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Sports Nutrition
For many athletes eating right can be challenging. This can be an even bigger challenge
for student athletes who live in dorms and residential housing on or near campus.
Frequently, very busy schedules prevent many athletes from preparing and eating wellbalanced nutritious meals. Sometimes nutritious foods are available in university
residential settings, but athletes who are not well educated about nutrition make poor
food choices and therefore, may suffer from marginal nutrient imbalances and
deficiencies that over time adversely affect their performance in athletics and in the
classroom.
Athletes need regular well-balanced, well-prepared nutritious meals and snacks to
maintain the high energy demands of training, competition and the rigor of an academic
program. Sickness, injury and general feelings of fatigue can be significantly improved
when an athlete takes a personal, active interest in his or her diet. The information
contained in this section addresses many topics related to general sports nutrition.
Athletes should be aware that a healthy, well-balanced diet can make an essential
contribution toward academic and athletic excellence!!
Some Basics
According to the American Dietetic Association and the American College of Sports
Medicine, there is currently no research indicating that athletes need a diet different from
the Dietary Guidelines for Americans, which advocates 55%-58% of energy intake from
carbohydrates, 12%-15% of energy intake from protein, and 25%-30% of energy from
fats (American Dietetic Association, 2000). Before exercise, a small meal or snack should
be eaten to provide enough fluid to maintain hydration, be low in fat and fiber to
facilitate gastric emptying and minimize gastrointestinal discomfort, and be high in
carbohydrates to maintain blood glucose levels (American Dietetic Association, 2000). It
is important to replace fluid and nutrient losses during exercise to avoid dehydration and
maintain blood glucose levels. The dietary goal of eating after exercise is to provide
enough energy and carbohydrates to replace muscle glycogen stores.
Click here for detailed information about nutrition and performance. (NCAA)
Here is a list of topical issues and questions that may be of interest to many athletes and
others who work with athletes.
Nutrition Health
Do the dietary habits of athletes affect their performance?
YES, one of the most important ways of improving athletic performance and maintaining
a healthy life style is achieved through following a balanced diet. What an athlete eats is
important for health, growth, body weight and composition, to prevent injury, and
ultimately to optimize performance (American Dietetic Association, 2000). Sound
nutrition is based on the wise selection of foods and beverages according to the stage of
the life cycle of the individual and the individual’s nutritional needs (Anderson and
McMurray, 1997).
What are some factors that prevent athletes from achieving a high level of nutritional
health?
Many factors prevent athletes from achieving a high level of nutritional health. According
to Burke (1995), an athlete may not be adequately nourished for the following reasons:
1. Poor understanding of sports nutrition principles.
2. Belief in misconceptions and myths.
3. Failure to recognize individual nutritional requirements related to a personal
training program, personal characteristics such as age, sex, and type of
physique.
4. Conflict between achieving good nutrition while trying to diet to lose body fat.
5. Lack of practical nutrition knowledge and skills.
6. Inadequate time and opportunities to obtain or consume appropriate foods due to
a busy schedule.
7. Poor money management that leads to inadequate food supplies.
8. Frequent travel, eating "on the road."
Dietary Needs
Why do athletes need a balanced diet?
According to the American Dietetic Association and the American College of Sports
Medicine, optimal nutrition enhances performance and recovery (2000). By eating a
variety of foods athletes can obtain all the nutrients they need to support the
development and growth of all body tissues, maintain healthy immune function, optimize
metabolism, and maintain healthy growth and weight control. For athletes meeting
energy requirements is the priority. Inadequate energy intake compromises performance
and health (American Dietetic Association, 2000).
Injury and tissue maintenance: Physical activity can lead to tissue damage. Time
needed to recover from injuries to muscles, tendons, and ligaments varies considerably
according to the extent of the damage sustained at the time of the injury. Adequate
dietary intakes will help provide the necessary building constituents that are needed for
tissues to fully recover. The process of rebuilding injured tissue is sometimes slow and
there are no miraculous nutrients yet known to science that cause instant recovery. The
secret is to eat a balanced diet over time to ensure the injured tissue receives a high
level of nutrients for optimal recovery via the bloodstream.
Immune function: According to Huffman-Goetz (1997), intense exercise and overtraining depresses the immune system, and moderate exercise enhances the immune
function. A diet rich in vital nutrients, especially anti-oxidants such as vitamins C & E
provides support for the immune system of athletes who are following a heavy training
program.
What are the United States dietary guidelines?
According to the Dietary Guidelines for Americans (4th ed., 1995 & 6th ed., 2005)
individuals should:
1. Eat a variety of foods.
2. Balance food intake with physical activity to maintain or improve weight.
3. Choose a diet rich in grains, vegetables, and fruits.
4. Select foods low in saturated fats and cholesterol.
5. Select foods with little or no trans fats.
6. Choose foods with moderate sugar content.
7. Choose foods that contain moderate salt and sodium content.
8. Drink alcohol in moderation, no more than 3-5 drinks per week. (Note: this
applies to those who are over 21 years of age and legally entitled to consume
alcoholic drinks).
