October 30, 2002 |
An amino acid supplement called L-tyrosine, recommended by fitness trainers and sold by supplement outlets as an endurance booster, has no effect on endurance, according to a new Brigham Young University study. “There wasn’t any indication from our tests that tyrosine had an effect in the blood or in the brain,” said Allen Parcell, assistant professor in the Human Performance Research Center at BYU. “Tyrosine didn’t improve endurance performance in our subjects.” From the Brigham Young University :Amino acid supplement L-tyrosine fails to boost endurance, BYU study shows
Stick with carbs, researchers say
PROVO, Utah?An amino acid supplement called L-tyrosine, recommended by fitness trainers and sold by supplement outlets as an endurance booster, has no effect on endurance, according to a new Brigham Young University study.
“There wasn’t any indication from our tests that tyrosine had an effect in the blood or in the brain,” said Allen Parcell, assistant professor in the Human Performance Research Center at BYU. “Tyrosine didn’t improve endurance performance in our subjects.”
The results of the study, funded in part by the Gatorade Sports Science Institute, will be reported in the November issue of the “Journal of Applied Physiology,” one of the top journals in the field of exercise science.
The BYU team followed up on previous studies in animals that suggested the possibility of “fooling” the brain to prevent fatigue. Tyrosine travels through the same portal to the brain as does tryptophan – the amino acid in turkey meat that makes people drowsy after Thanksgiving dinner. The thinking was that extra tyrosine would block the tryptophan, allowing the user to avoid the sensation of fatigue.
“There is clear evidence that your psychological situation influences your ability to exercise,” Parcell said. “We were trying to reduce inhibition within the central nervous system.”
Tyrosine tablets are available from most supplement providers and are recommended on some sports Web sites for increasing endurance. They are also touted as mood enhancers, a capability the BYU team did not explore.
To go beyond brain chemistry and put tyrosine to the test in a real-world application, Parcell and his colleagues standardized the diets and exercise regimens of nine cyclists. They then conducted time trials, giving each cyclist a sports drink. Some of the drinks contained tyrosine, others a basic carbohydrate like glucose and others a combination of both.
In the end, the cyclists taking tyrosine saw no change in their endurance. Those drinking the carbohydrates did improve, a result also observed in previous studies.
“In most cases a well-balanced diet with an emphasis on carbohydrates has definitely been shown to significantly improve endurance,” Parcell said.
Parcell thinks, and one previous study in humans seems to indicate, that tyrosine’s effect on endurance would only kick in after long periods of physical activity – five or more hours. The BYU tests lasted no longer than 2.5 hours.
“Maybe there’s a case to pursue something like this with some ultra-endurance, really long-term exercise,” Parcell said.
So except for possibly Ironman triathletes, people looking to enhance their workouts should stick with tried-and-true performance boosters like sports drinks and bars that provide carbohydrates, Parcell recommended.
“As far as legal, over-the-counter stuff, there really isn’t anything out there aside from carbohydrates,” Parcell said. “There has not been any unequivocal data on any nutritional supplement that’s been shown to really enhance performance beyond a placebo effect.”
The lead author on the study is Troy D. Chinevere — the research was his doctoral dissertation. In addition to Parcell, other co-authors are Robert D. Sawyer and Andrew R. Creer, current BYU graduate students; and Robert K. Conlee, dean of BYU’s College of Health and Human Performance.