Sports Nutrition – From Lab to Kitchen
Supported by:
Asker Jeukendrup (Ed.)
Meyer & Meyer Sport
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Asker Jeukendrup (Ed.)
Sports Nutrition – From Lab to Kitchen
Maidenhead: Meyer & Meyer Sport (UK) Ltd., 2010
ISBN 978-1-84126-915-3
All rights reserved, especially the right to copy and distribute, including the translation rights. No part of this work may be reproduced – including by photocopy, microfilm or any other means – processed, stored electronically, copied or distributed in any form whatsoever without the written permission of the publisher.
© 2010 Meyer & Meyer Sport (UK) Ltd.
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Editing: Martha Tuninga
ISBN 978-1-84126-915-3
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Authors
Chapter 01 | The history of sports nutrition |
Bengt Saltin and Asker Jeukendrup |
Chapter 02 | What is the optimal composition of an athlete’s diet? |
Liz Broad and Greg Cox |
Chapter 03 | The optimal pre-competition meal |
Asker Jeukendrup |
Chapter 04 | Carbohydrate intake during exercise |
Asker Jeukendrup |
Chapter 05 | Hydration: what is new? |
Asker Jeukendrup |
Chapter 06 | Fat burning |
Asker Jeukendrup |
Chapter 07 | Nutrition for recovery |
Louise Burke |
Chapter 08 | Nutrition, Sleep and recovery |
Shona Halson |
Chapter 09 | Building muscle |
Stuart Phillips and Mark Tarnopolsky |
Chapter 10 | Train low – compete high |
Keith Baar |
Chapter 11 | Optimizing training adaptations by manipulating protein |
Kevin Tipton |
Chapter 12 | Alternative fuels |
Asker Jeukendrup |
Chapter 13 | Dietary supplements |
Hans Braun |
Chapter 14 | Risks associated with dietry supplement use |
Ronhald Maughan |
Chapter 15 | Nutrition and immune function |
Michael Gleeson |
Chapter 16 | Supplements to boost immune function |
David Nieman |
Chapter 17 | Sports nutrition for women |
Brent Ruby |
Chapter 18 | Nutrition, the brain and prolonged exercise |
Romain Meeusen and Phil Watson |
Chapter 19 | Weight management |
Asker Jeukendrup |
Chapter 20 | Protein and weight loss |
Samuel Mettler and Kevin Tipton |
Chapter 21 | Nutrition- and exercise-associated gastrointestinal problems |
Beate Pfeiffer |
Chapter 22 | Marathon running |
John Hawley |
Chapter 23 | Nutrition for middle distance running |
Trent Stellingwerff |
Chapter 24 | Swimming |
Louise Burke |
Chapter 25 | Triathlon |
Asker Jeukendrup |
Chapter 26 | Adventure racing and ultra marathons |
Mark Tarnopolsky |
Chapter 27 | Team sports |
Stuart Phillips |
Chapter 28 | The Future: Individualizing nutrition & hydration |
Trent Stellingwerff |
References
Photo & Illustration Credits
Keith Baar
Department of Neurobiology, Physiology and Behavior, University of California, Davis, USA
Hans Braun
Sport Nutrition Department, Institute of Biochemistry, German Sport University Cologne, Germany
Elizabeth Broad
Sports Nutrition, Australian Institute of Sport, Belconnen, Australia
Louise Burke
Sports Nutrition, Australian Institute of Sport, Belconnen, Australia
Greg Cox
Sports Nutrition, Australian Institute of Sport, Belconnen, Australia
Michael Gleeson
School of Sport, Exercise and Health Sciences, Loughborough University, United Kingdom
Shona L Halson
Department of Physiology, Australian Institute of Sport, Belconnen, Australia
John Hawley
School of Medical Sciences, RMIT University, Bundoora, Australia
Asker Jeukendrup
School of Sport and Exercise Sciences, University of Birmingham, United Kingdom
Ronald Maughan
School of Sport, Exercise and Health Sciences, Loughborough University, United Kingdom
Romain Meeusen
Human Physiology & Sports Medicine, Free University Brussels, Belgium
Samuel Mettler
ETH Zurich and Swiss Federal Institute of Sport Magglingen, Switzerland
David C. Nieman
Director, Human Performance Labs, North Carolina Research Campus and Appalachian State University, Boone, NC, USA
Beate Pfeiffer