What are the general nutritional needs of athletes?
Individual athletes differ in their nutritional requirements because of physical size,
gender, nature of the sport, climate, and time of the year/weather conditions, and body
weight and composition (American Dietetic Association, 2000). Therefore, it is difficult to
provide precise recommendations regarding the nutritional practices of individual athletes
in specific sports.
How do the energy requirements for athletes differ in individual and team
sports?
To maintain muscle mass, immune and reproductive functioning, adequate energy intake
is required. Energy balance is defined as a state when energy intake is equals energy
expenditure (American Dietetic Association, 2000). In general, an athlete's energy
requirements are met by keeping a balance between energy intake and energy
expenditure. The daily energy requirements of athletes will vary and depend on the body
size and activity level of the athlete (Murray and Horswill, 1997; American Dietetic
Association, 2000). Especially during periods of intense training it is essential to consume
adequate energy to maximize training effects (American Dietetic Association, 2000).
Team sports: Energy expenditures for team sports depend on the specific sport and the
position of the athlete. For example a midfielder in soccer might cover an average of 810 miles per game, while a defensive player covers less ground (Ekblom, 1986).
Additionally, energy needs differ between the sexes. For example, female soccer players
may not cover as much ground as a male soccer player, but the relative level of intensity
for female players is maintained at about 70% of oxygen uptake (VO2max), which is
comparable to the intensity level of males (Rosenbloom, 2006).
Short-duration, high intensity sports: Athletes who are involved in high intensity,
short duration sports (of less than 20 minutes) such as track runners, swimmers, sprint
cyclists, rowers, wrestlers, weight lifters and gymnasts essentially utilize glycogen as the
primary energy fuel (Sherman, 1992). Therefore it is essential that these athletes
consume adequate levels of carbohydrates to maintain stores of glycogen.
Long duration, moderate intensity sports: Marathon runners, cyclists, and cross
country skiers who need to sustain energy levels for longer periods of time need to be
able to burn fat for energy in addition to using glycogen. These athletes may use from
2,600-5,000 calories in competition. According to Murray and Horswill (1997): a runner
who completes a 10 mile run at a 6 min / mile pace in the morning and 8 miles at 5 min
30 secs / mile in the afternoon would require an intake of at least 3000 calories in
addition to his or her basic energy needs to maintain adequate glycogen stores and
energy requirements.
Are there special energy considerations for female athletes?
While it is important for all athletes to consume adequate amounts energy, it is even
more important for female athletes. Studies suggest that female athletes consume less
total energy (calories) than male athletes (Burke, et al., 2001; Loucks, 2004). This may
be due in part to female athletes striving for low body weight and lower percentage of
body fat. Energy intake is a special concern for female athletes because if energy intake
is too low to support the demands of training and competition reproductive disorders can
result from hormonal imbalances (Loucks, 2004). Inadequate energy and macronutrient
intake can also lead to changes in growth, decreased bone mineralization and decreased
performance.
Liquid Intake
How much liquid does an athlete need?
Fluid intake is critical to ensure that an athlete can perform up to his/her trained or
conditioned ability (American Dietetic Association, 2000). Thirst is not a good indicator of
body water requirements. In general by the time you are thirsty, your body already has
about a 2% body weight lose (Sawka & Montain, 2000). Since heat production is
increased with ALL forms of exercise, it is essential for athletes to maintain fluid balance
so the excess heat can be dissipated through the production of sweat. With the
evaporation of sweat, heat is lost from the blood that circulates near the skin, cooling the
body. The rate of sweat loss varies between people and with the ambient temperature
and humidity. As the heat increases so does sweat production to keep the body cool. In
general, the higher the heat, humidity, and intensity of the work, the greater the
requirements for hydration are.
GENERAL GUIDELINES:

Consume enough fluids to avoid thirst.

Limit consumption of caffeine and alcohol
containing fluids. They act as diuretics and
can increase fluid loss.

Drink at least 14 to 22 oz of fluid 2 hours
before exercise.

Drink at least 4 to 8 oz of fluid immediately
before exercise.

Drink at least 6 to 12 oz of fluid every 15 to
20 minutes during exercise (whether thirsty
or not).

Drink at least 16 to 24 oz of fluid after
exercise for each pound of body weight lost
during exercise.

Drink at least 8 oz of fluid with each meal.


Drink at least 8 oz of fluid between meals
To assure adequate hydration prior to
training and competition athletes should
consider ingesting an additional 250 -500
ml of fluid 30 minutes before exercise.
Note: Sports drinks (such as Gatorade®) which contain electrolytes and ~ a 6%
carbohydrate solution should be used in place of water, regardless of the length or
intensity of the activity. Sport drinks improve the delivery of both carbohydrate
and water to the muscles. Sport drinks can help maintain blood glucose levels and
decrease the risk of dehydration (Position of the American Dietetic Association,
2000). More importantly, they help to maintain blood volume and the delivery of
fuel to the brain. Mental fatigue leads to muscle fatigue, so keeping the brain wellfueled is critical to athletic performance.
