Insulin-Muscle Recovery Connection
by Edmund Burke, PhD
Many runners now understand the link between sports performance and nutrition. They have developed an understanding of the types of foods to eat and the types of foods to avoid. However, many runners don't truly understand how to use sound nutritional practices to recover from exercise bouts. An example of this is the number of athletes who are turning to the 40-30-30 in the hopes of seeing improved performance.
Athletes on this diet plan obtain 40% of their calories from carbohydrate, 30% from fat and 30% from protein, in contrast to the 60-25-15 ratio that has traditionally been recommended by nutritionists. Supporters of the 40-30-30 plan say that decreasing carbohydrate intake and boosting protein consumption will enable dieters to burn more fat. They contend that, for athletes, this translates into a glycogen-sparing effect, which can extend endurance.The theory behind the 40-30-30 diet is that a lower carbohydrate intake, coupled with an increased percentage of protein, will help to keep insulin levels low in the blood. There are two problems with this theory. One, it has not been verified by research. Two, the majority of scientists and nutritionists involved in performance research know that insulin is not the culprit in causing obesity.
Insulin is a very important hormone in the recovery process, especially following a hard workout or competition. It is essential for processing carbohydrate and protein into your muscle cells. Because it is so crucial to recovery and muscle performance, insulin should be termed the "master recovery hormone."
Insulin & Glycogen Replenishment
A hormone that is found in the pancreas, insulin is released when you consume carbohydrate. A primary function of insulin is to facilitate the transport of carbohydrate, specifically glucose, from the blood into the muscle cell, where it can be metabolized to produce energy that will enable the muscle cell to do work. Insulin levels are a critical factor in regulating muscle glycogen synthesis.
The manufacture of muscle glycogen from glucose requires the presence of an enzyme called glycogen synthetase. Insulin stimulates this enzyme, enabling the glycogen manufacturing process to proceed at a faster rate.
Assuming that sufficient amounts of carbohydrate are available, the greater the plasma insulin levels after exercise, the faster the transport of glucose into the muscle cell and the faster the rate of muscle glycogen synthesis. Timing of this process is key.
The muscle cell is maximally sensitive to insulin up to two hours after exercise. Thus, glycogen stores should be replenished immediately after exercise. Consuming 50 grams of carbohydrate four hours after exercise will produce very different results than consuming the same amount of carbohydrate 30 minutes after exercise. This effect is often ignored by the serious athlete.
Dr. John Ivy, University of Texas at Austin, has found that muscle cells are highly sensitive to insulin during this time. This means that when a sufficient source of carbohydrate is present, glycogen replenishment occurs rapidly. In fact, glycogen synthesis in the two-hour period post-exercise proceeds two to three times faster than normal. If a carbohydrate supplement is not consumed during this period of time, the muscle will become insensitive to insulin and the rate of glycogen recovery will be significantly slowed.
Because the insulin response is vital in the muscle recovery process, researchers have investigated how insulin can be further stimulated after exercise. These studies have important implications for the athlete. Researchers have shown that when protein is added to carbohydrate the insulin response is almost doubled. Thus it would appear logical that any sports drink with protein and carbohydrate offers an advantage in the recovery process. However, too much protein can slow gastric emptying, thereby slowing fluid and glycogen replacement.
The challenge is how to gain the benefits of protein without the negative effect on gastric emptying. There is a critical ratio of carbohydrate to protein, termed the Optimum Recovery Ratio. When the ratio of carbohydrate to protein is 4 to 1(for example 56 grams of carbohydrate and 14 grams of protein), the insulin stimulating action of protein does not appear to interfere with the essential rehydration phase.
Specific amino acids within protein have been found to also increase glycogen replenishment. Studies have shown that the amino acid arginine increases muscle glycogen replenishment in the recovery period by increasing the post-exercise utilization of fat as an energy source. By increasing the utilization of fat, more glucose is available to help rebuild depleted muscle glycogen stores.
These studies have important implications for the athlete. First, insulin stimulation is essential immediately following exercise. Second, the addition of arginine and protein with the correct ratio of carbohydrates can improve performance by promoting a faster recovery.
Insulin and Rebuilding of Muscle Protein
In addition to playing a role in reducing protein breakdown and increasing carbohydrate replenishment, insulin is involved in the protein rebuilding process. Insulin increases protein synthesis by facilitating the transport of amino acids into the muscle cell. Amino acids are the building blocks of protein. By making sure the muscle cell has the necessary amounts of these essential building blocks, insulin enables the cell to produce proteins necessary for maintaining cell structure and function.
Enhancing Endurance and Speeding Recovery
At the 1999 national meeting of The American College of Sports Medicine, two groups of investigators reported the results of studies of Endurox R4, a new sports drink specifically designed to stimulate insulin. It contained carbohydrate and protein in a 4:1 (4 grams of carbohydrate to 1 gram of protein) ratio, plus arginine. The carbohydrate consisted primarily of high glycemic index sugars.
This drink was tested against the leading sports drink. Investigators found that the R4 drink increased insulin levels by 70%.
Most importantly from an athlete's perspective, the R4 drink was also proven to increase endurance by 55% and reduce post exercise muscle damage by 36%.
These results indicate that stimulation of insulin, especially in the 0-2 hour recovery period, can have a dramatic effect on recovery and athletic performance.