School of Sport and Exercise Sciences, University of Birmingham, United Kingdom
Stuart Phillips
Department of Kinesiology, Exercise Metabolism Research Group, McMaster University, Hamilton, ON, Canada
Brent C. Ruby
University of Montana, Montana Center for Work Physiology and Exercise Metabolism, Missoula MT, USA
Bengt Saltin
CMRC, University of Copenhagen, Denmark
Trent Stellingwerff
Nestlé Research Center, Lausanne, Switzerland
Mark Tarnopolsky
Departments of Pediatrics & Medicine, Neurometabolic & Neuromuscular Diseases, McMaster University Medical Centre, Hamilton Canada
Kevin Tipton
School of Sport and Exercise Sciences, University of Birmingham, United Kingdom
Phillip Watson BSc
School of Sport, Exercise and Health Sciences, Loughborough University, United Kingdom
The history of sports nutrition: from the early days to the future
Bengt Saltin and Asker Jeukendrup
The Greeks and the Romans
It could be argued that sports nutrition started in paradise when Eve gave the apple to Adam, to make him as strong as God. Nutrition has always intrigued humans. As far back as ancient Greece nutrition has been linked to performance and health. It was Hippocrates (460 BC - ca. 370 BC) who said “If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health”. The diet of most Greeks and Romans was predominantly vegetarian and consisted of cereals, fruit, vegetables and legumes, and wine diluted with water. When meat was eaten, the most common source was goat for Greeks and pork for Romans.
It is believed that the first documented information about a special diet of a Greek athlete was Charmis of Sparta. He is said to have trained on dried figs. There are other reports of figs being used as sports nutrition. Running was a big part of army training and there were professional runners who were used to send messages sometimes over long distances. The most well known runner was perhaps Pheidipphides, who has been linked to the origin of the marathon. Pheidipphides is said to have run from Athens to Sparta (240km) to ask the Spartans for help when Persians were about to destroy Athens. When the Spartans replied that they were just celebrating an annual ceremony and their laws did not permit them go to Athens to help, Pheidippides had to run back to convey the bad news.
“If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health”. |
Hippocrates (460 BC - ca. 370 BC) |
So he ran a total of 480km and he would have used figs as one of his main energy sources. It was estimated that with his 50 kg, he expended 28,000 kcal. (112,000 kJ). He also supposedly ran from Marathon to Athens (40km) which later became the marathon distance at modern Olympic Games). However, whether this run actually took place is still debated.
Olympic Games
According to Galen and other authors, at the end of the third century B.C., athletes believed that drinking herbal teas and eating mushrooms could increase their performance during competition in the ancient Olympic Games (Mottram 1988). There is also a report that states that a meat diet was introduced about the middle of the fifth century by Dromeus of Stymphalos, an ex-long-distance runner. Another account by Diogenes Laertius reports that Eurymenes of Samos consumed a meat diet recommended by his trainer, Pythagoras of Croton. However, by far the best accounts of athletic diet to survive from antiquity are those of Milo of Croton, a wrestler whose feats of strength became legendary and won the wrestling event at five successive Olympics from 532 to 516 B.C. His diet supposedly consisted of 9 kg (20 pounds) of meat, 9 kg (20 pounds) of bread and 8.5 L (18 pints) of wine a day. The validity of these reports from antiquity, however, must be suspect. Although Milo was clearly a large and powerful man, who possessed a prodigious appetite, basic estimations reveal that if he trained on such a volume of food, Milo would have consumed approximately 57,000 kcal (238,500 kJ) per day.
