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By Kate McSpadden

 September 16, 2006












How does exercise affect the body?? 

            Similar to our minds, muscles need energy in order to function, especially for long periods of time.  Muscles receive this fuel for exercise from three different sources in the body: glucose that is stored in the muscles, glycogen that is made in the liver and fat stored throughout the body. It is the body’s job to ensure that the glucose that the body uses for exercise and the glucose that the body generates remain in balance.  This process is controlled by hormones in our bodies that are released during exercise.  These hormones are kept stable by small amounts of insulin.  Insulin is able to stop blood glucose levels from rising above normal. (  After a long bout of exercise, an athlete’s muscles are depleted of glycogen, which needs to be replenished in order for soreness to decrease so that exercise can occur in the future.


What is the role of sport drink companies?

            Many years ago, there were studies that showed that carbohydrates helped to refuel muscles and re-hydrate athletes.  The evidence showed that carbohydrates help to speed the resynthesis of muscle glycogen, particularly after exercise.  Therefore, the primary reason for consuming a sports drink is to prevent dehydration.  This is done by replacing the fluid and electrolytes that are lost through sweat, as quickly as possible. (  However, more recently, many popular sport drink companies have decided to target a new audience.  As well as catering to the every-day exerciser, these companies also want to appeal to the elite or serious athlete.  These athletes believe that it is necessary to continually improve, and in order to do so they must constantly make changes to their routine and the products that they use.  Therefore, they are a very convenient target audience for sport drink companies.  Recently, a number of sport drink companies have decided to broaden their horizons by adding protein to their carbohydrate sport drinks. (,7120,s6-242-302--8011-0,00.html)


What protein–carbohydrate sport drinks are available?

What claims do these companies make?

Endurox R4:

- Contains a 4:1 ratio of carbohydrate to protein.                         

- Replenishes glycogen in muscles and stress after exercise.

- Decreases muscle-damage and stress after exercise.

- Reduces muscle soreness by 36%.

- Increases performance by up to 66%.

“Endurox R4 enables you to train harder and better the next day and everyday.”



- Contains a 4:1 ration of carbohydrates to protein

- Re-energizes muscles during exercise

- Helps muscles recover faster after exercise

- Increases endurance by 33% and recovery by 83%.

“Accelerade. It’s whats next.”  (

Gatorade Nutrition Shake

- Supplies 20g of protein

- For post-exercise only

- Aids in muscle recovery and glycogen replacement




What does the research show?

            It is often difficult for athletes to know what products will or will not help their particular sport or their particular body.  There is even more confusion when athletes are bombarded with advertisements that often look too good to be true.  However, there are a number of studies aimed to help the consumer.  Saunders et al.(2004), Ivy et al.(2003), and VanEssen et al. (2006) These studies tested the validity of the claims made by the protein-carbohydrate sport drinks above and the myriad of other information that can be found in sport magazines, newspapers and on the internet. 

            The three studies discussed below ask the same question: Does the addition of protein to carbohydrate sports drinks affect an athlete’s endurance during a period of intense exercise or their recovery after the event?

            Saunders et al. (2004) studied 15 cyclists during two rides that were separated by a 12-15 hour break.  This double-blinded study divided subjects into three different groups: one group consumed a protein-carbohydrate drink (CHO+P), the second group consumed a carbohydrate-only drink (CHO) and the third group was given a placebo drink that tasted identical with the other two.  All subjects consumed their drink every 15 minutes of exercise.  The exercise event was to cycle until exhaustion.  The purpose of studying the subjects during two separate rides was to compare the endurance between the first and second ride in order to judge the extent to which each subject recovered after the first ride.  The researchers hypothesized that the CHO+P drinkers would endure longer and recover faster than either of the other two groups.  Saunders and his colleagues also believed there would be a greater difference between the three groups of subjects during the second ride.

            The results proved the researchers’ hypothesis correct.  The subjects who consumed the CHO+P drinks rode 29% longer than the subjects who consumed only CHO. While in the second ride, the CHO+P drinkers rode 40% longer than the CHO drinkers.  The researchers also tested muscle damage after the first ride (through plasma CPK levels); which showed that there was 83% less muscle damage among the CHO+P drinkers, than the CHO drinkers.  Therefore, the researchers were able to conclude that carbohydrate-protein drinks improve athletes’ endurance and recovery.   While these results support the researchers’ hypotheses and could be beneficial for athletes, there were many confounding variables that were not taken into account.  The first possibly interfering variable is that the subjects that consumed CHO+P also consumed more calories which could have affected the results, especially the improvement of recovery.  Another confounding variable is that subjects rode until exhaustion which would not occur in a real competition.    

