TABLE OF CONTENTS
EXECUTIVE SUMMARY 3
1.0 INTRODUCTION 4
2.0 BASIC NUTRITION 7
3.0 NUTRITION PRIOR TO EXERCISE 8
4.0 NUTRITION DURING EXERCISE 9
5.0 NUTRITION POST EXERCISE 10
6.0 COMPETITION NUTRITION 12
7.0 DIET "FADS" 14
8.0 CONCLUSION 18
9.0 REFERENCES 19
Endurance sports have become popular participation sports within the last few decades. Running, cycling, and triathlons are among the most notable endurance sports. An endurance sport requires physical activity for an extended period of time usually longer than an hour. The nutrition of endurance athletes is important and consists of three main food stuffs: carbohydrates, fats and protein. Carbohydrates are the most important to an endurance athlete whether it is prior to exercise, during or after exercise. During exercise glycogen stores are depleted and carbohydrates are the main source of fuel to replenish these stores whether it is during before or after exercise. Protein has the main role of synthesis and repair of muscle tissues after and during a workout.
Fats also play a role as a source for energy during low intensity exercise.
The many different diets that are currently available all claim that they work at reducing weight and that the diets are good for you. From the perspective of an endurance athlete none of these diets provide enough nutrition for the metabolic needs and amount of calories used except the Canada Food Guide. The Canada Food Guide does provide proper nutrition for an individual whether it is an endurance athlete or person looking to loose weight.
The nutrition of an endurance athlete is important and the best way is to follow a balanced diet and eat at regular intervals in conjunction with exercise. These healthy habits will lead to faster recovery times, increased injury prevention and increased performance.
Nutrition is an important aspect for all athletes and especially the endurance athlete because of the stresses placed on the body during activity. Nutrition is believed to improve performance up to 6% if used properly. Inversely the negative effects of nutrition can decrease performance up to 20% making proper nutrition important for the best performance in races and training.
There are many different diets and products out there for athletes to use but not all will give the optimal performance in endurance athletes. Some of these diets include "The Zone", Atkins and South Beach. There are also different times for different diets such as prior to exercise, during exercise and post exercise. There are significant differences required in a diet depending on when the energy for food is consumed. There are also different types of products available to fulfill the needs of athletes such as sport drinks, energy bars, energy gels, supplements.
There are different energy requirements for different people. For Example a 45kg female marathon runner will have a different energy requirement than a 125kg male football player. It is also shown that athletes have a higher energy requirement than your average person. Table 1.1 shows some daily energy intake values for different athletes during training.
TABLE 1.1 Reported Values for Energy Intake of Male Athletes during Training for Different Sports
Daily Energy Intake
MJ/d Kcal/d Reference
Triathlon 19.1 4584 Van Erp-Baart et al. (1989)
(ie Tour De France) 24.7 5928 Saris et al. (1989)
Track and Field 13.1 3141 Sugiura et al. (1999)
Rowing 14.6 3504 Van Erp-Baart et al. (1989)
There are three main sources for energy intake carbohydrates, fats and protein. Carbohydrates are used by the body in the form of glycogen and stored mainly within the muscles and liver. Carbohydrates can be consumed as simple sugars such as glucose or starches. Carbohydrate stores are the body's main source of fuel and the higher intensity the workout the more reliance on carbohydrate stores. The body will use more fat stores during low intensity training. Because of the limited amount of glycogen stores in the body these deposits can be depleted during a single workout and take up to 24-48 to replenish completely. It is important for endurance athletes to consume enough carbohydrates in meals to replenish the glycogen stores in the muscles and liver. Fat is another source of fuel and is mainly used at lower intensity workouts or training sessions. When training at 50% maximum oxygen intake (VO2max) about 2/3 of total energy requirement is from fat oxidation while one third is from carbohydrate oxidation. Protein is the third main source of energy and is only about 12-15% of total energy expenditure. Although this percentage will drop to about 5% energy requirement during exercise the absolute rate of protein degradation is increased during exercise. So an athlete will require more protein than an average person and different sports will require more protein than others such as a gymnast will require more protein than an endurance runner. The body uses all three energy sources during physical activity but carbohydrates are the easiest and most efficient to use by the body. Although the body uses all three for energy you could never completely cut one source of energy out of your diet.
These three main sources of energy can be looked at by a common measure and that is calories; One gram of carbohydrates is 4 kcal, one gram of protein is 4 kcal and, one gram of fat is 9 kcal. You can obtain the number of kcal in any food by multiplying the grams of protein by 4, carbohydrates by 4 and fats by 9 and summing the total of all three.
Fluid intake is an important part of any athlete's performance for excessive amounts of fluid loss through sweating can hinder performance. Inadequate amounts of fluid as well as too much fluid can affect other systems such as blood glucose levels, sodium levels and basic bodily functions. Vitamins and Minerals are also essential to life but not necessary to improving performance. If not consumed in adequate amounts they can hinder performance but essentially play very minor roles in performance provided they are consumed in sufficient amounts for bodily function.