In South America, stimulants like mate tea, coffee and coca were used to increase performance. It has been reported that the Incas chewed coca leaves to cover the distance between Cuzco and Quito, in Ecuador (>1600km).
The first experimental approach
An experimental approach to the field of human muscle energy metabolism had its start in the middle of the 19th century. In 1842 John von Liebig stated that the primary fuel for muscular contraction was protein (Terjung and Horton 1988). However, within two decades this was proven wrong by von Pettenkofer and Voit (1866). Subsequent laboratory experiments focused on whether carbohydrates and fat could be used directly by contracting skeletal muscle. After some initial studies by Chaveux, supporting the view that fat had to be converted to carbohydrates before it could be used by muscle, Zuntz (see Carpenter 1931) claimed that both carbohydrates and fat were oxidized by skeletal muscle, not only at rest but also during exercise. This was confirmed in later studies by Krogh and Lindhard (1920). They also demonstrated that both fuels were used at the same time, in most instances, while protein normally did not play a role as a supplier of energy.
Initially protein was thought to be the only fuel but soon it was discovered that carbohydrate and fat could be used as fuel and that they were used simultaneously in most situations. |
An experimental approach to the field of human muscle energy metabolism had its start in the second part of the 19th century. Before 1900 it was generally thought that protein was the fuel for the muscle. In 1842 John Von Liebig stated that the primary fuel for muscular contraction was protein (see Terjung and Horton 1988). Laboratory experiments with humans were performed to unravel whether carbohydrates and fat could be used directly by contracting skeletal muscle. This laboratory approach gave clear cut answers demonstrating that lipids could be used by human skeletal muscle without first being converted to a sugar. It was found not only that both carbohydrate and fat could be used as a fuel, but in most conditions they are used at the same time. It was also concluded that protein did not play an important role as a fuel (see Terjung and Horton 1988).
At the same time other researchers had a more applied approach searching for the optimal diet for Arctic explorers crossing Ice Caps in the world. The Polar expeditions established that with an energy intake of up to 60-70 % coming from fat, subjects could still maintain a relatively high daily high exercise output. The sledge dogs could, however, perform their heavy task with a diet containing up to 90 % fat.
The importance of carbohydrate feeding
Important observations were also made by Levine and colleagues in the 1920s (Levine et al., 1924). They measured blood glucose concentrations in some of the participants of the 1923 Boston Marathon, which at that time was thought of as an almost impossible, unhealthy and grueling challenge, referred to in some papers as “violent exercise” (Larrabee, 1902). They observed that glucose concentrations markedly declined after the race in most runners. These investigators suggested that low blood glucose levels were a cause of fatigue. To test that hypothesis, they encouraged several participants of the same marathon the following year to consume carbohydrates during the race. This practice, in combination with a high-carbohydrate diet before the race, seemed to prevent hypoglycemia (low blood glucose) and significantly improved running performance (i.e., time to complete the race).
The importance of carbohydrate for improving exercise capacity was further demonstrated by Dill, Edwards, and Talbott (Dill et al., 1932). These investigators let their dogs, Joe and Sally, run without feeding them carbohydrates. The dogs became hypoglycemic and fatigued after 4 to 6 hours. When the test was repeated, with the only difference that the dogs were fed carbohydrates during exercise, the dogs ran for 17 to 23 hours.
Substrate utilization
Since these early days there has been continuous progress in our understanding of the importance of intensity, diet and training status for the substrate choice by skeletal muscle when exercising. Most of the knowledge we have today is derived from studies done in the 1930s. Our understanding of why carbohydrate usage is intensity dependent, why muscle training improves fat utilization and reduces lactate accumulation and why carbohydrate loading elongates time to exhaustion, is still limited.
Methodological improvements in the 1950-60s, such as the use of isotopes and the reintroduction of the biopsy needle (by Jonas Bergström) to take muscle biopsies, brought about new tools for more direct measurements of both substrates used and metabolites produced by muscles. In the 1960s the key role of fatty acids (FA) was recognized as was the storage and usage of muscle glycogen.
