“We believe that leucine is the trigger for protein synthesis,” said Dr Ralf Jaeger, PhD, FISSN, President of Milwaukee-based consultancy Increnovo LLC
“From a sports nutrition point of view, the branched chain amino acids (BCAAs) – leucine, iso-leucine, valine – are unique among the essential amino acids for their role in protein metabolism and neural function,” he said.
“The research has narrowed down from whole proteins to amino acids. BCAAs are a group of similar essential amino acids: leucine, isoleucine, and valine - they make up about 1/3 of muscle protein. They work together to rebuild muscle protein, which is dismantled by exercise, and act as fuel for exercise,” Susan Kleiner, PhD, told NutraIngredients-USA. Kleiner is a sports nutrition formulation expert and the author of Power Eating, Fourth Edition (Human Kinetics, 2013).
“The harder you work out, the more leucine your body will use. After aerobic exercise, plasma leucine levels drop 11-33 %. After strength training exercise, they drop 30%. High intensity exercise drains skeletal muscle stores of leucine,” she said.
Amino acids work together
Early iterations of sports products focused on leucine, because of its front and center role in the function of skeletal muscles. But leucine is only part of the story, Jaeger said.
“Research shows that BCAAs are able to stimulate skeleton muscle protein synthesis to the same degree as all 9 essential amino acids, so those three are really key.
“When we examine further, only leucine was able to stimulate protein synthesis independently. However, leucine on its own is not effective, so you need leucine and the other amino acids, too,” he said.
“Leucine is like the hot button catalyzing muscle protein synthesis. While muscle protein synthesis happens after exercise, how quickly it begins and ramps up to a high rate depends on having the right amount of leucine around. But you still need all the essential amino acids for complete synthesis. And BCAAs make up such a large proportion of muscle protein,” Kleiner said.
BCAAs targeted for recovery
While BCAAs cannot substitute for whole proteins, they can form the basis of products targeted as muscle fuel during exercise and to aid recovery. MusclePharm, a leader in the sports nutrition category, uses a proprietary blend of 3 parts leucine, 2 parts valine and 1 part isoleucine in its Amino 1 performance recovery fuel product.
“The formulation was created by observing multiple protein sources that we thought were valuable. In the past was what other companies had done was come out with a heavy leucine product,” said Dr Michael Kim, MusclePharm’s director of medicine, education and research.
“The body can absorb them without doing any break down. There is instant gratifaction for the hungry muscles,” Kim said.
MusclePharm markets a full line of whole protein products, but uses the BCAAs for use immediately before, during and after heavy exercise, whereas the whole protein products are meant more for daily supplementation
“What we’ve forgotten is the practice of recovery. We’re always ready to do the movement, and we’re already to do the go. The one thing people don’t do is they don’t recover well,” he said.
Convenience plays a role
“You could just eat enough protein foods to get what you need, if the amounts and proportions are correct. The timing of consumption, before and after training, is also important. So convenience is a big factor," Kleiner said.
"In any single serving the goal is to get at least 2.5 g of leucine. Whey protein is about 10% leucine, the highest of all proteins. So you need at least 25 g of whey protein isolate to get 2.5 g leucine. Other protein sources require higher serving sizes to get enough leucine,” she said.
“But what can you consume without feeling too full before exercise, and what can you consume without much appetite after exercise? Liquids that empty quickly from the stomach, and that's the beauty of the supplements,” said Kleiner.