Sports Nutrition Corner

Introduction

Carbohydrate

Fluid

Mail

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Introduction

We have all been told that we are what we eat, but how does nutrition affect athletic performance? Can the food we eat alter our endurance, strength, speed or even our mental performance? Do our carbohydrate, protein, fluid, vitamin, and mineral requirements differ according to our sport? When is the best time to eat and drink? Are you interested in learning about the latest information regarding ergogenic aids and supplements? What special nutrition concerns do athletic women have? Read on if you want to boost your athletic achievements through nutrition.

There are probably 3 basic dietary prescriptions for health and fitness. These apply to athlete and nonathlete alike. They are:

1. maintain a healthy body weight by adjusting food intake and exercise
2. eat less fat and specifically less saturated fats, such as those fats found in animal products and tropical oils
3. increase total carbohydrate, especially complex carbohydrate

In addition, we recommend eating less cholesterol, reducing intake of refined sugar, eating more fiber, fruits and vegetables and drinking alcohol in moderation. However, over and above these general recommendations, athletes have certain critical areas of nutrition. Given the extra caloric expenditure during exercise, requirements for most nutrients may be increased.

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Carbohydrate

The easiest and one the most proven ways of improving performance is by manipulating carbohydrate intake, particularly for endurance type athletes or those involved in sports like soccer, water polo, and basketball.

Carbohydrates are simple sugars or long chains of sugars which are linked together [starches]. Paradoxically, carbohydrates are the preferred fuel during exercise of high intensity but they are stored in extremely limited amounts in the body. This storage form of carbohydrate, called glycogen, is found primarily in muscles and liver. The glycogen in the muscle is used directly by the muscle which is being exercised. In other words, once its limited stores of glycogen are gone it cannot "borrow" from other resting muscles.
Depletion of glycogen by the working muscles leads to severely impaired exercise performance, which at its extreme is known as "hitting the wall". This makes obvious the need to 1) increase glycogen stores prior to exercise, and 2) supply carbohydrate during prolonged exercise.

How much carbohydrate is enough? We often express recommendations in terms of percentages of total calories. Even recreational athletes probably need to obtain 55-60% of their daily calories from carbohydrates. Most people can do this if they consume 3 grams of carbohydrate per pound of body weight. However, seriously training athletes probably require 4 grams of carbohydrate per pound body weight, or 60% of their calories from carbohydrate. For example, a 150 pound person who is cycling, say, 300 miles per week would require approximately 600 grams of carbohydrate daily. This carbohydrate would provide 2400 calories. Good examples of high carbohydrate foods are breads, cereals, grains, pasta, vegetables and fruits.

Each time you exercise muscle glycogen becomes depleted to some extent. By providing high carbohydrate intake every day, it more likely that you will restore the carbohydrate which has been used, thereby allowing for another hard bout of training the following day.

Although we typically think of endurance athletes as having high carbohydrate needs during exercise, other sports such as soccer have been shown to significantly drain stored glycogen. For example, studies have shown that muscle glycogen was depleted to less than a quarter of its preexercise levels after one soccer game. Most of this loss occurred during the first half of the game [Karisson]. Furthermore, supplying carbohydrate during events such as soccer games may help to spare muscle glycogen and increase performance, particularly during the second half.

Timing of Carbohydrate

This raises the question of timing of carbohydrate intake. If the carbohydrate is to be taken during exercise it should probably be in beverage form. Beverages may be more quickly absorbed than solids and present less potential for stomach upset. A sports-type drink that has a concentration of 6-8% carbohydrate is likely to be easily absorbed during exercise. Most people can tolerate 1/2 cup to 1 cup of liquid every 20 minutes. This tolerance depends upon the individual and the type of exercise performed. Jostling sports like running are associated with more complaints of gastric distress after drinking than are sports such as cycling.

To avoid hypoglycemia or low blood sugar during exercise, carbohydrate should probably not be consumed within 1 hour of the start of exercise. The best pre game strategy is to eat a light meal which contains 100 or so grams of carbohydrate 3-4 hours prior to exercise. Such a meal might look something like this:

	Food	Carbohydrate Grams	Calories
	Skim Milk, 1 cup	12	80
	1 Bagel, 4 ounces	60	320
	'Light' Cream cheese, 3/4 ounce	1	45
	Orange juice, 1/2 cup	15	60
	Water, 16 ounces	0	0
	TOTAL	88	505

In addition, one of the best times to provide carbohydrate to the body is immediately after a workout. Immediately after exercise the muscle is most avid to restore the glycogen it has used during exercise. Perhaps the best way to restore glycogen is to keep a drink which contains carbohydrate in your gym bag, and drink it prior to leaving the locker room or before you hit the shower at home. Alternatively, you can eat a high carbohydrate food, such as bread, bagels, pretzels, or fruit. The goal is to consume at least 50 grams shortly after exercise.