Studies in Scandinavia in the 1960s really improved our understanding of carbohydrate metabolism and have formed the basis of many popular sports nutrition recommendations. |
Since the sixties many exercise studies have investigated the relative importance of carbohydrates and fats for energy turnover, which factors limit the oxidation of these substrates and the regulatory mechanisms handling these substrates. There is consensus that fats play a larger role after training but to what extent serum and muscle triglycerides (TG) contribute is intensely debated. There is also debate about what the exact limitation is for the fat utilization during exercise, especially at higher exercise intensities. It has been suggested that the transport of FA into the muscle is the critical step but there is equally strong evidence of a key role for the mitochondrial respiratory capacity. The regulation of the FA uptake by the mitochondria also plays a role.
Although many questions are still unanswered, despite many years of intensive research, it is clear dietary carbohydrates are essential for optimal performance. Equally clear is that a high capacity for lipid oxidation in the active muscles of an endurance athlete is a requirement for optimal endurance performance. In part this is explained by limited glycogen storage capacity but there is probably a lot more to it than that. In the years to come we will learn more about the interactions between the diet and the training of an athlete.
Hydration
In the 80s there were a number of studies showing that dehydration could reduce performance and extreme dehydration could result in heat stroke and adverse health effects. These studies were soon followed up by work to optimize fluid delivery during exercise. Sports drinks appeared on the shelves of sports shops and supermarkets and were marketed toward a growing number of long distance runners and other athletes.
There was clearly a trend towards drinking more and more during endurance events as evidenced by the IAAF (International Athletics Federation) drinking guidelines and regulations for feed stations during marathon races. In 1953 the IAAF handbook for race organizers indicated that feed stations had to be provided only for marathon aces and only at 15 and 30 km. The 2009 guidelines indicate that water should be available at the start and finish of all events, for events up to 10km drinking should be provided every 2-3 km and for longer events refreshment stations have to be provided every 5km. In addition, water should be supplied midway between these refreshment stations. Effectively the total number of drinking opportunities during a marathon may be 17! Over the years the drinking messages got a bit clouded and many runners interpreted the guidelines as a directive to drink as much as possible. However, it is clear that drinking too much water can result in hyponatremia and more recently the drinking advice has stressed that overdrinking can be dangerous (see Chapter 5).
Micronutrients
Micronutrients have received some attention too. Since their discovery, vitamins have been more or less synonymous with good health because it was clear that a lack of these essential nutrients resulted in illness. Since the 40s and 50s it became common practice for sports people to supplement with vitamins in order to perform better. However, research consistently indicated that as long as there were no deficiencies, vitamin intakes over and above the daily recommended amounts did not enhance performance. Nevertheless, the use of vitamins and minerals, and antioxidants in particular, is still very popular. More recently, however, studies pointed out that large amounts of antioxidants could actually prevent (or at least reduce) normal training adaptations. It has also become clear that large doses of certain vitamins and minerals can have detrimental health effects.
The final note is a tribute to the early researchers in the field and to their accomplishments. Not only is reading their work enjoyable, we have also gained tremendous knowledge from their work. They contributed greatly to both to the applied aspects as well as our more fundamental understanding of possible limiting factors in endurance sports.
What is the optimal composition of an athlete’s diet?
Liz Broad and Greg Cox
The optimal composition
There is much debate about what athletes should eat and what the optimal composition of an athlete’s diet is. How much carbohydrate should it contain, how much fat and how much protein? Are vitamin and mineral requirements increased? The fact is that there is no one optimal diet for all athletes. The optimal composition of an athlete’s diet will depend on the sport the athlete engages in, the amount and type of training the athlete undertakes, and whether the athlete needs to manipulate their body weight or body composition. In brief, athletes need an individualized nutrition plan that is based on sound scientific principles and that is easily incorporated into their daily routine. This interface – the conversion of science into food – is where a skilled sports nutrition professional can apply their expertise. However, there are a few simple guidelines.
