Thursday, December 30, 2010
Nutrition and Performance: A Look Back
The study followed the Oxford United team over the course of a season (40 matches). The pre-match routine for the entire season was to train to exhaustion on Thursday, light training on Friday followed by a high carbohydrate diet, and match play on Saturday. Prior to 20 matches, players were given a “glucose syrup” supplement. The other 20 matches served as the control. The supplement contained 420-450 kcal in about 250 ml (8 oz) with added mineral salts (remember a kcal is the same as a calorie on the product label). This solution contained about 9 times the amount of carbohydrates as a typical sports drink in a much more concentrated solution (hence the term “syrup”). This supplement was given 30 minute prior to the start of the match.
The results were quite remarkable, especially when looking at the second half of the match. When taking the glucose supplement prior to the match, the team scored 20 second period goals compared to only 10 goals when no supplement was taken. Also the team conceded only 3 second half goals with the supplement compared to 13 without. During the final 30 minutes, the number of scoring opportunities was more than double during the supplemented matches as opposed to the non-supplemented condition (~48 vs 20). Finally, the glucose syrup taken prior to kick-off helped the players maintain blood glucose levels during the match. Without the supplement, blood glucose tended to decline slightly.
The author of the paper concludes by emphasizing the importance of pre-match nutrition, “In general, exercise should be tapered off forty-eight hours before competitive effort, and the athlete should rest, taking a high carbohydrate diet. The last meal eaten should be light, high in carbohydrates and can be supplemented with glucose syrup thirty minutes before the event. In this way, individual and team performance can be improved, and a simple rational approach to sporting dietetics maintained”.
Granted, there are a few problems with the study. Control issues such as blinding to counter a placebo effect and randomization ensuring that the supplement wasn’t given before playing only weaker teams were not mentioned. Also, no information on the score line during the matches is provided. All of these could have easily affected the results. However, the author’s basic conclusion emphasizes the need for players to have a proper nutritional strategy.
The idea that a high carbohydrate diet and carbohydrate supplements can affect exercise performance can be traced back more than 70 years. In 1932, renowned exercise physiologist D.B. Dill of the Harvard Fatigue Lab fed his dog Joe candy and increased his exercise time from about 4 hours to more than 17. Glucose supplements improved exercise performance in humans as well. Scandinavian researchers showed in 1939 that 3-7 days on a high carbohydrate diet more than doubled exercise duration (80-210 minutes). In the 1970’s, U.S. and British researchers began to understand the benefits of carbohydrate loading - depleting the muscle of glycogen followed by eating a high carbohydrate meal (the approach used in Muckle's study). This early work on diet, carbohydrates and exercise eventually lead to the development of diet strategies as well as the explosion of the diet supplements such as Gatorade and PowerBar.
Given that this information has been available for nearly 80 years, it is surprising that many players don’t get the message that a high carbohydrate diet is optimal for performance. Several studies conducted over the past few years show that the soccer players diet is too high in fat and too low in carbohydrates. This is true for youth, collegiate and adult players as well as for males and females. The carbohydrate intake by most soccer players (youth through college and adult) is about 45% of their total calories. Fat occupies more than 35% of their calories. This is far from the recommended intake of 65% carbohydrate, 25% fat and 10% protein. Without adequate carbohydrates in the diet, muscles cannot replenish muscle glycogen. This, in turn will leave the athlete short of peak performance the following day.
Back to the original question, are today’s researchers learning anything new? On the one hand the answer is yes. We are developing a better understanding of the cellular, biochemical and psychological processes that link diet and exercise. We are beginning to understand how to “tweak” the diet for specific sports that have different energy demands and we are finding out that many traditional products can benefit performance (such as chocolate milk). On the other hand, the fundamental principles of using a high carbohydrate diet to improve performance haven’t changed since the 1930’s. Perhaps better education and communication are needed to convince athletes of the benefits of a carbohydrate rich diet.
Christensen EH, Hansen O (1939) Arbeitsfähigkeit und ernährung (Work capacity and nutrition). Scandinavian Archives of Physiology, 81:160-175.
Dill DB, Edwards HT, Talbott JH (1932) Studies in muscular activity, Journal of Physiology (London), 77:49-61
Muckle DS (1972) Glucose syrup ingestion and team performance in soccer, British Journal of Sports Medicine, 7:340-343.
Williams JH (2010) The SCIENCE of Soccer Online, Blurb Publishing.