Gatorade® appeared in the mid-1960s and launched the sports drink market in the US. Today, sports drinks are big business. On store shelves you can find not only sports drinks, but, also, energy drinks, recovery drinks, fitness water, energy gels, and probably others.

The following discussion will review sports drinks. I will also summarize some research on the newest category of sports beverages, sometimes called "recovery" drinks. "Energy" drinks, a very non-specific term, are discussed in a separate review (see "Energy Drinks").

WHAT IS A SPORTS DRINK?

There is no universally-accepted description or criteria for what constitutes a sports drink. In general, sports drinks supply 3 categories of substances:

• fluids (eg., water)
• electrolytes (eg., sodium, potassium, others)
• carbohydrates (eg., fructose, glucose, maltodextrin, sucrose)

According to Robert Murray, PhD, Director of the Gatorade Sports Science Institute, the European Union defines sports drinks as beverages that contain carbohydrate in a concentration range of 2.0 - 8.75%, with an osmolality of less than 400 mOsm. Gatorade® and the other "first generation" of sports rehydration beverages on the market today contain a combination of several carbohydrates with several electrolytes.

SPORTS DRINKS vs. WATER

Amazingly, up until 1969, athletes were discouraged from consuming fluids while running. It was thought that drinking fluids would impair athletic performance. Since then, hundreds of scientific studies have examined every aspect of these beverages on athletic performance. Today we know that athletic performance falls as an athlete loses fluids (Armstrong LE, et al. 1985).

When Robert Cade, MD, invented Gatorade® at the University of Florida, the goal was to find a better way to hydrate college athletes who were perspiring heavily in the hot Florida sun. But, despite their popularity, are sports drinks like Gatorade® any better than plain water?

It turns out that water by itself is not the best rehydration beverage during strenuous activities. Drinking plain water shuts down the sensation of thirst too quickly. Many athletes stop drinking too soon. When Puerto Rican soccer players were left to drink plain water on their own, they were still significantly dehydrated (Leiper JB, et al. 2001). A thirsty person drinks more fluid when the beverage contains sodium (and flavoring) compared to plain water.

Obviously, the easiest way to correct this is to get athletes to drink more water, however this can backfire. Drinking too much plain water can lead to hyponatremia, a serious medical condition where the concentration of sodium in the blood gets too low. This has been documented in marathon runners (Almond CSD, et al. 2005) and in soldiers during training. In rare cases, hyponatremia can be fatal (Ayus JC, et al. 2000).

SPORTS DRINKS: Sodium Content

In the last several years, the sports medicine community changed its stance on hydration. No longer are athletes told to "drink as much as you can". Now, the amount of fluid that is recommended is more moderate. Also, taking in sodium has become much more important. (See the related story: "Fluids and Electrolytes During Exercise".)

Sports drinks contain varying amounts of sodium, along with other electrolytes. As discussed above, the addition of sodium not only helps to prevent the development of hyponatremia, but also encourages an athlete to drink more.

Thus, because sports drinks contain sodium, they are a better choice than plain water when perspiring heavily.

According to Murray, the optimum concentration of sodium in a sports rehydration drink is 20-40 mmol/liter. On the label, this would be expressed as: 110 - 220 mg per 8 fl. oz. The sodium content of several products is listed below.

SPORTS DRINKS: Carbohydrate Content

While rehydration continues to be a major reason to consume sports drinks, it is their ability to furnish rapidly-absorbed carbohydrates that is arguably even more important. Hundreds of research studies over the past 3 decades have proven that ingesting carbohydrates during prolonged strenuous exercise enhances performance compared to plain water (Hawley JA, et al. 1992). In other words, sports drinks serve 2 roles: (a) rehydration and (b) fuel for exercising muscles.

Research shows that, when the carbohydrate concentration in a beverage increases above 8%, gastric emptying slows (Mitchell JB, et al. 1989) (Murray R, et al. 1999). This is a critical factor in the development of sports drinks since strenuous exercise by itself can impair gastric emptying: as exercise intensity increases, the rate of gastric emptying decreases (Moodley D, et al. 1992; Leiper JB, et al. 2001). Thus, if you drink beverages with a carbohydrate concentration greater than 8% while running, not only does this impair the delivery of fuel to exercising muscles, you may be more likely to develop GI intolerance (stomach cramps, vomiting).

According to Murray, the optimum concentration of carbohydrate in a sports drink is 6-8%. This concentration can also be expressed as:

• 6 - 8 grams per 100 ml
• 14.2 - 18.9 grams per 8 oz.
• 21.3 - 28.4 grams per 12 oz.