In any attempt to optimize and athlete’s nutrition, the first priority is making sure that the baseline nutrient requirements are met. |
Where to start?
The first priority is to consider baseline nutrient requirements. Fortunately these fall in line with recommendations for the general population in terms of most micronutrient (vitamins, minerals, fiber) needs and general trends in terms of the balance of macronutrients (carbohydrate, fat, protein and alcohol). This generally requires eating a variety of foods from all basic food groups, and creating a structure whereby food is distributed consistently throughout the day rather than at one or two time points. Once achieved, specific timing, quantities and food choices can be tailored to meet sport-specific requirements of the athlete.
One starting point could be to determine daily protein needs. Over the years, there has been a great deal of debate regarding the optimal protein intake of athletes. It is important to distinguish between requirements to maintain good health and the protein needs to optimize muscle growth and other adaptations to training.
Protein: the building blocks
The general recommendation for protein intake is in the range of 1.2-1.7 g•kg BM-1•d-1, regardless of type of exercise. (See Chapters 7, 9 and 11 in this book.) Dietary intake surveys of athletes frequently report that protein requirements are more than adequately met by the vast majority of athletes. However, some athletes have become overzealous with their focus on consuming protein, neglecting the importance of balance and fueling exercise or reducing carbohydrate intake in an attempt to reduce body fat levels. Given most athletes meet daily protein requirements because their energy intake increases to match training loads, the priority is to organize protein-containing meals and snacks around training sessions to optimize the adaptive response and assist recovery following exercise. For example, consuming a snack that provides 10-20g of protein immediately after resistance training for a rugby union player requires education and forward planning. Once their protein intake is planned to support training, the remainder can be distributed into the other meals and snacks to ensure a range of different food sources are used to meet essential nutrient requirements such as calcium (i.e. 3-4 servings of dairy), iron and zinc.
Given most athletes meet daily protein requirements, the priority is to organize protein-containing meals and snacks around training sessions to optimize the adaptive response and assist recovery following exercise. |
Carbohydrate: the preferred energy source
The other important macronutrient is carbohydrate, the predominant fuel source in moderate to high intensity exercise. It is now widely acknowledged that general recommendations for daily carbohydrate intake should be expressed as grams of carbohydrate per kilogram of the athlete’s body mass rather than a percentage of total dietary energy (Burke et al. 2001). Suggested carbohydrate intake guidelines for athletes based on daily exercise patterns and expressed relative to an athlete’s body weight have been recently developed (see Table 1). Interpretation of these guidelines into an athlete’s dietary plan should consider the athlete’s overall daily energy requirements, specific training volume and intensity, and requirements for growth and development (for children and adolescent athletes). Without an inherent knowledge of a sport, these guidelines can be easily misinterpreted. For example, it is not uncommon for a gymnast to train for 6-7 hours per day, over two training sessions. If you consider the training sessions duration alone, this would place their carbohydrate requirements at 10-12+g•kg-1 BM•d-1 according to current recommendations. In reality when the absolute amount of ‘activity’ is calculated within total training hours, the estimated amount of energy expended is quite small and has been estimated at 0.066 kcal•min-1•kg-1. The net result of true exercise energy expenditure in the sessions for an average 50 kg gymnast adds only 1200 kcal (5000 kJ) to their daily energy requirements. However, if the athlete consumed the amount based on training time alone of 10 g carbohydrate•kg BM-1•d-1 (equivalent to over 8000kJ), this would well exceed the energy expenditure of exercise, and thus highlights the need to ‘know your sport’. Although we have no definitive assessment of carbohydrate usage during gymnastics training, it is likely daily requirements are within 5-6 g•kg BM-1•d-1. As an alternate example, a 110 kg rugby union prop who trains twice a day in both strength and field sessions, incorporating high intensity bouts of exercise, would theoretically have carbohydrate requirements of 7-12 g•kg BM-1•d-1, or >770 g carbohydrate•day. Functionally, it is very difficult for these players to find the time and the capacity to eat that amount of carbohydrate. In reality, these players appear to train and recover well when carbohydrate intake is closer to 5-6 g•kg BM-1•d-1.
