It is known that amino acids taken in one’s diet and are termed as “essential,” activate the synthesis of protein in human beings. Of these, a particular amino acid – leucine – may play a more significant role by stimulating synthesis and preventing the degradation of muscle protein as well. This study attempted to see if a concentration of leucine allowed for more protein synthesis in the muscles of both men and women. Results showed that at least 10 grams of essential amino acid (EAA) intake with a high concentration of leucine allows for maximum muscle protein synthesis in young men and women.
Studies have shown in the past that essential amino acids in the diet can stimulate growth of muscle protein in both humans and animals. Studies have also shown that the leucine content of the EAA, alone, can even perform this activity. Leucine has also been shown to prevent breakdown of muscle proteins. This special property has made leucine the target of multiple studies over the years to improve muscle building and to prevent its breakdown. But the actual mechanism by which leucine provides this benefit is yet unclear. Also, there are studies that have shown that benefits of leucine are largely effective in animals, while human studies have shown varying and contradicting results. The current study was conducted to establish the role of leucine in muscle mass stabilization.
* For this study, a total of six healthy men and eight healthy women were included.
* The study group was equally divided into two groups. One group received EAA (10 g) with 1.8 g of leucine and the other group received EAA (10 g) with 3.5 g of leucine. The former group was called the control group while the latter group was called the leucine group.
* After intake, the subjects were tested for three hours. This included various tests to determine muscle protein synthesis and breakdown and the level of leucine.
* Results showed that blood concentration of leucine and the amount of leucine transferred to the leg muscles was higher in the leucine group compared to the control group. But the amount available within the muscle cells was similar in both the groups.
* After an hour of intake of the EAA, both the groups showed a similar rise in muscle protein synthesis process. However, protein breakdown in the participants’ muscles was significantly less in the leucine group after an hour of intake of the EAA.
* The results also showed that a specific targeting system called the “mTOR” signaling system that allows for fewer muscle breakdowns was activated by leucine. This was speculated to be the reason for the efficacy of leucine.
The authors agree that in this study a high blood concentration of leucine did not mean a high muscle concentration of leucine due to improved transmission of the amino acid into the muscle. They suggest that this is an important consideration in the utilization of leucine in the muscles and should be kept in mind. They also suggest further studies to evaluate the mechanism by which leucine acts on the muscles.
From this study, the authors conclude that when 10 g of EAA is given with a higher concentration of leucine, it leads to better muscle protein buildup and less muscle protein breakdown. In short, it leads to muscle protein stabilization. However, this study also shows that although blood levels of leucine are higher with a high concentration of leucine ingestion, the muscle concentration does not change. This means high blood concentration does not always translate into higher muscle concentration. The authors suggest that the clinical importance of this special benefit offered by leucine remains to be seen in further larger studies. The authors find that a leucine concentration of 1.8 g in an amino acid mixture may be sufficient in improving muscle protein buildup, while a higher concentration of leucine may prevent breakdown of muscle proteins as well.
For More Information:
Leucine Intake Enhances Growth and Prevents Protein Breakdown in Muscles
The Journal of Nutrition, September 2010
By Erin L. Glynn; Christopher S. Fry
From the University of Texas Medical Branch, Galveston, Texas