These things are all important to nutrition of athletes and for exercise. It shows what types of molecules and compounds are required by the body to perform. This will help give us a better understanding when looking more specifically at athletes.
2.0 BASIC NUTRITION
The nutrition of an athlete prior to training needs to have enough nutrients for the athlete to perform at the appropriate levels and not "bonk" during the activity whether it be a race or workout. Also it is important that the right fuels go into the body at the correct times before a workout. As the saying goes "if junk goes in then junk will come out." This includes all nutrition throughout an athlete's day. When an athlete is exercising their body requires a certain amount of energy to maintain its regular functions, maintain body weight and have energy. It is important for athletes to maintain an ideal body weight and for training so that they perform at the highest level. Dietary information is always evolving and one of the best sources is the Canada Food Guide. The information contained teaches about balanced diets.
Table 2.1 Canada Food Guide Daily Serving Recomendations
Food Group Servings / Day
Fruits & Vegetables 5-10
Milk Products 2-4
Grain Products 5-12
Meat and Alternatives 2-3
The Canada Food Guide gives a range of servings that can be applied to different lifestyles. An active person will have more servings per day of all food groups than a non active person. The Canada Food Guide gives you a range of 1800-3200 kcals each day. Calories are a measure of energy and we can get this energy from carbohydrates. Based on Table 1.1 we can see that a triathlete requires more than the daily intake given by the Canada Food Guide.
3.0 NUTRITION PRIOR TO EXERCISE
The intake of the right food before exercise is important. It is important to be properly fueled for any physical activity. Many people can not work out right after a mean on a full stomach and that is because when you work out blood circulation is redirected away from the organs to the muscles performing the physical activity. This causes the food to sit in the stomach during the physical activity and to prevent it a pre exercise meal should be consumed 2 or more hours before. Carbohydrates are an essential part of every meal for an endurance athlete because they replenish glycogen stores for physical activity. Also hydration is important before any activity and leading up to any activity you will consume less fluids so there isn't that bloated feeling during exercise. Drinking Fluids is best at about 1 hour before exercise and then a little less at about 15-20min before exercise. It is also helpful to have a small amount of fast absorbing carbohydrate right before exercise to help prevent fatigue during an endurance activity. Essentially pre-exercise nutrition is similar to basic nutrition but this is modified when it is pre-competition nutrition as we will talk about later.
4.0 NUTRITION DURING EXERCISE
Nutrition during exercise is important to prevent fatigue and increase the endurance. An athlete that maintains good nutrition and fuel throughout physical activity can last for longer. Hydration is important because dehydration can impair performance.
Table 4.1 Physiological Effects of Sweat Loss
% body weight lost as Sweat Physiological Effect
2% Impaired performance
4% Capacity for muscular work declines
5% Heat exhaustion
10% Circulatory collapse and heat stroke
As you can see with Table 4.1 a small amount of sweat loss will impair performance while a little more can cause circulatory collapse and heat stroke. This is because sweat is composed of not only water but important electrolytes as well such as potassium and sodium. The replenishment of water and electrolytes can be achieved with a sports drink for fast absorption or with solid foods for slower absorption. It is important to be drinking about 600ml of fluid every hour during exercise to re-hydrate. Also ingesting some solid food such as a power bar is important for those endurance work outs. It is important to get about 20grams of carbohydrate every 30min during the workout. This can be accomplished with an energy bar, banana, fig bars or bagels. This prevents glycogen stores from depleting as fast and gives you energy lasting longer. You can also get carbohydrates from energy gels that contain mainly carbohydrates. The importance of nutrition during exercise is most important for those events that have a duration longer than one hour because short events you can get the nutrition before and after without any ill effects.
5.0 NUTRITION POST EXERCISE
Nutrition during the post exercise phase in important because an athlete wants recovery to be as quick as possible. The main focus of an athlete's nutritional recovery should be to replenish the glycogen stores and hydration. If these things are neglected in post exercise nutrition then it could result in muscle breakdown and the body is left feeling fatigued and exhausted during the next workout. During this recovery stage after a workout the body's immune system is weaker and anything to speed up recovery will help boost the immune system back to normal.
The best opportunity to replenish glycogen stores is the first hour after exercise because the rate limiting factor glycogen synthase in muscle glycogen synthesis is most active. The rate of glycogen synthesis is normally about 5% per hour but after rigorous exercise it rises to about 7% per hour. This is why products high in carbohydrates right after exercise is best such as energy drinks, fruit, and juice. It is important to not displace the carbohydrates with fats because then often the athlete will feel full and not completely replenish the glycogen stores.