Carbohydrate intake guidelines for athletes based on daily exercise patterns and expressed relative to an athlete’s body weight have been developed. However, these guidelines have to be interpreted with caution and an inherent knowledge of a sport and its energy requirements is required. |
Carbohydrate when recovery times are short
When there is little time to recover (2-8h) it is important to make sure muscle fuel (glycogen) stores are restored as quickly as possible. To promote optimal glycogen recovery it is recommended to ingest 1 g of carbohydrate•kg BM as soon as practical following the session. This can be achieved by incorporating additional recovery snacks or, alternatively for athletes with a low energy budget, rescheduling the timing of the next meal (see Chapter 7). This can then be followed up with a similar amount in the subsequent 2h period if restoration of glycogen stores is the priority, as is the case following hard or prolonged workouts when training multiple times throughout the day. Consider whether you require carbohydrate during or before training, based on the goals of the training session itself and the relative importance of maintaining a strong work output throughout the entire session versus using the session to promote the metabolic and physiological adaptations to training. Once you have allocated appropriate carbohydrate to this, then as with protein, distribute the remainder of your requirements throughout the other meals and snacks for the day, using a range of different foods. In this instance, make sure this includes fruit and vegetables for their antioxidant content rather than making the carbohydrate predominantly cereal-based, and don’t leave it all to the last meal of the day. For those with very high energy needs, lower fiber options and liquid options (juice, cordial, flavored milks, etc.) are useful inclusions as otherwise the diet becomes too bulky.
Fat intake modified to meet remaining goals
Every athlete has an energy ‘budget’ which reflects their energy expenditure as well as body composition goals. Targets set for body fat/mass loss should be moderate (250-500 kcal or 1200-2000 kJ less than estimated daily energy expenditure), and similarly increased for muscle mass gain. The first priority is to meet daily protein and carbohydrate requirements to support training and facilitate recovery within this energy budget (see Chapter 20). This may mean reducing dietary fat intake (due to its high energy content) for athletes with a low energy budget (i.e. those trying to decrease body fat stores). Alternatively, there may be room to increase intakes of all 3 macronutrients to achieve energy demands. Most foods contain several different types of fats as evidenced on food labels. It’s important when choosing dietary fats, and fat-containing foods, that consideration be given to essential fat–soluble vitamins and essential fatty acids, as well as understanding the role of different dietary fats in lifestyle related disease and inflammatory processes. Good choices include consuming nutritious food sources of fats (such as avocadoes, oily fish, and nuts) and healthier sources of fats (olive oil, polyunsaturated oils, and canola oil).
The practicalities of developing a nutrition plan
For athletes who undertake routine daily training with little variation from one day to the next, it’s common practice among sports nutrition professionals to develop an individualized food and fluid intake plan based on an estimated average daily energy expenditure. For instance, divers typically undertake 2 hours of dry-land training in the morning, and 3 hours of afternoon diving practice. This daily routine is followed 5-6 days a week, with only minor adjustments in daily workloads. In this case differences in daily energy expenditure are minimal and are easily accommodated with a generic daily food and fluid plan that may only change in terms of food selection and variety.