Gatorade Thirst Quencher® and Gatorade Endurance Formula® both contain 14 grams of carbohydrate per 8 oz serving (source: product labels, July 2006). This equals a 5.8% solution. By comparison, fruit juices contain roughly 10% carbohydrate and soft drinks contain 10-12% carbohydrate.

Further, it has been shown that absorption and oxidation of carbohydrates during strenuous exercise is optimized if carbs are supplied in a mixture of several types, as opposed to a single carbohydrate source (Jentjens RL, et al. 2004a; 2004b). The carbohydrates in Gatorade® come from a mixture of sucrose syrup and glucose-fructose syrup.

Protein-Free Sports Drinks:

Listed below are some of the more popular sports drinks that do NOT contain protein or amino acids (quantities listed are per 8 oz serving of the ready-to-drink product unless otherwise noted):

**Because Gatorade Performance Series contains such a high concentration of carbs, it should be limited to post-race consumption to replenish muscle glycogen, or well before a race for carbo-loading. The other products are suitable for consumption during competition.

SPORTS DRINKS: Protein Content

Just as carbohydrate-containing sports drinks are superior to plain water for improving performance, it now appears that sports drinks that contain a mixture of carbs+protein (aka: "recovery" drinks) have advantages over the traditional carbohydrate-only types. Carb+protein drinks appear to be more efficient at increasing both muscle glycogen (Zawadzki KM, et al. 1992) and muscle protein (Miller SL, et al. 2003) after strenuous exercise.

Several studies show that exercise performance is better in athletes who consume carb+protein beverages compared to athletes who received the carbohydrate-only type (Ivy JL, et al. 2003) (Saunders MJ, et al. 2004).

However, these studies have been criticized on the fact that more total calories were given to the group receiving the carb+protein formula. Saunders et al. (2004) counter that argument by pointing out that the athletes more than offset these extra calories in the amount of effort expended during the carb+protein phase of the study.

Further, muscle injury and/or soreness may be less when protein is ingested after strenuous exercise. Several studies show that CPK levels (a marker for muscle injury) are lower if a combination of carb+protein is consumed immediately following exercise. Marine recruits who received protein supplementation immediately postexercise had less muscle soreness (Flakoll PJ, et al. 2004).

So, even if these newer carb+protein drinks don't improve performance over the traditional carbohydrate-only-type beverages, they may have another claim to fame: more rapid muscle recovery (hence the name "recovery" drinks).

Some of these products are listed below:

Protein-Containing Sports Drinks (amounts listed are per 8 oz serving):

So, does the emergence of these new carb+protein sports drinks signal the end of the reign of Gatorade®? Robert Murray, PhD, doesn't think so. He is not convinced that the studies published to date are adequate to answer the question. Interestingly, the Gatorade Company has released several new variations on its original "Thirst Quencher" product (eg., "Gatorade Endurance Formula", "Gatorade Performance Series Energy Drink"). Although none of these 3 products contain protein or amino acids, you can bet they are keeping a close eye on this new research.

CAFFEINE-BASED ENERGY DRINKS (ex: Red Bull®)

At this point, you may be asking, "aren't 'energy' drinks and 'sports' drinks just different names for the same category of beverage?"

No. Energy drinks and sports drinks are clearly different, though, admittedly, there is quite a bit of overlap. For example, Gatorade calls its Performance Series sports beverage an "energy drink" and the tag-line on Powerade's® label is currently "liquid hydration + energy drink". However, these beverages contain the desired concentration of carbs and no caffeine, so I grouped them with the sports drinks listed above.

Generally, beverages categorized as energy drinks contain a lot of caffeine (or herbal sources of caffeine), a high carbohydrate concentration, and not much else. One of the most popular products on the market in this category is Red Bull®.

The carbohydrate concentration of almost all energy drinks is typically much higher than the sports drinks described above (Gatorade Performance Series being an exception). The carbohydrate concentration of most energy drinks ranges 11-15%, making them unsuitable for consumption during competition. Thus, energy drinks are not much different than soft drinks such as Coca-Cola® or Mountain Dew®, except for the fact that other substances such as herbs, amino acids, and vitamins are sometimes thrown in.

Also confusing is Arizona Beverage's "Low Carb Extreme Energy Shot". Its carbohydrate concentration is only 1.25%. Even though it doesn't violate the rule "carbohydrate concentration in sports drinks should be no higher than 8%", it is clearly an energy drink, not a sports drink.