Are you hydrated?
Water makes up to 70% of total body weight. An average 75kg human contains about
60% or 45 liters of water (Sawka and Pandolf, 1990). Athletes with lean body and low fat
mass have higher water content. The fluid losses of athletes depend upon the intensity at
which the athlete is exercising, an individual genetic predisposition for sweating, his or
her level of fitness, the environmental and climatic conditions, and the amount and type
of clothing and headgear worn by the athlete (American Dietetic Association, 2000;
American College of Sports Medicine, 1996; Sawaka and Wenger, 1988). During low
intensity exercise in cool and dry settings sweat loss can be less than 500 ml/h. In hot
and humid conditions during intense exercise sweat loss may exceed 3 liters/hour
(Sawka and Pandolf, 1990). Therefore, fluid intake should be carefully monitored to
ensure that fluid needs during these conditions are met by adequate intake. With normal
kidney function your hydration level is indicated by the color of your urine. When the
urine is darkly colored, and the urine volume is low the athlete is in a dehydrated
physical state and should consume more fluid until the urine returns to a normal, clear or
very light amber color. Please note, certain medicines and vitamins may cause the color
of the urine to change unrelated to hydration. If any of these have been taken, this test
is unreliable. A simple test can help protect your health.
Using the Hydration Chart
Match your urine color to the closest color in the chart and read the hydration level.
Urine color ratings of 1, 2 and 3 are considered to be well-hydrated(Armstrong, 2000).
However, color ratings below 3 suggest some dehydration and therefore loss of physical
and mental performance. Based on these results you can make changes to the volume
and timing ofyourfluid intake. This chart should only be used as a guide.
Hydration Chart
1
Optimal
2
3 Well Hydrated
4
5
Dehydrated:
You need to drink
more water
6
7
8
Seek Medical
Aid:
May indicate
blood in urine or
kidney disease
Water consumption Table
The amount of fluid required to maintain adequate hydration varies depending not only
on the type of activity, but the temperature. The chart below provides guidelines of how
much replacement fluid should be taken each hour. Note, hourly fluid intake should not
exceed 1.5 quarts and daily fluid intake should not exceed 12 quarts.
Heat
Categor
°F
Water Consumption Table
Easy Work
Moderate
Work
Hard Work
y
1
2
Water
Water
Water
Intake
Intake
Intake
(Quart/Hour
)
(Quart/Hour
)
(Quart/Hour
)
½
¾
¾
½
¾
1
¾
¾
1
¾
¾
1
78°81.9
°
82°84.9
°
3
4
85°87.9
°
88°89.9
°
5
>90°
At heat category 5,
1
Easy work –
1
Moderate
1
Hard work –
rest. Sit or stand in the
shade if possible.
walking on a
hard surface
work –
walking in
walking in
the sand at
at less than
2 mph
the sand at
2.5 mph
2.5 mph
with a load
with no load,
calisthenics
The fluid replacement volumes will sustain performance and hydration for at least 4 HOURS
of work in the specified heat category. Fluid needs can vary based on individual differences
and exposure to full sun or full shade.
Adapted from: U.S. Army Center for Health Promotion and Preventive Medicine Health
Information Operations Division (June 2004) Retrieved from http://chppmwww.apgea.army.mil/heat July 2008.
Special Environmental Conditions
The risk for dehydration increases significantly in hot and humid climates (American
Dietetic Association, 2000; American College of Sports Medicine, 1996). When the
relative humidity is high, the body cannot dissipate heat by evaporating sweat, instead
the sweat just drips off the body. When the temperature and humidity are both high
there is an increased risk of heat illness. In these conditions sports competitions should
be postponed, rescheduled or canceled (American College of Sports Medicine, 1996). If
this is not possible, every precaution should be taken to assure that the athletes are well
hydrated and are monitored for heat illness.
While the risk of dehydration is greatest in hot climates increase, dehydration can occur
in cold climates (American Dietetic Association, 2000; Adner, 1988). In cold climates it is
common for dehydration to occur due to inadequate fluid intake, respiratory fluid losses,
and sweating from wearing insulating clothes during exercise.
High altitudes, above 2,500 feet, can increase fluid replacement requirements. In high
altitudes, fluid is lost due to mandatory dieresis, respiratory losses, and decreased
appetite (American Dietetic Association, 2000). Respiratory water losses may be as high
as 1,900 mL in men (Butterfield, 1996) and 850 mL in women (Butterfield, 1992). To
maintain adequate hydration and proper kidney function, fluid intake should be increased
to as much as 3 to 4 L per day (American Dietetic Association, 2000).
What are the effects of dehydration on athletic performance?
Under normal conditions the water content of the body is constant. An imbalance
between fluid intake and fluid losses results in dehydration (Barr, 1999; Brouns, 1993).