An alternate approach is to develop a meal plan which can cater to athletes that have large daily fluctuations in training. For instance, a triathlete may undertake 6-8 hours of training including a mix of sustained aerobic activity and repeated bouts of high intensity efforts on high training days; and an easy 30-40 minute jog on their weekly rest day. In developing a meal plan for athletes with large daily fluctuations in energy expenditure, it’s important to ensure the daily meal plan can be easily manipulated by the athlete to compensate for changes in exercise patterns. Additional energy (namely in the form of carbohydrate) can be included before, during or after training to support daily exercise performance and recovery between exercise sessions. Of interest, Saris and colleagues (1989) found that male cyclists contesting the Tour de France modified their daily carbohydrate and energy intakes to reflect daily energy expenditure when supported by a professional team. Cyclists in this study consumed 94 grams of carbohydrate each hour while racing which accounted for almost half (49%) of their total daily energy intake. By comparison, Burke et al. (2003) found that male team and endurance athletes reported consuming only 3-5% of their total energy intake during training. The striking disparity between these two studies is likely to be a reflection of the organized support offered to elite cyclists by their professional team and the emphasis on maintaining ‘best’ performance from one day to the next throughout the course of the event. The take home message for athletes and coaches is to be organized and strategic when including additional foods and fluid to support the demands of training. This can only be achieved with forward planning and access to suitable foods and fluids.
An individualized food and fluid intake plan is usually based on an estimated average daily energy expenditure. |
Finally, athletes are faced with the added challenge of eating socially among family, friends, team mates and colleagues (for non-professional athletes). As clinical as sports nutrition guidelines may appear, athletes do not eat solely to support exercise performance and promote recovery between exercise sessions. Athletes must strike a balance to ensure they optimize their intake to support training and competition performances, while maintaining a flexible approach and attitude towards food to engage in social activities away from sport. Athletes and coaches are advised to seek advice from a sports nutrition professional who can help you achieve your goals.
Table 1: Guidelines for Carbohydrate (CHO) intakes in everyday training
The optimal pre-competition meal
Asker Jeukendrup
Even textbooks are sometimes confusing when it comes to pre-exercise meals. Some books will tell you to avoid carbohydrate (CHO) in the hour before exercise and some will tell you that you need it to improve performance. The last big meal is often planned 3-4 hours before a race but what should you eat and how much?
CHO loading in the days prior to exercise
The classic studies from Scandinavia in the late sixties that demonstrated the importance of muscle glycogen resulted in the development of a glycogen super compensation diet (see Chapter 1). Glycogen depletion in combination with a high carbohydrate intake resulted in a marked increase (super compensation) in muscle glycogen and enhanced subsequent endurance exercise performance. The proposed protocol to achieve these very high glycogen stores was pretty extreme and involved an exhausting exercise bout, no training at all for 6 days, a diet that consisted almost entirely of fat (3d), followed by a diet consisting almost entirely of carbohydrate (3d) (see Table 1). More recently, a less extreme diet-exercise regimen was almost equally effective in elevating pre-exercise muscle glycogen to these levels. With this moderate glycogen loading protocol it has also been shown that trained athletes can increase their muscle glycogen to very high levels in as little as one day by ingesting 10 g CHO•kg-1 body mass and remaining inactive. Muscle glycogen did not increase further during another 2 days of rest and high CHO intake. There is also evidence that well-trained athletes can maintain, or even increase, their muscle glycogen stores to very high levels in less than 24 h while training (67% VO2 peak) 2 h per day and consuming 10-12•5 g CHO•kg-1 body mass per day. It has even been suggested that trained athletes can greatly increase their muscle glycogen stores in <24 h by performing only 3 min of supramaximal exercise and then consuming a high CHO diet. This protocol potentially represents an improvement over previous regimens that have been extensively tested under laboratory and/or field conditions and further study is warranted.
Complicated strategies to glycogen load and ‘super compensate’ are not essential to achieve very high muscle glycogen concentrations prior to competition. |
Despite a greater reliance on muscle glycogen when pre-exercise levels are elevated, increased dietary CHO in the 1-7 days prior to exercise is generally associated with enhanced performance when exercise duration exceeds 90 minutes. This is most likely due to a delay in the point at which muscle glycogen availability is limiting for optimal exercise performance. The largest effects are observed during exercise trials to exhaustion (often referred to as endurance “capacity”) and are smaller in magnitude during tests of endurance “performance” that are not open-ended such as total work output in a given time or time taken to complete a certain distance or amount of work. During prolonged, strenuous exercise, rates of carbohydrate oxidation can be as high as 3-4 g•min-1, derived primarily from muscle glycogen.