It's important that athletes can differentiate caffeine-based energy drinks from true sports drinks. The ideal sports drink contains a proper amount of carbs and electrolytes with, generally, no caffeine and no vitamins. Energy drinks are reviewed in detail in another story (see Energy Drinks).

QUESTIONS

Q: What about glycerol?

ANSWER: Glycerol occurs naturally in the body. It has been used IV and orally in clinical medicine and has been studied in athletes for more than 25 years because of its ability to retain body water. During exercise in hot climates, glycerol helps to regulate body temperature (Robergs RA, et al. 1998).

But the real question is: does glycerol have any effects on exercise performance? Several studies have been done, but the results vary. Glycerol improved performance during cycling (Anderson MJ, et al. 2001) (Montner P, et al. 1996) and mountain biking (Wingo JE, et al. 2004), but was not helpful in tennis players (Magal M, et al. 2003) or triathletes (Inder WJ, et al. 1998). The dose employed in these studies was similar (generally in the range of 1.0-1.2 g/kg).

Before trying it, athletes need to keep 2 things in mind: Glycerol can cause GI intolerance. This is important because it has a short half-life, and, therefore, must be ingested just prior to competition. Also, at one time, the USOC considered glycerol a banned substance (it was classified as a diuretic). This ruling was changed in 1997, but other sports organizations may restrict it. WADA and NCAA ban diuretics, but do not specifically mention glycerol on their 2005 lists. Nevertheless, investigate it before you use it in competition.

SUMMARY AND RECOMMENDATIONS

Let's summarize what to look for when selecting a sports drink:

•Sodium: It is very important that athletes who are perspiring heavily, or, over a prolonged period of time (eg., marathon walkers), take in sodium. All sports drinks contain some sodium. The optimum concentration of sodium in a sports drink is 20-40 mmol/L. On the label, look for:

• 110 - 220 mg per 8 oz serving

This amount of sodium is not harmful....sports drinks contain much less sodium than foods like cheeseburgers, fries, and potato chips. If plain water is the only liquid available during a race, then try to eat some salty pretzels during and after the event.

• Carbohydrates: Taking in carbohydrates while exercising or competing is now universally accepted as beneficial. According to most sports nutritionists, the optimum "dose" is 30-100 grams per hour during a lengthy race. If you use a sports drink, look for one with a carbohydrate concentration of 4-6%. If you mix your own from powder, make sure the concentration is not more than 8% in order to avoid GI distress during your race.

• Carbohydrate-only sports drinks vs. carb+protein sports drinks: Personally, I feel that as long as the carb+protein sports drinks don't cause GI intolerance, they should be considered. Research does show that the carb+protein drinks may have an advantage over sports drinks that do not contain protein. Ignoring the criticisms regarding study design, these beverages may enhance recovery even if they don't improve performance. But, as with anything else, test it during a training run before using it during a race to see if it agrees with your GI tract. Products with a carb concentration of >8% (for example, Endurox R-4®) should be limited to post-race consumption to avoid GI distress.

• Caffeine: If you don't want a sports drink with caffeine, then simply avoid those. Most sports drinks don't contain caffeine, so you have plenty of choices. "Caffeine" has to be listed on the label, but you must also watch for herbal sources of caffeine, such as "guarana". Guarana contains 3-6% caffeine. That's much higher than the amount in coffee beans (1-2%) or dried tea leaves (1-4%).

FOR MORE INFORMATION

Several web sites offer excellent information on sports drinks:

•The Gatorade® Sports Science Institute: www.gssiweb.com.

•The web site for Accelerade® and Endurox R-4® also contains some good information: www.Accelerade.com.

•An interesting web site that reviews beverages from a commercial perspective is: www.bevnet.com. Here, you can read short reviews of beverages and look up ingredients, though, for some products, a more comprehensive ingredient list was found on the manufacturer's product-specific site.

A good text on sports drinks was written by Robert Murray, PhD, and Ron Maughan (University Medical School, Aberdeen, Scotland): Sports Drinks - Basic Science and Practical Aspects (CRC Press, 2001).

Readers may be interested in these related stories:

• Fluid Requirements for Healthy Adults
• Fluids and Electrolytes During Exercise
• Fructose:  Public Enemy #1?
  

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ABOUT THE AUTHOR

Stan Reents, PharmD, is a former healthcare professional. He holds Personal Trainer and Lifestyle Counselor certifications from the American Council on Exercise and has been certified as a tennis coach by USTA. He is the author of Sport and Exercise Pharmacology (published by Human Kinetics).  He can be reached at: Editor@athleteinme.com.