The volume of fluid varies widely among athletes but in general the amount of fluid
needed to compensate for the fluid lost is about 50% of the sweat loss (Noakes et. al.,
1988).
Dehydration occurs when fluid losses are greater than 1% of body weight, and athletic
ability is measurably impaired with a 2% loss of body weight. This means a 100 lb
athlete who loses 2 pounds during
exercise may no longer be performing up
to his/her trained ability because of the
excessive body fluid loss.
Even slight dehydration can have
noticeable and negative effects on
performance during high intensity
exercise. Dehydration causes fluid
imbalances in the body that can lead to
impaired mental focus, impaired energy
metabolism, and important changes in
electrolyte concentration levels. Plasma
fluid volume plays an important role in
maintaining a normal blood flow through
the tissues.
Dehydration causes a decrease in plasma
volume, and as a result leads to decreased blood flow. This will lead to reduced transport
of substrates and oxygen to the muscles needed for energy production. This will result in
decreased energy and a marked, rapid onset of fatigue (Brouns, 1993). Typical
symptoms of inadequate fluid intake during exercise include: thirst, fatigue, loss of
coordination, mental confusion, irritability, dry skin, elevated body temperature, and
reduced urine output. Dehydration can lead to heat illness and an increased risk of
kidney stones.
Athletes should stay well hydrated before and during exercise, and make sure that cool
fluid is available at all times, because cool fluid leaves the stomach more quickly. Drinks
can be flavored and sweetened sufficiently to encourage athletes to drink. One teaspoon
of salt per liter helps to ensure complete hydration and normalize the body's sodium
levels. Some commercially available sports beverages are available and can be used to
sustain normal electrolyte levels (ACSM, 1996; Broad, 1996; Burke, 1995).
Team sports: Athletes who are involved in team sports such as soccer have tended in
the past to limit fluid intake to the half-time break. This is not adequate for maintaining
optimal fluid levels in the body. Athletes should drink fluids freely on an as needed basis.
Coaches and team trainers should encourage athletes to drink at all times, and attention
should be given to athletes with above average sweat rates to make sure they are
drinking appropriately (Broad, 1996; Burke, 1995).
Short duration and high intensity sports: Athletes involved in high intensity sports
can experience rapid and significant dehydration. Depending on the level of competition,
efforts of less than 30 seconds do not involve significant dehydration (Horswill, 1991).
However, participation involving extreme efforts of greater than 30 seconds in duration
can cause rapid weight loss from fluid depletion (Horswill, 1994).
Long duration moderate intensity sports: Athletes who compete in long distance
running, cycling, and skiing events that last longer than 30 minutes generally have
access to fluids at regular intervals. Sometimes runners restrict fluid intake when
experiencing gastrointestinal problems that are already due to dehydration, and increase
the effects of dehydration. Athletes need to practice in training drinking habits that will
be effective in maintaining adequate body fluid levels during competition.
Carbohydrate Intake
What are the carbohydrate (CHO) requirements of athletes?
Carbohydrates are classified as either "simple" or "complex".
Some common simple carbohydrates include glucose, fructose,
and sucrose, and are typically associated with sweet foods and
ripe fruits. The complex carbohydrates are either digestible
(starches) or indigestible (fiber). The digestible complex
carbohydrates are ultimately "digested" to the simple
carbohydrate glucose when they are consumed. While the
ultimate "fuel" for muscles is glucose, complex carbohydrates
usually carry with them other nutrients, such as B vitamins,
which are necessary for muscles to get energy from the foods we’ve eaten.
Carbohydrate (CHO) in the form of glycogen is the body's main fuel for high intensity
activity (American Dietetic Association, 2000). Glycogen is the storage form of glucose
and it is needed for both endurance and strength events. CHO is stored as long chains of
glucose units in the liver and in the muscles in the form of glycogen. The glycogen
content of the liver is about 100 grams. This quantity can change depending on the
amount of glycogen broken down from the supply of blood glucose and the amount of
glucose supplied to the liver after food intake. Muscle and liver glycogen levels are
relatively small, because the body has a limited capacity to store it, and are reduced
during training and competition (Brouns, 1993; Murray and Horswill, 1997).
General recommendations for carbohydrate consumption for athletes range from 6 to 10
g/kg body weight (American Dietetic Association, 2000). However, this amount varies
depending on total energy expenditure, type of sport, sex of the athlete, and
environmental conditions.
What are the effects of carbohydrate on athletic performance?
Dietary carbohydrates increase the amount of CHO available to the working muscles.
When the levels of CHO are reduced exercise intensity and length of activity decrease,
and fatigue rapidly increases. Costill (1988) recommended that athletes ingest 9-10
grams CHO/kg of body weight per day to restore and maintain muscle glycogen levels.
