L-Tyrosine Ethyl Ester
This page contains additional details information, clinical trials and research data pertaining to the ingredient L-Tyrosine Ehtyle Ester found in Lean Optimizer®, as well as its related chemical forms. You may print this page for your records if you wish.
General Information
Regular L-Tyrosine is not very use-effective by the body and hence, very LARGE dosages are needed. The Ethyl Ester version is up to 430% more bio-available and hence, more effective. Less is needed, and the results are faster.

The Benefits Of Tyrosine Supplementation
  1. Modulated the effects of acute stress. In one study acutely stressed rats on tyrosine supplementation displayed neither the stress-induced depletion of NE nor the behavioral depression. These preventive effects of tyrosine were abolished by co-administration of valine, a large neutral amino acid that competes with tyrosine for transport across the blood-brain barrier.

    Since tyrosine alone, in animals not subjected to stress, did not change NE turnover nor the behaviors studied, our observations affirm that catecholaminergic neurons respond to the precursor amino acid only when they are physiologically active. Supplementary tyrosine may be useful therapeutically in people exposed chronically to stress.

    In another study pre-treatment with supplemental tyrosine not only prevented the behavioral depression and hypothalamic NE depletion observed after an acute stress, but also suppressed the rise in plasma corticosterone. A few studies have shown that pretreatment with tyrosine reversed or prevented hypothermia-induced behavioral depression.8,9

    The results of these studies, and others,10 support a role for brain NE in stress and in stress-induced corticosterone secretion, and demonstrate that supplemental tyrosine can protect against several adverse consequences of such stress, and can enhance the synthesis of norepinephrine in stressed animals, thereby preventing both the neurochemical and the behavioral deficits seen with acute stress.11

  2. May be useful for weight loss. A recent study has shown that tyrosine improves some of the neurobiological disturbances of dietary restrictions without causing an increase in body weight.12

  3. Improves cognitive performance under stressful conditions. A study looking at the effects of the amino acid tyrosine on cognitive task performance found that supplementation with tyrosine may, under operational circumstances characterized by psychosocial and physical stress, reduce the effects of stress and fatigue on cognitive task performance.13 Another study found that tyrosine supplementation may sustain working memory when competing requirements to perform other tasks simultaneously degrade performance, and that supplemental tyrosine may be appropriate for maintaining performance when mild to severe decrements are anticipated.14,15

  4. Several studies have also shown that tyrosine supplementation may be effective in altering body composition.
Tyrosine As A Fat Loss Aid
One of the main mechanisms of most fat loss aids is the increase in stimulation of the sympathetic nervous (SNS) and central nervous (CNS) systems. Stimulation of these systems generally increases release of two hormones, called the catecholamines, and which are the primary mediators of lipolysis and thermogenesis in the body. The importance of this for dieters is a reduction of body fat.

Studies suggest that the pharmacological potency or duration of action of several sympathomimetics may be limited by the amount of endogenous substrate available for synthesis of the catecholamines. Therefore, supplemental tyrosine may prolong the appetite-reducing effects of anorexiants. For instance, one study demonstrated that supplementing with L-tyrosine overcame a tolerance to the appetite-reducing effects of phenylpropanolamine (PPA).16

Another study determined if the activity of mixed-acting sympathomimetic drugs could be restricted by the sympathetic neurons' ability to synthesis catecholamines.17 Researchers coadministered L-tyrosine with various mixed-acting anorexiants, including ephedrine, in hyperphagic rats. The addition of L-tyrosine potentiated the anorectic activity in a dose-dependent manner suggesting increased catecholamine synthesis in stimulated neurons.

In addition to (-)-ephedrine, L-tyrosine potentiated the appetite-reducing effects of several ephedrine isomers such as (-)-norephedrine, and (+)-pseudoephedrine. These substances are found in the most commonly used herbal source of ephedrine, Ma Huang.