            The Saunders et al. study speculated that protein in the CHO+P drink helped insulin stimulation during exercise  since researchers found higher insulin levels after exercise in those that consumed CHO+P instead of only CHO.  Yet, these elevated insulin levels are not different between those whom consumed CHO+P and CHO during exercise. 

                   Figure 1                                                                       Figure 2

Graphic                         Graphic


FIGURE 1- Time to exhaustion during performance rides

FIGURE 2- Amount of muscle damage    


            One year earlier, Ivy et al. (2003) wanted to answer the same question.  He had his subjects sprint hard for as long as possible after his three different groups had consumed the three different drinks (CHO+P, CHO, and placebo).  However, this study had similar weaknesses with the Saunders study as well.  The subjects who consumed the CHO+P beverage, also had a greater caloric intake than those who consumed only CHO.     

            Ivy et al. Found that the subjects who consumed the CHO+P drinks were able to spring 36% longer than those who consumed only CHO drinks.  However, one again, the subjects who drank the CHO+P beverage consumed 25% more calories than the two other groups.  These confounding variables skew the results as to whether or not endurance is prolonged by protein.  However, in a previous study, Ivy et al. (2002) found that the addition of protein to an athlete’s diet after prolonged exercise increased the resynthesis of glycogen in muscles.  There results were very compelling.

            A third study, by VanEssen and Gibala (2006) asked the same question as the previous two studies, however discovered different results.  VanEssen et al. found two main faults in the research design of the previous two studies, and then contolled for these faults.  Unlike Saunders et al.(2004) and Ivy et al. (2003), VanEssen et al. did not use the “time –to-fatigue” test(Saunders et al., 2004) but rather each performance test was a fixed distance.  There were ten subjects who performed an 80-km time trial three separate times.  It was a double blinded study where the subjects were divided into three groups: one group consumed CHO+P, another consumed CHO and the third consumed a placebo.  A second weakness found in the previous studies was that the subjects consumed less than an optimal intake of carbohydrates.  VanEssen et al. ensure that their subjects consumed more liquid throughout the three time trials- one liter every hour.  This consumption is 18% higher than the rate of fluid consumed in Ivy et al. and 49% higher than that of Saunders et al. (VanEssen et al., 2006). 

            VanEssen and Gibala (2006) found that subjects who consumed CHO+P or only-CHO drinks were able to complete their time trial 4.4% faster than the subjects who were given a placebo.  However, there was no difference found between those subjects who consumed the CHO+P drink or the CHO drink.  While all three of the studies used the same ratio of protein to carbohydrate (adding 2% protein to 6% carbs) as the other two studies, the subjects in this study consumed 1 liter of their specific beverage every hour during exercise.  VanEssen et al. concluded that when athletes consume optimal carbohydrate during exercise, and compete in a trial that is similar to an athletic competition (a set distance), protein does not have an affect on their performance. 

                                                                   Figure 3



Figure 3- Time required to complete a simulated 80-km cycling time trial.  


            While the advertisements above are very persuasive and confident, the scientific research disagrees with many of their claims.  The first two studies that found that protein affects endurance contain too many confounding variables to accept these results as valid and reliable.  The third study that controlled for two of these variables found no difference between sport drinks with protein and those without protein.  Therefore, it is necessary that more research occurs in order to decide the affect that protein has on athletes during exercise.  The two studies that researched the effectiveness of protein after exercise found compelling evidence that protein has an effect.  While protein may not help you compete longer or faster, it can help you decrease muscle damage and soreness the next day.  However, the one over-arching conclusion one can make from the research is that it is too early to decide what protein in energy drinks can do for you. 





Burfoot, Amby.  Should Your Sports Drink Contain Protein?  2006. <,7120,s6-242-302--8011-0,00.html>


Burke, Edmund.  Why a Sports Drink Should Contain Protein. 2002.  <> 


Gallen, Ian. Diabetes and Exercies.  <>


Ivy, J. L., H.W. Goforth, B.W. Damon T.R. Mccauley, E.C. Parsons and T.B. Price. Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. J. Appl. Physiol. 93:1337-1344, 2002.


Ivy, J. L., P. T. Res, R. C. Sprague and M. O. Widzer.  Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity.  Int. J. Sport Nutr. Exerc. Met. 13:388-401, 2003.


VanEssen, M., Gibala, M. J. Failure of protein to improve time trial performance when added to a sports drink. Med. Sci. Sports Exerc. 38:1476-1483, 2006.  


Figure 1- SAUNDERS: Med Sci Sports Exerc, Volume 36(7).July 2004.1233-1238

Figure 2- SAUNDERS: Med Sci Sports Exerc, Volume 36(7).July 2004.1233-1238

Figure 3- VAN ESSEN: Med Sci Sports Exerc, Volume 38(8).August 2006.1476-1483


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