Athletes should consume a diet in which at least 60% of the total energy is supplied by
carbohydrate and no more than 10% of these calories in the form of simple
carbohydrates (Costill, 1993). Good sources of carbohydrates include pasta, bread,
cereal, legumes (beans), fruits, and vegetables. Pre-exercise carbohydrate loading has
been shown to improve performance (Sherman, 1995). Providing a constant supply of
carbohydrates is the best, simplest, and safest means of "carbohydrate or glycogen
loading". Because glycogen is only efficiently stored when an athlete is well hydrated, it
is also important to make certain that plenty of fluids are consumed while eating
carbohydrates.
Glycogen stores are especially important for athletes involved in team sports. Maximizing
muscle glycogen stores provides greater energy reserves for performance resulting in
greater endurance and delayed fatigue (American Dietetic Association, 2000).
Athletes involved in short duration high intensity sports also require high carbohydrate
intakes. Athletes in sports such as wrestling, sprinting and similar sports should ingest
high carbohydrate diets during intense periods of training. A high carbohydrate diet
allows higher training intensities (Nevill et. al., 1993).
Athletes who train for long hours and compete in endurance sports should consume 65%
to 70% of their energy from carbohydrate (American College of Sports Medicine, 1991).
Before long duration activities athletes should include at least 3 days of intake which
includes 800g carbohydrate per day (or 6-10 g CHO/kg/body weight/day) and a week of
tapered workouts that ends in complete rest the day before the competition. This
carbohydrate loading plan maintains high glycogen stores in the body (Food and Nutrition
Board, 1989). In addition, ingesting glucose during prolonged activity can increase
carbohydrate oxidation, resulting in increased performance (Baile, et al. 2000).
Are there gender differences for carbohydrate requirements?
There may not be as big a difference as was once thought. New research has shed light
on how women store and utilize carbohydrates. When the smaller body size of the female
athlete is taken into account and the relative and absolute intakes of carbohydrates for
females were matched to males, the gender differences in glycogen storage disappeared
(Tarnopolsky et al., 2006; Rosenbloom, 2006). In another study, it was shown that men
and women utilized carbohydrates at similar levels when fed glucose during prolonged
exercise (Baile, Zacher, & Mittleman, 2000). So, as long as female athletes consume an
adequate percentage of total energy intake from carbohydrates, the storage and
utilization of glycogen should be similar to that of male athletes.
A concern for female athletes is the effect of the menstrual cycle on performance. It has
been observed that the performance of female athletes is affected by the phase of the
menstrual cycle she is in (Campbell, Angus, & Febbriao, 2001). However, when females
consumed glucose during exercise, the difference in performance due to menstrual phase
disappeared. So carbohydrate consumption is especially important for female athletes.
How can an athlete ensure optimal levels of carbohydrate (CHO) before an athletic
event?
Pre-exercise / competition CHO intake: The importance of dietary intake of CHO for
athletes before exercise or competition has not been well established (American Dietetic
Association, 2000). The majority of energy released during muscle work is derived from
CHO and fat (Brouns, 1993). Depending on the level of intensity of the exercise one of
the fuels may become the major energy deliverer. During the resting period most of the
energy is derived from fat. The possible energy supply ratio is in the order of 90% fat to
10% CHO. During more intense sport activity glucose is mobilized from the liver and the
muscle glycogen pool to deliver energy. Fatty acid mobilization increases until a steady
metabolic state has been achieved (Newsholme and Start, 1973). At higher exercise
intensities CHO is the most important fuel source (Brouns, 1993).
When CHO stores in muscle and liver are increased athletes are able to perform longer
and at higher intensity levels. The amount of glycogen available in the muscle is an
important factor in performance. As soon as the muscle glycogen stores have been
depleted the ability to perform repeated high intensity, contractions will be reduced
(Maughan and Greenhaff, 1991). Depletion of glycogen stores results in fatigue and
decreased performance.
Exercise intensity and duration: Endurance athletes, such as distance runners,
cyclists, and swimmers, who train at a high level of energy output on a daily basis,
require 65% to 75% of total calories from carbohydrates or 4.5 -6.0 g
carbohydrate/kg/body wt/day to optimize performance. High carbohydrate diets can also
increase time to exhaustion with short-term intense exercises (Wilkinson and Liebman,
1997). Glycogen depletion should be prevented by a high CHO diet during training and
periodic rests to allow the muscle to rebuild glycogen stores (Superko, 1989). Tiredness
associated with over training can be caused by lowered glycogen stores (Hubinger et. al.,
1995). Foods rich in complex carbohydrates and a great variety of grains, legumes, fruits
and vegetables will allow sufficient glucose absorption and maintenance of glycogen
stores (Wilkinson and Liebman, 1997). Additionally, drinking a sport drink with
carbohydrates during exercise can help stave off fatigue by maintaining blood glucose
levels and improve performance (American Dietetic Association, 2000). During periods of
sustained exercise, athletes should consume 0.7 g carbohydrate/kg body weight to
extend endurance performance American Dietetic Association, 2000; Coggan, 1991).