CHO loading does not appear to further increase exercise performance when CHO availability is maintained high with a pre-exercise CHO meal and CHO ingestion during exercise.
Team sports and sprints
In shorter, more intense exercise bouts the benefits of glycogen loading are not apparent, probably because muscle glycogen availability is not a limiting factor in the non-CHO loaded trial in this type of exercise.
During single bouts of high intensity exercise, the effects of CHO loading are somewhat equivocal. Some studies have observed enhanced performance with elevated muscle glycogen levels following increased dietary CHO intake, while other investigators have observed no benefit of elevated pre-exercise muscle glycogen. In some of the studies the differences in performance were most obvious at the extremes of diet and may have been due as much to deleterious acid-base disturbances following consumption of a high fat-protein diet as to increased muscle glycogen availability following the high CHO diet.
With repeated bouts of high intensity exercise, increased muscle glycogen availability is associated with enhanced intermittent exercise performance (Balsom et al. 1999). Furthermore, increasing dietary CHO intake from 300 g•day--1 to 600 g•day-1 for two days prior to exercise improved long-term, intermittent exercise performance (Bangsbo et al. 1992), while ingestion of 10g CHO•kg-1 body mass improved intermittent running capacity during 22 h of recovery when compared with an isoenergetic diet without additional CHO (Nicholas et al. 1997).
It has been suggested that females may have a reduced ability to increase muscle glycogen levels during a period of dietary CHO loading but more recently it has been shown that with adequate energy and CHO intake, female athletes benefit from CHO loading as much as male athletes (see Chapter 15).
In conclusion CHO loading the days before competition is relevant for some but not all sports. The protocol employed to achieve this may depend on practicalities such a training and available time.
Carbohydrate 3-4 hours prior to exercise
Ingestion of a CHO-rich meal (containing 140 - 330 g CHO) 3-4 h prior to exercise has been shown increase muscle glycogen levels and enhance exercise performance. An increase in pre-exercise muscle glycogen is one explanation for the enhanced performance. Alternatively, because liver glycogen levels are substantially reduced after an overnight fast, ingestion of CHO may increase these reserves and contribute, together with any ongoing absorption of the ingested CHO, to the maintenance of blood glucose levels and improved performance during subsequent exercise (Casey et al. 2000).
Carbohydrate intake can suppress fat oxidation for several hours after ingestion. |
Despite plasma glucose and insulin levels returning to basal levels, ingestion of CHO in the hours prior to exercise often results in a transient fall in glucose with the onset of exercise, increased CHO oxidation and a blunting of fatty acid (FA) mobilization. These metabolic perturbations can persist for up to 6 h following CHO ingestion (Montain et al. 1991), but are not detrimental to exercise performance. Ann increased CHO availability apparently compensates for the greater CHO utilization. No differences in exercise performance have been observed following ingestion of meals that produced marked differences in plasma glucose and insulin levels (Wee et al. 1999). The effects of a high CHO meal 3-4 h prior to exercise on subsequent performance may be equivalent to those observed with CHO ingestion during exercise (Chryssanthopoulos et al. 1994), although this is not always the case (Wright et al. 1991) and there may be some important metabolic differences. The combination of a pre-exercise CHO meal and CHO ingestion during exercise may further enhance exercise performance (Wright et al. 1991). From a practical perspective, if access to CHO during exercise is limited or nonexistent, ingestion of 200-300 g CHO 3-4 h prior to exercise may be an effective strategy for enhancing CHO availability during the subsequent exercise period. Furthermore, ingestion of CHO may be effective in enhancing subsequent exercise performance when the recovery period is relatively short (4 h, (Fallowfield et al. 1995)).
If access to CHO during exercise is limited or nonexistent, ingestion of 200-300 g CHO 3-4 h prior to exercise may be an effective strategy for enhancing CHO availability during the subsequent exercise period. |
What to eat in the hour before a race?