Evidence mounts for carb-protein sports drink mix

Pro triathlete Jan Wanklyn fuels during an Ironman triathlon  Credit: Robert Laberge/Allsport
Thirty-five years ago, a physiologist at the University of Florida created the first sports drink.

Dr. Robert Cade hypothesized that the addition of electrolyte minerals and carbohydrate to water would facilitate fluid replacement and provide an energy source to working muscles, thereby enhancing athletic performance and delaying fatigue.

Clinical trials of this revolutionary new sports fuel showed that it did in fact enhance athletic performance and delay fatigue more than plain water.

Sports drinks hydrate athletes better because they replace not only the water content but also electrolytes such as sodium that are lost in sweat.

The result is less accumulation of heat in the body, less stress on the cardiovascular system, and less chance of muscle cramping, all of which adds up to better performance.

In addition, hundreds of studies have confirmed that the carbohydrate content of sports drinks delays fatigue additively. Carbohydrate is the main fuel that powers the muscles during exercise.

Athletes typically become fatigued when they run out of a special type of carbohydrate fuel called glycogen, which is stored in their muscles. The supply of glycogen in the muscles is limited. However, drinking a sports drink during exercise gives the muscles an alternative source of energy, allowing them to hold onto their glycogen supply longer so the athlete can train and compete more intensely for greater durations.

The conventional sports drink formula of 6-8% carbohydrate, plus enough electrolytes to offset sweat losses, proved so effective that it has remained essentially unchanged for decades.

However, in the 1990s, exercise physiologists began to experiment with adding protein to the conventional sports drink formula. They found that the addition of protein produced a stronger insulin response, resulting in faster transport of both carbs and protein into muscle cells.

The significance of this insulin boost is that faster carbohydrate delivery during exercise allows the body to conserve its stored carbohydrate, delaying fatigue.

Also, conservation of stored carbohydrate during exercise reduces the release of the stress hormone cortisol, which breaks down muscle tissue. And after exercise, consuming a sports drink with protein results in much faster muscle recovery than consuming a regular sports drink.

The following studies demonstrate the benefits of a carbohydrate-protein sports drink mix:

Zawadzki KM , Yaspelkis BB , Ivy JL. "Carbohydrate protein complex increases the rate of muscle glycogen storage after exercise." Journal of Applied Physiology 1992; 72:1854-9.

Researchers at the University of Texas compared the use of carbohydrate, protein, and carbohydrate-protein supplements to see whether they could speed up the replenishment of muscle glycogen after prolonged exhaustive exercise.

Nine men cycled for two hours on three occasions to deplete their muscle glycogen. Right after each 2-hour bout, they ingested a carbohydrate, protein, or carbohydrate-protein supplement. Blood and muscle tissue was sampled throughout recovery.

The replenishment rate of muscle glycogen storage during the carbohydrate-protein treatment was 38% greater than carbohydrate only, and over three times faster than the protein treatment.


ES Niles, T Lachowetz, J Garfi, W Sullivan, JC Smith, BP Leyh, SA Headley. "Carbohydrate-protein drink improves time to exhaustion after recovery from endurance exercise." Journal of Exercise Physiology online, 2001 4:45-52.

Ten men were studied to investigate the effects of two different supplements on endurance; one a carbohydrate drink and the other a carbohydrate-protein drink of equal calories. After a muscle-glycogen-lowering exercise, the two drinks were administered with a 60-minute interval between dosages.

The athletes went 20% longer when using the carbohydrate-protein drink than when using the carbohydrate-only drink, which correlated with elevated insulin in the carbohydrate-protein condition.

The researchers concluded that a carbohydrate-protein drink consumed after glycogen-depleting exercise might lead to a faster rate of muscle glycogen re-synthesis than a carbohydrate-only beverage.

This would hasten the recovery process and improve exercise endurance during a second bout of exercise performed on the same day.


JL Ivy, HW Goforth Jr, BM Damon, TR McCauley, EC Parsons, TB Price. "Early post-exercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement." Journal of Applied Physiology 93: 1337-1344, 2002.

This group compared a carbohydrate-protein supplement and a carbohydrate supplement of equal calorie content. After 2.5 hours of intense cycling to deplete their thigh muscles of glycogen, the subjects received either drink.

After four hours of recovery, muscle glycogen was the higher for the carbohydrate-protein treatment when compared with the carbohydrate treatment.


SL Miller, KD Tipton, DL Chinkes, SE Wolf, RR Wolfe. "Independent and combined effects of amino acids and glucose after resistance exercise." Medicine and Science in Sports and Exercise. 2003, 35:449-55.

This study assessed the separate and combined effects of amino acids and/or carbohydrate (consumed at one and two hours after weightlifting) on muscle protein metabolism.

Volunteers performed leg exercise and then ingested one of three drinks -- amino acids (protein), carbohydrate, or amino acids and carbohydrate (carbohydrate-protein) -- at one and two hours after exercise.

The greatest uptake of protein three hours after exercise was with carbohydrate-protein, and was least in carbohydrate. In fact, the carbohydrate-protein drink was 38% more effective than the protein drink in re-synthesizing muscle proteins (weightlifters take note).

This means the muscle is gathering the pieces to make new protein. This study concludes that more protein is taken up by the muscle when the protein is mixed with carbohydrate -- more evidence that a drink containing a mixture of carbs and protein is more effective than either alone.


MB Williams, PB Raven, DL Fogt, JL Ivy. "Effects of recovery beverages on glycogen restoration and endurance exercise performance." Journal of Strength and Conditioning Research 2003; 17:12-9.

This study compared a high carbohydrate-protein beverage containing electrolytes and a traditional carbohydrate-electrolyte sports beverage.

After a glycogen-depleting exercise, each subject exercised to exhaustion at 85% of VO2max. Ingestion of the carbohydrate-protein beverage resulted in a 92% greater insulin response, a 128% greater storage of muscle glycogen compared with the carbohydrate, and a 55% increase in endurance performance in the second exercise bout.

These findings indicate that the rate of recovery after exercise is coupled with muscle glycogen replenishment, and suggests that recovery supplements containing protein and carbohydrate should be used to maximize muscle glycogen as well as fluid replacement.


JL Ivy, P Res, Z Ding, MO Widzer. "Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity." International Journal of Sports Nutrition and Exercise Metabolism (in press).

This study compared a carbohydrate and a carbohydrate-protein supplement on endurance performance. Trained cyclists exercised at variable exercise intensities for three hours, then they cycled at 85% VO2max until exhausted.

Two hundred milliliters of each of the three supplements (water, carbohydrate, carbohydrate-protein) was provided every 20 minutes.

The carbohydrate-protein drink increased time to exhaustion by 36% over the carbohydrate supplement, and 55% over water.

Conclusion

When the earliest carbohydrate-protein sports drink studies were published, many experts were skeptical. After all, promising new leads in sports nutrition turn out to be dead ends all the time.

But as study after new study confirms the benefits of adding protein to a sports drink, a consensus is forming that carb-protein is in fact a better sports drink formula.

Copyright 2003 by Poweringmuscles. Published with permission. For cutting-edge sports nutrition info, visit www.poweringmuscles.com.


Matt Fitzgerald is the author of "Triathlete Magazine's Complete Triathlon Book." He coaches runners and triathletes online through Carmichael Training Systems (www.trainright.com).


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