Type of CHO intake: CHO intake should be light (approximately 300 Kcal), and
obtained from CHO foods that the athlete has tried during the training period and found
to be easily digested. CHO should have a low fiber content and taken with a moderate
amount of protein to maintain good blood sugar levels and plenty of fluids. Pre-exercise
CHO supplementation should contain 1-5 g CHO/kg body weight. Liquid carbohydrate
intakes at the lower end of this range are better tolerated than solid meals and higher
intakes when consumed close to competition.
Carbohydrate loading: Depletion of muscle glycogen can cause a decrease in exercise
energy output. The use of CHO loading to maximize muscle glycogen stores at the
beginning of exercise or competition could be beneficial for athletes who participate in
continuous exercise for more than 90-120 minutes (Wilkinson and Liebman, 1997). The
classic method of CHO loading recommended by Bergstrom et. al., (1967), includes
glycogen depletion from a long low intensity workout, followed by loading. The athlete
should eat a CHO rich diet (pasta, potatoes, bread other grains or starchy vegetables) in
which 90% of the total k/cal are from CHO, for 2-3 days to allow the muscles to become
saturated. This involves CHO intakes of 500 to 600 g per meal. The classic method of
loading occurs when the athlete depletes the muscle reserves of glycogen by engaging in
a strenuous workout (endurance runners, a 2-3 hour steady run) and then eats a very
restricted, low CHO diet for 3 days, followed by a CHO loading phase of 2-3 days in which
a very high CHO diet, in which more than 90% of total k/cal are consumed from CHO.
For many athletes a low CHO diet for 3 days may cause hypoglycemia, irritability, and
extreme chronic fatigue. A modified version involves "tapering down" of exercise during
the 6 day prior to the event. Daily CHO intake is slowly increased from an initial level of
approximately 350 to 550g or 70% of total k/calories during the last 72 hours preceding
competition (Hoffman et. al., 1991). This method will increase muscle glycogen stores
20-40% above normal (Coyle, 1995). Although CHO loading can increase high intensity
exercise time and duration it will not be effective until at least after the first hour of
exercise has been completed for example, at 8-10 miles in the marathon (Coleman,
1991). CHO loading may initially create a feeling of heaviness or stiffness in the muscles
that have been depleted of glycogen before an event and in some individuals may
contribute to muscle cramping and
premature fatigue (McArdle et. al., 1991).
Timing of CHO intake: Pre
exercise/competition: Ingestion of a CHO
snack or beverage 15 minutes to 1 hour
before exercise can lead to hypoglycemia
during exercise (Costill et. al., 1977;
Koivisto et. al., 1981). Consumption of a
glycogen replacement drink during long periods of exercise has been found to improve
work performance. In general, a pre-exercise/competition meal should be consumed at
least 2-3 hours before the session to allow adequate time for complete gastric emptying
and minimize
gastrointestinal discomfort (Wilkinson and Liebman, 1997).
CHO intake during exercise: According to Coggan et. al., (1991) CHO intake during
exercise should be sufficient to provide a minimum of 45-60 g of total CHO to sustain
high performance energy levels. Blood glucose concentrations are maintained during
moderate / intense exercise by supplying glucose at a rate of 45g/hour (Coggan et. al.,
1987: Murray et. al., 1989). CHO supplementation during prolonged endurance exercise
or at least 30 minutes before the onset of fatigue are effective in delaying fatigue (Coyle,
1992).
Post exercise CHO intake: The timing and composition of the post exercise meal will
depend on whether muscle glycogen stores were depleted (American Dietetic
Association, 2000). The type of CHO taken after exercise can influence the rate of muscle
glycogen re-synthesis and muscle recovery. This effect is mediated by glycemic and
insulinemic responses to different CHOs (American Dietetic Association, 2000; Febbraio
et. al., 1994; Burke, 1993). Fructose intake is associated with lower blood glucose and
insulin levels compared to sucrose (American Dietetic Association, 2000; Febbraio et. al.,
1994). In order to maximize the rate of muscle glycogen synthesis it is recommended
that athletes check the glycemic index (GI) of different CHO foods (Wilkinson and
Liebman, 1997). CHO diets with a high GI that are eaten within a 24 hour period after
prolonged exercise allow for greater glycogen synthesis compared to the CHOs with low
GI (Burke et. al., 1988). The rate of glycogen re-synthesis is more rapid in the first 2
hours following exercise. Increasing CHO consumption from 188g to 648 g/day will result
in greater muscle glycogen re-synthesis during the 24 hour post-exercise period (Costill
et. al., 1981). According to Wilkinson and Liebman (1997), eating fructose post exercise
compared to glucose induces more liver glycogen synthesis but less muscle glycogen
synthesis. High CHO foods and beverages such as fruits or beverages or commercially
available CHO drinks with a high GI are good choices for promoting post-exercise
glycogen re-synthesis (Wilkinson and Liebman, 1997).
Fat Intake
What are the fat requirements of athletes?
In most normal circumstances fat provides a secondary source of energy for athletes.
