Introduction

Energy drinks are a rapidly growing category of the Australian soft drink market. There is now a wide range of energy drinks available in Australia. A recent Australian survey found that some teenagers were drinking up to five cans a day before sporting events in the belief that they will boost sports performance.

In addition to carbohydrate, these drinks also contain a variety of other ingredients including amino acids, vitamins, minerals and herbs. Most also contain caffeine or guarana (a herbal source of caffeine) at a level similar to or slightly greater than a cup of instant coffee (Table 1).

Energy Drinks are NOT Sports Drinks!

A number of energy drinks are now marketed as 'sports energy drinks'. Although this term suggests that energy drinks are beneficial for exercise or sports performance, their composition is diverse and at the current time none of those sold in Australia meet Australian or International guidelines for sports (electrolyte) drinks. (2,3). An ideal sports drinks has three important criteria - carbohydrates, electrolytes and no carbonation. Using these criteria energy drinks are judged below.

Carbohydrates

The amount of carbohydrate present in energy drinks (e.g. 10-12%) is similar to soft drinks and is much higher than sports drinks (usually 6-8%). Australian and international guidelines for optimal fluid replacement recommend beverages have an absolute maximum of 8% carbohydrate as levels greater than this delay stomach emptying and increase the risk for dehydration and gastrointestinal upset during exercise. Gatorade has an optimum level of 6% (4) (Table 1).

Electrolytes

Sodium is an important electrolyte in sports drinks as it helps to optimise hydration and maintain thirst drive. Sodium also has a role in preventing low levels of sodium in the blood (hyponatremia) which may occur during prolonged exercise in the heat and is potentially life threatening. Energy drinks have either too little sodium or too much (3) (Table 1). Where as sports drinks are formulated with the right mix of carbohydrates and sodium for optimal hydration and taste.

Carbonation

Most energy drinks are carbonated while sports drinks are still. Studies have shown a trend that carbonation increases the risk for gastrointestinal discomfort during exercise (5).

Caffeine and Guarana

Energy drinks, unlike sports drinks contain varying amounts of caffeine or guarana. Caffeine levels range between 30 to 80 mg per serve which is comparable to 1-2 cans of cola or 1-2 cups instant coffee. Caffeine, a diuretic, increases urine production and elevates the risk of dehydration. Caffeine containing beverages are therefore unsuitable as rehydration fluids for use before, during of after exercise.

The International Olympic Committee (IOC) classifies caffeine as a restricted substance. Urine caffeine levels greater than 12 mg/ml are deemed 'positive' and athletes with such levels may be sanctioned or banned from competition. (6) Unfortunately the caffeine content of energy drinks is often not disclosed on the label and athletes may not be aware that guarana is another source of caffeine.

Vitamins and other functional ingredients

Energy drinks may also contain a wide range of other ingredients. Many of these are vitamins, particularly vitamin A and some of the B group vitamins (B2, B3, B5, B6 and B12). Although vitamin supplementation remains popular in Australia, there is no evidence of benefit in healthy individuals or athletes who are not vitamin deficient. Consumption of two servings of some energy drinks may also exceed the recommended safe daily intake of vitamin A and niacin-B3, particularly for children (1). In addition to vitamins, energy drinks typically contain a range of functional ingredients (Table 2) however there is no scientific evidence of performance benefits.

Table 1
Functional Ingredients found in Australian Energy Drinks

The Role of Energy Drinks

Healthy adults can include energy drinks in a balanced diet, as a "pick me up" like coffee, if taken in moderation. The concern is that energy drinks may be over-consumed or mistaken for sports drinks or soft drinks by consumers.

The Role of Sports Drinks

Sports drinks are specifically formulated to enhance hydration and optimise sports performance. Studies support the performance enhancing benefit of sports drinks for exercise lasting anywhere from 30 minutes in duration (7). Consumption of sports drinks post exercise also promotes rehydration and glycogen replenishment.

Fluid requirements before, during and after exercise

Each individual needs to determine their fluid losses and drink enough to meet their needs. Sweat rates vary from approximately 250 ml to two or more litres per hour in hot weather. Fluid requirements can be individualised by:

• Weighing in minimal clothing pre and post-exercise. Every kilogram lost is equivalent to 1 litre of sweat. Aim to replace at least 80-100% of fluid loss during exercise.
• Post-exercise consume 1.5 times fluid loss to ensure the hydration process is complete.
• Start exercise well hydrated. Drink approximately 300-500 ml approximately 30 minutes before exercise.

Energy Drinks: What Coaches Should Know

• Carbohydrate contents of energy drinks are too high to promote optimal fluid replacement during exercise and may result in dehydration or gastrointestinal upset.
• Carbonation in energy drinks may contribute to the risk of stomach upset if consumed during exercise.
• Energy drinks have either too little sodium or too much. Where as sports drinks are formulated with the right mix of carbohydrates and sodium for optimal hydration and taste.
• There is no convincing evidence that vitamins or other functional ingredients in energy drinks enhance exercise performance.
• Caffeine or guarana in some energy drinks may compromise hydration and increase the risk for a positive drug test. Excessive consumption may also pose a health risk.

Table 2
Nutrient comparison of the sports drink Gatorade and selected energy drinks

All Champs Tennis Academy thanks GATORADE for granting permission for the use of this article. Also thanks to The Coaches Edge at www.coachesedge.com.au

References

1. Souped-up Fizzy Drinks. Choice magazine August 2001 pp23-27.

2. Sports Dietitians Australia (1998). Consensus Statement on Fluid and Energy Replacement For Exercise and Sports Activities

3. American College of Sports Medicine. Position stand on exercise and fluid replacement. Med Sci Sports Exerc 1998;28:i-vii.

4. Murray R, Bartolli W, Stofan J, Horn M, Eddy D. A comparison of the gastric emptying characteristics of selected sports drinks. Int J Sport Nutr 1999;9(3):263-74

5. Zachwieja JJ, Costill DL, Beard GC, Robergs RA, Pascoe DD, Anderson DE. The effects of a carbonated carbohydrate drink on gastric emptying gastrointestinal distress and exercise performance. Int J Sport Nutr 1992 2;239-50.

6. IOC List of Prohibited substances www.wada-ama.org/asiakas/003/wada_english.nsf/Home?OpenPage

7. Ryan M. Sports drinks: Research asks for reevaluation of current recommendations. JADA 1997; 97 (suppl 2):S197-S198.