In the same study, the coadministration of L-tyrosine to direct-acting beta2-adrenoceptor agonists, such as salbutamol, did not potentiate their anorectic activity. Because their mode of action is by direct stimulation of the beta2-adrenoceptors and not the release of stored catecholamines, L-tyrosine appears to specifically enhance activity of those drugs that preferentially release the catecholamines.

The lowest dose of anorexiant coadministered with L-tyrosine was as effective in appetite suppression as was the highest dose of the anorexiant alone. Thus, supplementing with L-tyrosine may allow for a significantly lower dose of anorexiant and still maintain a therapeutic response. Another response to several sympathomimetics is increased thermogenesis in brown adipose tissue (BAT). This additional mechanism is thought to enhance the weight loss induced by several sympathomimetics. While the potentiation of sympathomimetics by L-tyrosine appears to be centrally located, the response to prolonged sympathetic neuron stimulation in the periphery might be expected to be influenced by the concentrations of peripheral tyrosine and respond similarly.

However, although thermogenesis in BAT was induced by the sympathomimetics, supplementation with L-tyrosine failed to potentiate this effect in rats with the dosages used.18 The potentiation by L-tyrosine on the effects of several mixed-acting sympathomimetics appears to be largely relegated to centrally mediated effects in the brain. Aside from lack of potentiation of peripheral effects induced by sympathomimetics, 19,20 the potentiation by L-tyrosine is attenuated when L-valine is coadministered.21 A large neutral amino acid, L-valine competes with L-tyrosine for uptake into the brain and therefore reduces the effectiveness of L-tyrosine.

Although this may suggest that L-tyrosine be administered with no food in the stomach, there appears to be little if any antagonism between supplementation and food ingestion. Increased plasma tyrosine levels were measured in human subjects who were administered L-tyrosine (100 mg/kg/day) in three equally divided doses before meals containing a total daily intake of 113 grams of protein.22 Plasma tyrosine levels rose significantly after L-tyrosine ingestion and did not appear to affect plasma concentrations of the other neutral amino acids that compete with tyrosine for brain entry.

The former studies were conducted in murine models and may have limited applicability to humans. Unfortunately, no similar studies have been conducted in humans. However, some evidence suggests that supplementation with L-tyrosine may increase human catecholamine synthesis.23,24 A single dose of L-tyrosine (100-150 mg/kg) significantly increased urinary levels of NE, E, dopamine, and 3-methoxy-4-hydroxyphenylglycol (MHPG) within two hours after ingestion.25 The urinary catecholamines are derived from peripheral sources in the body, whereas urinary catecholamine metabolites reflect catecholamine status both peripherally and in the central nervous system (brain). Thus, increased urinary catecholamines and their metabolites may indicate that L-tyrosine supplementation may increase catecholamine synthesis and release from cells in the human body.

In all, coadministration of L-tyrosine has been shown in rats to potentiate the appetite-reducing effects of several sympathomimetics. This mechanism appears to be increased synthesis and release of the catecholamines in the brain. Although tyrosine is a substrate for the peripheral synthesis of catecholamines, supplementation of L-tyrosine was not shown to potentiate the sympathomimetic-induced thermogenesis in BAT of rats.

While studies show that administration of L-tyrosine in humans increases urinary catecholamines and their metabolites, no studies exist that examine potentiation of sympathomimetic-induced thermogenesis in humans. However, evidence of increased catecholamine synthesis and release after L-tyrosine administration in humans may substantiate the hypothesis that it may increase the thermogenesis induced by mixed-acting sympathomimetics. This response may be dosage dependent and larger doses than those given to the study rats may be required for humans.

