as found in animals. Because of the extreme complexity of human metabolism and appetite control, effects in people may not be as dramatic as those seen with animals
Tyrosine does not appear to increase the thermogenic effects of the ephedrine caffeine products, but work at the level of the brain to reduce food intake and maintain the availability of stimulatory neurotransmitters. There is research suggesting that the positive effects of ephedrine and other compounds are actually limited by the availability of L-tyrosine.
One area tyrosine shines in the research relates to its effects on mental acuity and stress. The military has been particularly interested in tyrosine for use with troops. Tyrosine may also have direct applications to athletes in rigorous training susceptible to Over Training Syndrome (OTS).
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