The importance of fat as a source of energy depends on the duration and intensity of the
activity added to the availability of CHO (Brouns, 1993). Fat is stored in the body in fat
cells as triglycerides. Most of the fat cells are found under the skin, and around the
internal organs (Brouns, 1993). The optimal level of body fat depends on the sex and
age of the athlete as well as heredity (American Dietetic Association, 2000). Body fat
values (indexes) for athletes range from 5% to 12% in men and 10% to 20% in women
and vary between sports and positions in the specific sports (Position of the American
Dietetic Association, 1989). Athletes should strive to have a fat intake that does not
exceed 25% of total calories (Position of the American Dietetic Association, 2000). There
is no evidence to support consuming a diet with less than 15% of calories from fat. Diets
that are higher carbohydrates and lower in fat are important for optimizing athletic
performance. Eat a reasonably low fat diet with plenty of carbohydrates to fuel activity.
Are there gender differences in fat intake requirements?
Fat consumption is often limited in female athletes wishing to lower body weight.
However, fat plays an essential role in maintaining menstrual function. Fat intake for
female athletes should be 20-25% of total energy consumption.
What are the effects of fat intake on athletic performance?
Fat is an energy source that provides essential fatty acids and carries fat soluble vitamins
(vitamins A, D, E, and K). In highly trained athletes the total fat stored in the adipose
tissue is 5% to 15% in males and 10% to 25% in females (Brouns, 1993). Total fat
intake is likely to be higher in athletes (such as linemen football players) who consume
high levels of energy (more than 4000 kcal) in order to maintain muscle mass than
among the general population (Wolinsky, 1997).
Team sports: A football player who weighs 100 kg (220lb) and 10% body fat has about
66,000 k/cal of stored fat energy to fuel him for days of moderate to intense training.
Since fat is transported and oxidized slowly by active muscle its contribution to energy
production during exercise is limited (Murray and Horswill, 1997).
According to Murray and Horswill (1997), during short duration high intensity sports,
fatty acid oxidation provides energy for cellular functions and muscle contraction.
Athletes can benefit from fat oxidation during low intensity phases of interval training.
Long duration moderate intensity sports: Fat metabolism as an energy source
increases as exercise intensity decreases. During ultra-endurance exercise, such as
distance runners and cyclists, fat metabolism becomes the principal source of energy
(Murray and Horswill, 1997).
Protein Intake
What are the protein requirements of athletes?
Protein is one of the most essential nutrients in our body. It has a wide range of
physiological functions that are required for achieving optimal physical performance.
Protein forms the structural basis of muscle tissue, is a major source of energy for
muscle contraction, and is also the major component of enzymes and blood in the
muscle, and makes up about 45% of the human body.
The requirement for protein is dependent on total energy intake, the amount of training
an athlete does, and the intensity of that training. Of these factors, the most important
one is total energy (calorie) intake. Increasing energy intake from carbohydrate improves
protein utilization, while lowering energy intake to a level below the amount needed
causes increased protein losses and breakdown. Therefore, one of the best ways to make
certain protein status is OK is to make certain enough total energy is consumed to
maintain activity and growth requirements.
The timing of protein ingestion is important as well as the amount to support muscle
synthesis. It’s essential to consume protein before, during, and after exercise to
stimulate muscle synthesis (Tipton & Wolfe, 2004).
Muscle is approximately 70% water and only about 20% protein. Therefore, increasing
muscle mass requires extra water, extra energy in the form of carbohydrates (to
maintain the needs of that extra muscle), and a little extra protein. In fact, for an athlete
increasing muscle mass at an extraordinarily high rate of 1 kg/week (2.2 lbs of extra
muscle per week); only 4 extra ounces of meat per day would be needed. The RDA for
protein is 0.8 grams/kg of body weight/day. Adequate energy intake primarily from
carbohydrates should ensure a positive protein balance in the muscle.
Most experts agree that additional protein can be easily obtained through a balanced
diet. High sources of protein include meat, poultry, fish, and eggs. However, vegetarians
can obtain adequate protein by combining non-meat items. For instance, combining
legumes (beans) and cereals (rice or corn) creates a protein combination of high quality.
However, animal proteins provide numerous other nutrients (including iron and zinc) that
are more difficult to obtain elsewhere unless the diet is very carefully planned.
Are there gender differences for protein requirements?
Little is known about gender differences in protein consumption and utilization, perhaps
because most athletes consume adequate amounts of protein regardless of gender
(Rosenbloom, 2006).
What are the effects of protein on athletic performance?
Team sports: In team sports athletes should not have difficulty meeting their protein
needs through eating a variety of protein rich foods. When athletes wish to increase the
muscle mass the protein intake should be adjusted accordingly (Murray and Horswill,
1997).
Short duration high intensity sports: Protein consumption for strength trained
athletes may be as high as 1.6 – 1.7 g/kg of body weight (American Dietetic Association,
2000). Athletes who restrict nutrient intake to lose weight for competition such as
boxers, figure skaters and wrestlers, may have inadequate protein intake and this can be
a limiting factor on performance (Murray and Horswill, 1997). Low intake of protein over
a long period adversely affects muscle mass.