1. Rudman D, Kutner M, Ansley J, et al. Hypotyrosinemia, hypocystinemia and failure to retain nitrogen during total parenteral nutrition of cirrhotic patients. Gastroenterology 1981; 81: 1025-35.
2. Rasmussen D. Effects of tyrosine and tryptophan ingestion on plasma catechloamine concentrations. J Clin Endo Metab 1983; 57(4):760-763.
3. Agharanya JC, Alonso R, Wurtman RJ. Changes in catecholamine excretion after short-term tyrosine ingestion in normally fed human subjects. Am J Clin Nutr 1981 Jan;34(1):82-7
4. Shurtleff D, Thomas JR, Shlers ST, et al. Tyrosine ameliorates a cold-induced delayed matching-to sample performance decrements in rats. Psychopharmacology 1993; 112:228-232, .
5. Owasoyo JO, Neri DF, Lamberth JG. Tyrosine and its potential use as a countermeasure to performance decrement in military sustained operations. Aviation Space and Enviromental Medicine 1992; 63:364-369.
6. Lehnert H, Reinstein DK, Strowbridge BW et al. Neurochemical and behavioral consequences of acute, uncontrollable stress: effects of dietary tyrosine. Brain Res 1984 Jun 15;303(2):215-23
7. Reinstein DK, Lehnert H, Wurtman RJ. Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats. Life Sci 1985 Dec 9;37(23):2157-63.
8. Rauch TM, Lieberman HR. Tyrosine pretreatment reverses hypothermia-induced behavioral depression. Brain Res Bull 1990 Jan;24(1):147-50.
9. Shurtleff D, Thomas JR, Schrot J, et al. Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacol Biochem Behav 1994 Apr;47(4):935-41.
10. Reinstein DK, Lehnert H, Scott NA, et al. Tyrosine prevents behavioral and neurochemical correlates of an acute stress in rats. Life Sci 1984 Jun 4;34(23):2225-31.
11. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull 1989 Apr;22(4):759-62.
12. Avraham Y, Bonne O, Berry EM. Behavioral and neurochemical alterations caused by diet restriction--the effect of tyrosine administration in mice. Brain Res 1996 Sep 2;732(1-2):133-44.
13. Deijen JB, Wientjes CJ, Vullinghs HF et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull 1999 Jan 15;48(2):203-9.
14. Thomas JR, Lockwood PA, Singh A, et al. Tyrosine improves working memory in a multitasking environment. Pharmacol Biochem Behav 1999 Nov;64(3):495-500.
15. Shukitt-Hale B, Stillman MJ, Lieberman HR. Tyrosine administration prevents hypoxia-induced decrements in learning and memory. Physiol Behav 1996 Apr-May;59(4-5):867-71.
16. Lehnert H, Wurtman RJ. Amino acid control of neurotransmitter synthesis and release: physiological and clinical implications. Psychotherapy and Psychosomatics 1993, 60:18-32.
17. Hull KM, Maher TJ. L-Tyrosine potentiates the anorexia induced by mixed-acting sympathomimetic drugs in hyperphagic rats. J Pharm Exp Ther 1990, 255:403-409.
18. Hull KM, Maher TJ. L-Tyrosine fails to potentiate several peripheral actions of the sympathomimetics. Pharm Biochem Behav 1991, 39:755-759.
19. Hull and Maher. Pharm Biochem Behav 1991. *** repeat citation - see #18
20. Hull KM, Maher TJ. Effects of L-tyrosine on mixed-acting sympathomimetic-induced pressor actions. Pharm Biochem Behav 1992, 43:1047-1052.
21. Hull and Maher. J Pharm Exp Therapeutics 1990. *** Repeat citation - see #17
22. Melamed E, Glaeser B, Growdon JH et al. Plasma tyrosine in normal humans: effects of oral tyrosine and protein-containing meals. J Neural Transm 1980, 47:299-306.
23. Agharanya JC, Alonso R, Wurtman RJ. *** repeat citation - see #3
24. Melamed E, Glaeser B, Growdon JH et al. *** repeat citation - see #22
25. Alonso R, Gibson CJ, Wurtman RJ, et al. Elevation of urinary catecholamines and their metabolites following tyrosine administration in humans. Biol Psychiatry 1982, 17:781-790.

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