Proper Timing of Amino Acids and Carbohydrates:
can they increase protein synthesis?


Tom McCullough, MEd.

What happens to the muscle tissue during exercise?

During a bout of exercise catabolic responses cause the proteins and muscle tissue to be broken down. Obviously the higher the intensity of the exercise the more catabolic the response will be. Meaning the more protein and muscle tissue is broken down while exercising. During the exercise phase there are loses in vitamins, minerals as well as increases in the adrenal production of catecholamines and glucocorticoids. So cortisol increases, glucagon increases, and insulin decreases. Thus, protein tissue degradation increases and protein synthesis decreases or stops while in the exercise phase.

Post exercise

Immediately after exercise in the post-exercise phase, a restorative rebound in the naturally occurring anabolic hormones occurs. These hormones include insulin, growth hormone (GH), IGF, pineal and thymic factors, as well as the steroid hormones testosterone, DHEA, and estrogens. This post-exercise response is also known as biochemical or metabolic supercompensation. During this supercompensation period HIGH LEVELS of these anabolic hormones, particularly INSULIN, GH, and IGF, are NECESSARY during close post-exercise restorative phase to provide MAXIMAL PROTEIN SYNTHESIS. High levels of these same hormones are also necessary to restore the negative metabolic effect created by catecholamines and glucocorticoids produced during exercise. It should be noted that testosterone is highest during mid-exercise but falls off slightly immediately post-exercise. It does not seem to be involved in the earlier stages of post-exercise as the hormones insulin, GH, and IGF. Testosterone usually appears again during later phases of post-workout recovery. So this tells us that immediately following a bout of exercise, there will be an increase in the production of both GH and INSULIN. Both INSULIN and GH ARE very necessary for optimal protein synthesis.

It should also be noted that literature does support the theory that INSULIN and GH both INCREASE protein synthesis in combination with several other natural occurring hormones. In fact, insulin rebound is required for the release of GH, which in turn releases IGF. It should also be noted once again that synthesis will not be able to occur if there is not a sufficient supply of energy (as in calories) or insufficient free amino acid pools. Thus, many of these sources revealed as I had previously recommended, that amino acid or protein supplements with some added carbs, taken within 2 hours post-exercise, while insulin, growth hormone (GH), IGF, pineal and thymic factors are high, further aids in creating a beneficial environment during recovery by further increasing these hormone levels.

Post-exercise carbs

The addition of dietary carbohydrate causes increases insulin production, which further increases GH release, which in turn further increases the release of IGF. These increases in turn, have been shown to further increase protein synthesis and muscle growth after a bout of exercise as well as increasing the uptake of amino acids. By adding amino acids after exercise we have further increased the available free amino acid pool as well. Amino acids are necessary for protein synthesis to take place. So without the insulin rebound after exercise, the body would remain in a catabolic state.

Let�s examine more closely why it is suggested that carbohydrate be taken with protein immediately following a bout if exercise. We know that with the onset of exercise, ATP is the immediate source of energy. As the exercise progresses, the ATP stores are reduced and glycogen and glucose are also utilized by the muscle for fuel. With more muscle glycogen and glucose being used for energy, blood glucose levels soon begin to drop. Insulin levels soon begin to fall as well. This is the point at which FFA is released from the adipose tissue and becomes a reserve source of fuel.

As we near the end of our training, the body is now in a hypoglycemic stage. The blood sugar is low and the insulin level has dropped. Immediately after exercise as explained earlier, GH production is increased as insulin levels start to rebound. A carbohydrate supplement following exercise will elevate blood glucose levels and cause a state of hyperglycemia forcing further production of insulin. The high levels of insulin in the blood now force much needed glucose and amino acids through the receptor sites in the muscle cell at a quicker rate. This high level of blood glucose will eventually cause further GH secretions. Soon the high levels of insulin utilize the extra carbohydrate and the blood glucose levels once again drop. Of course the insulin level now drops as it did during exercise. GH secreats once again starts as the rebound effect begins all over.

Is Insulin Really a Monster Hormone ?

For someone who leads a sedentary lifestyle, these big insulin swings created by a high carbohydrate post-exercise meal would not be considered very beneficial. However, for a strength athlete, these types of swings can create optimal conditions for both protein synthesis and anabolic hormone production. This is why most sport nutritionists believe that it is very important to not only time eating, but to properly time supplementation. Some bodybuilders have taken this theory a step further by actually using insulin injections to create much larger swings and a bigger rebound effect. However, this might be very effective, it is also considered very dangerous and might eventually lead to a decrease in natural production of insulin by the pancreas.


How much of each would I recommend? About 0.7 g of protein/kg of body weight with 2 g of carbohydrate/kg of body weight in the first 15-30 minutes after training. Only consume simple carbohydrates like glucose or sucrose or other high glycemic index foods. Not complex carbohydrates or low glycemic food or fructose. The protein source should be high in branched amino acids. I also recommend using a liquid full spectrum amino acid mixture with di- and tri-peptide bonds. Full spectrum amino acids are absorbed quicker due to their small chain structure. Therefore they get into the bloodstream very quickly where they are shuttled quickly into the muscle cell by the increased insulin production.

In summary, it should be easily understood now that the rebound effect or rises in the anti-catabolic hormones insulin, growth hormone (GH), IGF, pineal and thymic factors, occur immediately after exercise is stopped. The steroid hormones testosterone, DHEA, and estrogens naturally start to occur later in the post-exercise phase. The combination of these hormonal actions stops the protein and muscle degradation caused by catabolic hormones produced during exercise and starts protein synthesis after exercise.


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