The hydration after rigorous exercise is also extremely important to return fluid and salt balance to normal within the body. It is important to drink more fluids than needed because sometimes fluids are lost through the urine. A good estimate for hydration after workout is 2 cups of fluids for every pound of body weight lost.
Protein is another essential part of recovery although isn't completely understood as well as carbohydrates in the role of recovery. It is believed that protein aids in the synthesis and repair of muscle tissues and that without it the breakdown of muscle tissue would exceed muscle synthesis leading to loss of muscle mass. In endurance athletes it is believed that when protein is ingested during recovery it stimulates the muscle proteins of anaerobic energy production.
It is more important for athletes to replenish all nutrients especially if there will be more than one workout in a day. The marathon runner who does one workout a day will have more recovery time than the triathlete who does a swim in the morning then a bike in the afternoon.
6.0 COMPETITION NUTRITION
Nutrition during competition is slightly different than your regular routine. It involves changes both before and after the event. Leading up to the event you want to start building your glycogen stores by increasing the amount of carbohydrate intake about a week prior to the event. This will help insure that the endurance will not "bonk" during the event and lose all energy. Pasta, breads, fruits, vegetables and other items high in carbohydrates work great in accomplishing this. This is called carbo-loading and is common among endurance athletes. A pre-race meal is important to ensure the energy for the event and also that the meal has had time to digest. The general rule is about 2 hours before competition for the meal to be digested. Dairy and meats take longer to digest and should be avoided anytime less than two hours before competition. Hydration is also important leading up to competition and you should be keeping yourself overly hydrated leading up to the race so that the body can handle an excess of water before the competition.
Once the competition has begun then it is important to maintain hydration, electrolytes and glycogen stores so that the athlete can maintain their endurance for the entire event. This requires balancing intake of carbohydrates, electrolytes and fluid so there isn't too much hindering performance yet there is enough to maintain energy and function. This can be a complicated process and some people find gels tend to be absorbed quickly along with sports drinks for electrolytes and carbohydrates. Solid energy bars can sit in the stomach and do not absorb into the body as quickly but the carbohydrates are more concentrated than a gel or sports drink. You can follow the same rules as during exercise but sometimes people feel that is too much for a competition.
After the competition is complete then it is essential to replenish the glycogen stores. A post race meal is very important that is high in carbohydrates and protein. The carbohydrates will replenish glycogen stores and the protein will help with muscle regeneration and recovery. Competition nutrition may be slightly different than regular exercise but they are both built on the same premises just altered to give best performance.
7.0 DIET "FADS"
Nutritional diet "fads" have become commonplace in today's marketplace and it is up to the consumer to discern between the ones that will provide the most benefit and what will inevitably cause problems. Many diets will give small short term gains but can have negative long term effects such as heart disease.
7.1 THE "ZONE" DIET
There are numerous different diets and nutrition programs out there designed to increase performance and training but we are only going to focus on a few of them including the "Zone" diet as created by Dr. Barry Sears and published in his book The Zone. The Zone revolves around the idea that a regular diet has too many carbohydrates and that to better incorporate training and efficiency within the body they must be cut out of your diet. The Zone works in a 40-30-30 percent ratio of carbohydrates, fats and protein. With the belief that the more protein you have in your diet the more you are able to utilize fats which are higher energy molecules. When carbohydrates are consumed the blood-insulin level will rise and what insulin does is stores fat in the body. So the theory behind the Zone diet is that if you reduce the amount of carbohydrates then the insulin level will not rise as high and less energy will be stored as fats and instead the fats will be used for energy instead of the carbohydrates. You can do this by eliminating the unnecessary carbohydrates from your diet that have a high glycemic index such as processed wheat like rice. These will prevent the spike in your glycemic index and also force the body to use more fats for energy.
There are many reasons why this diet is not suitable for endurance athletes. This diet does not give the required amount of carbohydrates and energy required by endurance athletes to replenish glycogen stores after a few workouts in a couple of days. With three workouts in three days your glycogen stores will be depleted or very close to that and if you are not consuming enough carbohydrates to replenish these glycogen stores then you will not be able to perform at level required for even training an lead to infection and injury. There was a study that looked at different diets and performance and looked at athletes muscle glycogen content and bicycle ergonomic exercise until exhaustion. The athletes were on a high carbohydrate, high fat and normal diets and it showed that the athletes on a high carbohydrate diet could work till exhaustion three times as long as the athletes on the high fat diet (180 min for the high-carb as compared to 57 min for the high-fat). Another test had runners run 16km each day for three days and muscle biopsies were taken after the third run and it showed that the thigh muscle glycogen was almost depleted with diets of 40-60% carbohydrates.
This shows that the "Zone" diet is not very functional for endurance athletes. It may be more practical for regular people but for endurance athletes the practicality of this diet is not there and the scientific evidence does not support it.
