The optimal type of carbohydrate (CHO) for a sports beverage partly depends on whether it will be used before, during or after an event.

“Dull headache, unusual weakness, uncoordination and breathlessness”: These are not physical characteristics any athlete wants to experience. However, they are a few of the symptoms of someone who is dehydrated, said Bob Murray, PhD, FACSM, director of the Gatorade Sports Science Institute, speaking at the 2005 Prepared Foods’ New Products Conference. Indeed, sports beverages’ rehydration benefit has made them one of the “healthiest” product categories in recent years.

Specific estimates on the market size of nutritional sports products vary depending on definitions used and data included. An October 2005 report by Mintel International, “The Market for Sports Food and Drinks,” placed category growth at 48% between 2000 and 2005. Category sales (excluding Wal-Mart) were estimated at $6.1 billion in 2005. Mintel noted that energy drinks drove growth as they added nearly 15 percentage points to their market.

Datamonitor figures for the same period estimate consumer spending on sport foods and beverages increased by 6.7% to reach $3.1 billion in the U.S. in 2005. This compares to a more modest 2.3% growth in sports nutrition supplements, which reached $621 million in sales. Within the food arena, “Sports bars are showing the biggest increase in sales growth, even though sports beverages have the highest sales,” says John Band, senior analyst at Datamonitor.

Evolving Formulations

Gatorade, arguably the most commercially successful sports beverage, was first introduced in 1967. Today, it has about an 80% market share in the U.S. and is sold in over 40 countries. Its 2005 (global) sales were over $3 billion, said Murray.

From its inception, Gatorade has contained three essential ingredients for athletes: carbohydrates (CHOs), minerals and water. Over the years, sports beverage formulations have evolved. Isotonic formulations have become popular. An isotonic solution has concentrations of minerals and certain other compounds similar to that of blood. However, these products do not always “sit well” when consumed after intense exercise. Hyptonic drinks that contain lower concentrations of metabolites have replaced them.

Recently, energy drinks with stimulants and products with proteins and peptides and more “exotic” ingredients like taurine, creatine, chromium and L-carnitine have entered the marketplace. Interest in antioxidants also is on the rise.

While low-sodium, “low-glycemic index,” non-digestable CHO and simple or “clean labels” are formulation goals for many foods, enhanced sports performance products often use significant amounts of sodium, insulin-releasing CHOs and, at times, “technical-sounding” ingredients. What are the theories behind these ingredient systems, and what is on the horizon?

Research shows that carbohydrate (CHO) metabolism differs between men and women athletes. PHOTO COURTESY OF BAZIL RAUBACH

Rehydration Redux

Couch potatoes and weekend warriors alike have reached for Gatorade on a sweltering day with the belief that it was just what they needed. Perhaps a testimony to Americans’ awareness of sports drinks’ ability to rehydrate is the statistic that the South accounted for nearly 45% of all sports beverage wholesale dollars in 2005, according to the Beverage Marketing Corporation. The West followed with some 25%, the Midwest at 17% and the Northeast at about 13%.

“Whenever vigorous physical activity occurs—and especially when it occurs in a warm environment—cardiovascular and thermoregulatory functions are placed under severe stress,” notes Murray in his paper, “Preventing Dehydration: Sports Drinks or Water.” It is posted on the Gatorade Sports Science Institute website ( As muscles (including heart muscle) and skin compete for a limited blood supply, the body’s cardiovascular capacity to cope can be quickly exceeded. Even slight dehydration such as a 1% to 2% loss in body weight has a negative effect on physiological function and performance.

Current fluid replacement guidelines recommend a goal of replacing 100% of sweat loss during exercise. However, there are a number of challenges to maintaining proper rehydration. Murray notes that the human thirst mechanism is an inaccurate short-term indicator of fluid needs. And profusely sweating athletes (over 2L/hr) may not be able to ingest enough fluid to remain completely hydrated. A properly formulated sports drink provides benefits over other options. He writes that four key goals of such drinks are as follows:
  • Encourage voluntary fluid intake. When water is lost through sweat, the blood’s sodium concentration increases, and total blood volume decreases. Both situations drive thirst. Water will lower the blood’s sodium concentration, satisfying thirst before a body is completely hydrated. Therefore, it is important that sports drinks be formulated to maintain the drive to drink until the person is fully rehydrated.
  • Stimulate fast absorption. Desired goals are to maximize gastric emptying and speed water, CHO and electrolyte absorption into the blood. Carbonated beverages or those with high CHO levels tend to slow gastric emptying and/or cause gastric distress during exercise. Large volumes of food and foods or beverages with a high energy (calorie) content primarily slow gastric emptying; however, intense exercise slows emptying as well.
    A product’s osmolality is also a factor. The surface of the jejunum of the proximal small intestine is rich in protein receptors that allow sodium and glucose into the cell. As a result of the transport of these compounds, water molecules quickly follow to maintain osmotic equilibrium. “Too much carbohydrate, the wrong types of carbohydrate, or too high an osmolality will slow fluid absorption,” writes Murray.
  • Promote rapid and complete rehydration. Because electrolytes are lost in sweat, electrolytes are needed in rehydration beverages at amounts that will help a body maintain plasma sodium levels; additionally, they serve as an osmotic impetus to retain ingested fluid by reducing kidney urine production.
  • Improve performance. Maintaining blood glucose levels and promoting muscle cell carbohydrate uptake increases brain and muscle tissue use of CHOs for fuel. Thus, sustaining CHO oxidation helps performance in a variety of ways, including maintaining motor skills.