Carbo Loading

Athletes will sometimes eat a pasta dinners the night before competition and believe that they have "carbo loaded". As you will see in a moment carbo loading is far more difficult to acheive than simply eating one meal high in carbohydrates.

Occasionally it may be prudent to supersaturate the muscle cells with glycogen. This is done by "carbohydrate loading" and is of value if you plan to compete in an event which will last for at least 90 minutes and which will lead to exhaustion or near exhaustion. Carbo loading actually entails a weeks worth of preparation: beginning a week prior to the event exercise is cut by 50% every second day, thus sparing the depletion of glycogen. This will also allow for complete rest the day or two prior to competing. With four days to go the diet is increased to approximately 70% carbohydrate. For most people this would mean eating about 4 grams of carbohydrate per pound body weight.

According to this formula, a 150 pound person would therefore be required to eat 600 grams of carbohydrate per day during the loading period. This is a lot of carbohydrate!

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Fluid

Fluids are probably the most neglected aspect of the athlete's diet. It is not uncommon for recreational athletes to report that they consume on an average day an intake something like this: several cups of coffee, 2 colas and a few beers. That kind of fluid intake is not sufficient for several reasons, and physical performance will suffer as a result.

Heat is inevitably produced in the body during exercise. Our most effective way of removing heat is through sweating. For each 1 gram of sweat EVAPORATED from the skin, approximately 0.6 kcal of heat are removed. Fluid losses during exercise due to sweating can exceed 2 quarts or 4 pounds per hour. This is especially true in humid environments or in sports where padding is used since the sweat is not evaporated effectively. As dehydration progresses, performance becomes impaired. A loss of 2-3% in body weight due to sweating can reduce aerobic ability by more than 10%, while losses of 5% or more in body weight can result in heat stroke. Clearly, even relatively mild dehydration will significantly hamper competitive possibilities.

Type and Timing of Fluid Ingestion

How much liquid should be ingested? When?
The amount of fluid required is dependent upon how much sweat will be lost during exercise. Exercise in hot, humid environments will require more liquid intake to maintain performance. Two hours prior to exercise drink 2 cups of water, juice diluted by half with water, or a sports drink. To speed absorption the beverage should probably not contain more than 6-8% carbohydrate. Half an hour prior to exercise drink 1 cup of sports drink, or water. At this point fruit juice should probably be avoided since it contains fructose, a sugar known to increase complaints of stomach upset. During exercise most people can tolerate 1/2 to 3/4 cup of beverage each 20 minutes. Again, avoid fructose, and choose either water or a quickly absorbed sports drink, or a dilute carbohydrate-containing beverage.

To enhance rehydration, weigh yourself prior to and after your workout. By doing so you can determine how much fluid you have lost as sweat. For each pound you have lost during exercise, drink 2 cups of noncaffeinated, nonalcoholic liquid within a few hours of exercise to restore hydration. A 3 pound weight loss during the exercise session, for example, would necesitate drinking 6 cups of fluid.

As discussed above, the period immediatley post exercise is not only a good time to restore fluid losses, but is also an optimal time to restore carbohydrate. For that reason, a beverage which contains carbohydrate should be considered during the rehydration period. Alternatively, the athlete may want to eat a solid food containing carbohydrates while drinking plain water.

Types of Beverages

Recreational athletes are probably best served by drinking plain water. For example, someone who is walking a few miles each morning may not be at any significant risk of either dehydration or of carbohydrate depletion. However, for those who train at high intensities, or for prolonged periods of time, water may not be the best choice. The more serious athlete should be aware that the concentration of the beverage may significantly impact upon its rate of absorption and upon the liklihood of abdominal cramping, bloating or diarrhea when drunk during exercise.
The optimal carbohydrate beverage composition during exercise is probably one which provides a small amount of salt [sodium] and sugar [glucose, a glucose polymer or sucrose]. Beverages containing less than 6% carbohydrate are unlikely to extend performance, while those that contain greater than 8% are associated with intestinal upset. So look for a beverage which provides about 15-20 grams of carbohydrate, or 60-80 calories, per 8 ounces.

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Mail

You've read our sports nutrition material, but it just didn't cover what you had hoped; perhaps a specific nutrition question you've been wanting answered, or just something you're curious about. Maybe you've got a question about some of the material you've just read, or perhaps would just like to give us some feedback on it. Well, you can.
Send e-mail to nutricor@nismat.org with your questions and/or comments. We'll try to get back to you by e-mail, as well as by posting questions and answers here in the NISMAT Sports Nutrition Corner. As a courtesy to us, please read our disclaimer before posting any questions.

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