Recent research suggests that eating a sufficient amount of protein will help maintain or even increase muscle development. This has lead to the production and commercialization of a number of protein supplements designed to stimulate muscle protein synthesis. Such products are used to enhance the effects of resistance exercise on muscle mass and strength, recover rapidly from strenuous exercise, or to ensure an adequate amount of dietary protein is consumed to limit aging muscle loss. However, in developing these products usually little consideration is given to the role carbohydrates play in muscle development.
CERTAIN AMINO ACIDS ACTUALLY TURN ON THE CELLULAR MECHANISMS THAT ACTIVATE PROTEIN SYNTHESIS.
When we eat protein, it is broken down to its natural building blocks, amino acids. These amino acids enter the circulation and are delivered to all tissues of the body. The amino acids are then used to repair and develop new tissue, including skeletal muscle. This process is called protein synthesis. Certain amino acids actually turn on the cellular mechanisms that activate protein synthesis. The primary amino acid responsible for this action is leucine.
Leucine activates a cellular enzyme named mammalian target of rapamycin, or simply mTOR. mTOR is responsible for turning on other cellular enzymes responsible for assembling amino acids that have been broken down from dietary protein into new muscle proteins such as myosin and actin.
FOR MIDDLE AGE AND OLDER ADULTS, ABOUT TWICE AS MUCH DIETARY PROTEIN WILL BE REQUIRED AS THAT CONSUMED BY YOUNG ADULTS.
The amount of leucine required to maximally activate muscle protein synthesis depends on one’s age. For young adults it is approximately 2 grams. For middle age and older individuals it is about 4 grams. Not all dietary proteins contain the same amount of leucine. Therefore, the type as well as the amount of protein in a protein supplement will determine how effective it will be in activating muscle protein synthesis. For example, the leucine content of whey is about 10.5 g/100 g protein, and that of soy and rice protein are 7.7 and 6.4 g/100 g protein, respectively.
To be clear, we are not talking about 100 grams of whey, soy or rice, but the isolated protein from these foods. Now, if 2 grams of leucine are required to maximally turn on muscle protein synthesis in young adults, we can easily calculate that they will have to eat approximately 20 grams of whey protein, 26 grams of soy protein and 31 grams of rice protein to maximally activate protein synthesis. For middle age and older adults, about twice as much dietary protein will be required as that consumed by young adults.
However, it is possible to provide a smaller amount of protein and combine it with free leucine to achieve the same rate of muscle protein synthesis. For example, 20 grams of whey protein along with 2 additional grams of leucine will have the same effect on older adults as 40 grams of whey protein.
MUSCLE PROTEIN, LIKE ALL PROTEIN IN THE BODY, IS CONSTANTLY BEING SYNTHESIZED AND BROKEN DOWN.
But, how do carbohydrates contribute to muscle development? When considering muscle development, the rate of protein synthesis is only part of the equation. Muscle protein, like all protein in the body, naturally turns over. In other words, it is constantly being synthesized and broken down. Therefore, protein development or accretion is the difference between the rate of synthesis and the rate of breakdown. Muscle development occurs when the rate of synthesis is faster than the rate of breakdown.
Conversely, muscle atrophy or loss of muscle occurs when the rate of synthesis is slower than the rate of breakdown. By consuming protein, we are able to raise the rate of muscle protein synthesis above the rate of breakdown, at least for several hours, and promote an increase in skeletal muscle development. But it is also possible to reduce the rate of muscle breakdown, and by reducing the rate of muscle breakdown while also increasing the rate of protein synthesis the rate of muscle development is accelerated.
CONSUMING A SMALL AMOUNT OF CARBOHYDRATE IN COMBINATION WITH A PROTEIN SUPPLEMENT SLOWS THE RATE OF MUSCLE PROTEIN BREAKDOWN.
So how do we reduce the rate of muscle protein breakdown? This is where carbohydrates comes into play. Carbohydrates, particularly simple sugars such as glucose, fructose and sucrose, when consumed effectively increase the secretion of insulin from the pancreas, and raise the blood insulin level. When these sugars are combined with protein, even very small amounts can have a robust effect on insulin secretion.
A rise in blood insulin has a number of effects on skeletal muscle including helping to activate mTOR and increase muscle protein synthesis. It also activates the enzyme eNOS resulting in an increase in nitric oxide. Nitric oxide causes vasodilation of the blood vessels in the muscles improving muscle blood flow, and enhancing nutrient delivery to the muscles. It is also an activator of satellite cells that are embedded around the muscle fibers, and are involved in muscle development.
However, the most important effect insulin has on muscle development is that it activates cellular enzymes and signaling proteins that block muscle protein breakdown. So by consuming a small amount of carbohydrate in combination with a protein supplement, not only is the rate of muscle protein synthesis increased, but the rate of muscle protein breakdown is slowed. The end result is a very rapid rate of muscle development.
By consuming a protein supplement without added carbohydrate, will significantly reduce its effectiveness to stimulate muscle development and protect your muscle mass.
So remember, when you see a small amount of carbohydrate in a protein supplement, it is not being added to improve taste. It is being added to improve its efficacy.