High Glycemic Goals

It is common for athletes to “top off” or “carbo load” before an endurance event in order to maximize glycogen storage in muscle tissue and delay the onset of fatigue. “The ‘classic’ regimen generally includes an intense glycogen-depleting training period of approximately two days followed by a glycogen-loading period for 3 to 4 days, ingesting approximately 60% to 70% of total energy intake as carbohydrates, while the newer method does not consist of an intense glycogen-depletion protocol,” write Jennifer Wismann and Darryn Willoughby in a research review on gender influences in CHO metabolism. (See sidebar “Carbohydrate Metabolism and Sex.”)

It is well known that muscle cells use glycogen as their predominant energy source during exercise. Thus it is important for athletes to maximize glycogen stores. For athletes undergoing continuous exercise or multiple, closely spaced workouts, glycogen stores need to be quickly replenished. Restoring glycogen stores is also important post-exercise to promote a faster recovery.

CHO consumption is a key tactic in managing glycogen storage. However, the types of CHO and timing of ingestion is a complicated topic. For example, depending on many factors, not the least of which is their molecular structure, CHO range from being rapidly digestible to non-digestable.

Glycemic index (GI) refers to a food’s ability to increase blood glucose levels which, in turn, triggers an increase in insulin levels. Products with a moderate to low GI or, more accurately, those that will more evenly sustain blood glucose release and maintain fat oxidation, are thought to spare muscle glycogen. Consuming high-GI products less than an hour prior to an athletic event may result in low blood sugar (hypoglycemia) at the start of the event. Adding dietary fiber, especially soluble fibers, protein and fat, lowers GI.

It is sometimes stated that “simple” sugars are for quick energy and “complex carbohydrates” are for slower, sustained energy. However, this is an oversimplification. For example, fructose is a simple sugar that the body absorbs and metabolizes relatively slowly compared to glucose. Isomaltulose, described in a press release as “the first slowly digestible sugar resulting in a low blood glucose and insulin response for sports beverages,” was recently launched. On the other hand, more complex CHOs in the form of maltodextrins have a higher GI more similar to glucose.

Formulating pre-event sports products and foods to deliver a subdued insulin response is, in general, a proper goal. Thus, it seems counter-intuitive that ingredient systems that increase insulin levels could be beneficial as well. Athletes generally are advised to ingest products with a high GI during and immediately after athletic events. Muscles require readily available (quick) energy during intense exercise. In this case, hypoglycemia from insulin spikes is less of an issue since insulin release is, in effect, down-regulated during exercise.

Gatorade Endurance Formula is a new specialized sports drink for athletes undergoing longer and more intense exercise occasions, when fluid and electrolyte losses can be very significant.

Profiting from Proteins

The issue of CHO intake becomes yet more complex when considered in combination with peptides and proteins. For example, one study (van Hall, G, et al., 2000. J Appl Physiol, p 1631) found additional ingested protein had no effect on muscle glycogen resynthesis during recovery from cycling exercise, while another (Burke, L, et al. 2004. J Sports Sci, p 15) recommended that consuming protein after an event “may promote additional glycogen recovery when CHO intake is suboptimal or when frequent snacking is not possible.” Other researchers also find positive results. They include both older studies, such as those describing the benefits of protein in a paper entitled “Carbohydrate-protein Complex Increases the Rate of Muscle Glycogen Storage After Exercise” (Zawadzki, KM et al., 1992. J Appl Physiol, p 1854), as well as more recent ones. Two widely-quoted papers supporting their performance benefits include “Effect of a Carbohydrate-protein Supplement on Endurance Performance During Exercise of Varying Intensity (Ivy JL, et al., 2003. Int J Sports Nutr Exerc Metab, p 382) and “Effects of a Carbohydrate-protein Beverage on Cycling Endurance and Muscle Damage” (Saunders MJ, et al., 2004. Med Sci Sports Exerc, p 1233).

Protein benefits go beyond their role in recovery. Amino acids, peptides (short chains of amino acids) and proteins (long chains of amino acids) assist with muscle growth and also repair post-exercise damage. “Whey protein helps maintain and build new muscle mass,” maintains Tia Rains, PhD, DMI nutrition consultant and adjunct faculty member, Rosalind Franklin University. Clinical studies have shown that whey proteins independently stimulate muscle protein synthesis; stimulate protein synthesis better than carbohydrates alone and also augment new muscle protein after resistance exercise, she adds.

