Phenylalanine comes in several forms as a supplement:
L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
DL-phenylalanine, which contains both the D- and L-forms
Beta-alanine is marketed as a way to enhance sports performance and endurance. Some scientific evidence backs such uses, but the studies have been small and the results inconclusive.
Here's how it's said to work. Muscles contain carnosine. Higher levels of carnosine may allow the muscles to perform for longer periods before they become fatigued. Carnosine does this by helping to regulate acid buildup in the muscles, a primary cause of muscle fatigue.
Beta-alanine is one of carnosine's main ingredients. Beta-alanine supplements are thought to boost the production of carnosine and, in turn, boost sports performance.
However, a review of studies of the beta-alanine supplement shows that it doesn't increase muscle strength or aerobic endurance. Instead, it appears to slightly increase the amount of time an athlete can perform high-intensity exercises, such as weight lifting and sprinting, before getting exhausted.
This does not necessarily mean that athletes will see better results. In one study, sprinters who took beta-alanine did not improve their times in a 400-meter race.
It's not clear exactly what benefits can be gained from taking beta-alanine supplements. Some research suggests that boosting the levels of carnosine in the muscles may take weeks of using supplements.
Standard doses have not been established. Also, quality and active ingredients in supplements may vary widely from maker to maker. This makes it hard to establish a standard dose.
Can you get beta-alanine from food?
Food sources of beta-alanine and carnosine include:
Poultry (especially white meat like that found in chicken breasts)
What are the risks of taking beta-alanine supplements?
Some people have reported tingling of the skin after taking large doses of beta-alanine. The symptoms usually subsided after about an hour and a half.
The U.S. Food and Drug Administration (FDA) does regulate dietary supplements; however, it treats them like foods rather than medications. Unlike drug manufacturers, the makers of supplements don’t have to show their products are safe or effective before selling them on the market.