7.2 ATKINS DIET
Dr. Robert Atkins first created his "low carb." diet book in 1970 and has since sold 15 million copies of it. The "Dr. Atkins New Diet Revolution" has become a diet used to help lose weight and it consists of limiting carbohydrate intake in your diet. From the perspective of an endurance athlete where carbohydrates are the main fuel source this diet would be detrimental to training and any physical activity. The Atkins diet begins with an "induction" period where participants are allowed to eat no more than 20 grams of carbohydrates per day. This amounts to 80 kcal of carbohydrates per day. After this "induction" period a participant can increase the amount of carbohydrates to no more than 40-90 grams of carbohydrates a day. This is a maximum of 360kcal per day from carbohydrates. This leads to a virtually unlimited amount of meats, poultry, fish and eggs that can lead to other health problems such as heart disease and cancer.
A participant in the Tour de France requires an intake of almost 6000 kcal per day and requires more carbohydrates. The intensity of the physical activity of a rider in the Tour de France will be very high so they will not be using fat stores and protein degradation will not be the primary source either. A rider will need to consume a food source of mainly carbohydrates to compensate for shrinking glycogen stores and increasing energy requirements.
The "low carb" Atkins diet is something that has become a fad diet for people who want to lose weight and not designed for endurance athletes because of the limited amount of energy from carbohydrates.
7.3 SOUTH BEACH DIET
The South Beach Diet as designed by Dr. Anthony Agatston for people to help lose weight. The goal of this diet is to help control cravings for "bad" carbohydrates by eliminating them completely from your diet and then slowly reintroducing them. It has three distinct phases that you complete during this diet where the third phase is ongoing. In the first phase you eliminate all carbohydrates. Your nutrition comes from meats, chicken, fish, eggs, nuts and vegetables. The idea is to eat 3 balanced meals a day and also eat enough to fill your hunger need. This phase lasts about 14 days and gives an expected weight loss of 8-13 pounds. In phase 2 you start re-introducing carbohydrates into your diet one product at a time. You also introduce foods that will not give you those hunger cravings between meals. You should still be avoiding starchy carbohydrate foods like potatoes, carrots, bananas and honey. During this phase a weight loss of about 1-2 pounds per week should be observed. Phase 3 begins once the individual finds a desired body weight. This is the maintenance phase and some more carbohydrates can be re-introduced but sparingly. It is essential that the individual maintains a degree of self control and does not consume those high glycemic index foods.
It is the initial weight loss period that some people have showed concern about because it could possibly be water-weight-loss because of the removal of carbohydrates. Carbohydrates help water storage in your body and when this is removed you will also lose the water that is retained with it. When your body doesn't have enough carbohydrates to consume then it also goes into a state of ketosis which is dangerous and causes weight loss.
These "fad" diets have all claimed weight loss and also have potential side effects. None of them include regular exercise as part of the diet and so the nutrition requirements of an endurance athlete are not looked after and none of these are suitable for any endurance athlete. The carbohydrate intake needed by an endurance athlete is not covered in the Zone, Atkins or South Beach diets.
Endurance athletes have a large caloric intake and their requirements are high above the general population. The Canada Food Guide gives a balanced diet to fill any persons' needs and an endurance athlete will have to multiply the amounts in the Canada Food guide to fit their caloric need. The various "fad" diets that are offered will not fill the caloric needs of an endurance athlete and also they all significantly reduce the number of carbohydrates in a person's diet which is the main energy source for an endurance athlete. It is also essential for an endurance athlete to have proper nutrition prior, during and post activity to prevent depletion of glycogen stores and "bonking". The nutrition needs of an endurance athlete are important and are essential to peak performance. It is also essential in injury prevention because it can aid in reducing the recovery times.
Gatorade Sports Science Institute. 2004. http://www.gssiweb.com/index.cfm
Gibala, Martin J. The role of protein in exercise recovery. Gatorade Sports Science Institue. 2004. http://www.active.com/story.cfm?story_id=11204&page=1
Harvard School of Public Health. Exercise. President and Fellows of Harvard College. 2004. http://www.hsph.harvard.edu/nutritionsource/Exercise.htm
Honig, Caryn. Nutrition and Supplements. Caryn's Corner. 2003. http://www.rice.edu/~jenky/caryns.corner.html
McArdle, Katch and Katch. Exercise Physiology: Energy, Nutrition and Human Performance. 3rd Edition. Lea Febiger Publishers. 1991. (ISBN 0-8121-1351-9)
Roberts, Amy. Nutrition for Triathlon. Asimba.com. 2000. http://www.sportsid.com/sid2000/health&fitness/triathlon2_asimba.asp
Sports Coach. Eating and Competing. 2004. http://www.brianmac.demon.co.uk/eatcom.htm
SportScience.org. 2004 http://www.sportsci.org/