The ideal amino acid, peptide and protein choice for sports nutrition is still under investigation, but essential amino acids are considered more useful than non-essential for encouraging muscle growth. For example, tryptophan, arginine and the branched-chain amino acids of leucine, isoleucine and valine often are used. Individual studies provide intriguing results, but each in itself does not provide definitive answers. Researchers of one study (Kerksick, CM, et al., 2006. J Strength Cond Res., p 643) found that a combination of whey and casein protein promoted greater increases in fat-free mass after 10 weeks of heavy resistance training as compared to a placebo or a combination of whey, branched-chain amino acids and L-glutamine.

Formulators face challenges when working with amino acids and peptides, as they are often bitter. The supplier industry has developed peptides with better-tasting characteristics, and they are on the market.

Ergogenic Aids

Even as controversial ephedra fades from the sports scene, another unlikely stimulant, caffeine, is taking its place both for functionality and controversy. The Coffee Science Information Center website notes that caffeine is widely reported to be an ergogenic aid.

Caffeinated beverages attract consumers for whom receiving an energy boost is by far the most important motivation to purchasing a sports product, says Band. “It is no longer profitable to provide advantages to only serious athletes. As such, it would be prudent for companies to catch the attention of the mainstream consumer by targeting specific health benefits that will tie into existing sports benefits,” he adds.

However, criticism is being leveled at products providing high amounts of caffeine and caffeine-related compounds including those from non-coffee sources such as guarana and yerba maté. The Chicago Tribune reports that, according to Simmons Research, some 500 new energy drinks were launched in 2006 (including a controversial one named Cocaine Energy Drink) and that 31% of U.S. teenagers drink them. Michael Wahl, managing medical director for the Illinois Poison Center, was quoted saying, “Caffeine is a stimulant that releases your internal catecholamines (compounds that can serve as hormones) that make you anxious, jittery and create the fight-or-flight response. When the heart beats too fast, bad things happen. It’s an emerging trend to keep an eye on and see if it’s getting worse.” Additionally, caffeine’s role in serious sports drinks is questionable in that some believe that since it is a diuretic, it counteracts the benefits of hydration.

Marketing products to both mainstream consumers and the serious athlete is difficult. Some athletes have been “put off” from drinking certain popular sports beverages since everyone drinks them. Supposedly in response, Gatorade released Gatorade Endurance, which is tailored to meet the needs of serious athletes. Perhaps PepsiCo can have the best of both worlds. “Companies need to target the variants of sports needs like endurance, hydration, muscle building and so on,” says Band. Doing so will increase credibility with athletes without alienating the mainstream consumer. The result will require sports performance formulations that include specific ingredients for specific needs.

Sidebar: Carbohydrate Metabolism and Sex

In Wismann’s and Willoughby’s research review, they note that hormonal differences produce metabolic differences and that the hormone estradiol is linked to enzymes that have a role in energy metabolism. One study indicated that females appeared to have an enhanced sensitivity to insulin in skeletal muscle, which would theoretically result in increased muscle glycogen storage. Various studies suggest that differences in CHO and skeletal muscle glycogen metabolism are due to triglyceride utilization. “Therefore, for a female to carbohydrate load and achieve benefits comparable to those of a male, the female must consume extra calories rather than simply [increase] the percentage of dietary carbohydrate load,” they wrote. “Despite many questions that remain to be answered in regards to gender differences in carbohydrate metabolism during endurance exercise, it appears as though female athletes do have the capacity for glycogen super-compensation at levels comparable to males when fed comparable amounts of carbohydrates relative to lean body mass,” they conclude.

Source: Wismann, J and D Willoughby, 2006. JISSN, p 28


Sidebar: An Elixir of Energy

South Beach’s No Fear energy drink, introduced in the U.S. in 2003 and more recently by Pepsi-Cola into the Canadian market, is an elixir of caffeine-containing ingredients, antioxidants and other compounds that have been researched for their ability to enhance performance. Its contents include 100% of the Daily Value (DV) for folic acid and vitamin C, B6 and B12, as well as 25% of the DV for selenium and 10% for zinc. Its website notes it also contains 1,000mg of taurine, 100mg of inositol, 50g each of Panax ginseng and guarana (Paullinia cupana) seed extract, and 25mg each of grape seed extract and L-carnitine. Caffeine, L-arginine, L-methonine and soy protein isolate also are listed on the ingredient legend.

Website Resources— Type in “science of stamina" or “glycemic index” in the search field for more information on those subjects— Research can be found at the Gatorade Sports Science Institute— Discussion of antioxidant requirements in trained athletes and weekend warriors— Food and beverage industry market research— Glossary of ingredients in its products— Contains abstracts with sports products statistics— The Coffee Science Information Center on caffeine and sports— The American College of Sports Medicine organization