Long duration moderate intensity sports: According to Murray and Horswill (1998),
the endurance athlete might have a higher protein requirement to maintain nitrogen
balance than the anaerobically trained athlete. The American Dietetic Association
recommends protein intakes between 1.2 – 1.4 g/kg of body weight for endurance
athletes (2000). This amount should easily be consumed as part of a balanced diet
without the use of supplements.
Micronutrients Needs (vitamins and minerals)
What are the vitamin and mineral requirements of athletes?
Vitamins and minerals play an important role in the metabolism of protein, carbohydrate
and lipids and in muscle function. Vitamins serve as a cofactor with specific enzymes that
regulate metabolic pathways and the synthesis of specific tissues (Murray and Horswill,
1997). Some studies recommend increased amounts of vitamins and minerals to balance
the extra energy and metabolic demands that athletes experience, however this has
been the source of some debate. (Refer to nutrition web sites for detailed information.)
Are there gender differences for micronutrient requirements?
All athletes need to consume at least the recommended daily allowance (RDA) of
vitamins and minerals. According to Akabas and Dolins (2005), many female athletes fail
to consume optimal amounts of some vitamins and minerals. Two micronutrients of
special concern are calcium and iron. Calcium is essential not only for strong bones, but
for muscle contractions and maintaining cells and connective tissue in the body as well.
Consuming adequate amounts of calcium can help alleviate muscle cramps. Iron
deficiency anemia reduces performance by limiting the amount oxygen that can be
delivered to the muscles, which can reduce aerobic performance (Ekblom, 1997).
Do athletes benefit from increased vitamin and mineral intakes?
Some research does not support the rationale that athletes who are in heavy training
need to increase vitamin requirements (Vander Beek, 1985; Fogelholm et. al., 1993;
Murray and Horswill, 1997; Akabas & Dolins, 2005). According to Murray and Horswill
(1997), recommendations for increasing vitamin intake in athletes have been established
for individuals with inadequate levels of these nutrients. For example, athletes recovering
from illness and injury may be deficient in trace elements and may need to increase their
intake of vitamins and minerals.
Team sports: According to Sobal, (1994) many athletes in team sports perceive the
need to supplement their diets and therefore add vitamin and mineral supplements at
mealtimes. However with a balanced diet, most team athletes can maintain optimal
levels of micronutrients.
Short duration, high intensity sports: According to Fogelholm (1993), athletes who
consume a diet which contains a variety of food sources should satisfy their nutritional
needs and therefore they should not need vitamin supplements (American Dietetic
Association, 2000); however, during competition some athletes may develop deficiencies
in the vitamins A & C, the B vitamins, thiamin, vitamin B6, riboflavin, and niacin
(Fogelholm, 1993).
Long duration, moderate intensity sports: Nieman et al. (1989) and Gabel et al.
(1995) have suggested that most endurance athletes should supplement their diet with
vitamins. However, the American Dietetic Association (2000) and Murray and Horswill
(1997) suggest that as long as the athlete is meeting the adequate dietary needs by
eating a wide variety of foods, the vitamin intake should be sufficient.
Special Nutritional Situations
The Vegetarian Athlete
Diets for vegetarian athletes should be formulated to take into consideration the effects
of both vegetarianism and the type of sport performed. While vegetarianism does not
necessarily mean reduced energy intakes, the elimination of meat and dairy from the diet
as well as high intakes of low-energy dense foods may place the vegetarian athlete at an
increased risk for low energy, protein, and micronutrient intakes (American Dietetic
Association, 2000). Monitoring body weight and composition is the preferred way to
determine fi energy needs are being met. To help avoid deficiencies vegetarian athletes
should consult with a Registered Dietician to ensure optimal nutrient intake levels.
Weight Management
Athletes may want to decrease or increase their weight for a variety of reasons. Body
weight not only affects an individual’s appearance, it can influence an athlete’s speed,
endurance and power (American Dietetic Association, 2000). If weight change is desired,
it should start slowly before the competitive season.
Weight can be gained by incorporating 500-1,000 kcals per day into the diet (American
Dietetic Association, 2000). Increased energy intake should be done in conjunction with
increased strength training to maximize muscle development. How quickly an athlete
gains weight will depend on genetics.
Athletes who wish to lose weight should do so with the guidance of a Registered Dietician
in order to optimize health and performance. Athletes who restrict energy intake or use
severe weight loss strategies are at greatest risk for nutrient deficiencies (American
Dietetic Association, 2000). Athletes should consume at least the RDAs/RDIs for all
nutrients from food. Healthy diet with reduced energy intake can promote weight loss of
approximately 1 to 2 lbs/week. However, many factors play a role in how quickly weight
loss will occur, including genetics, type of sport played, and foods eaten.
Some weight management strategies include setting and monitoring goals (American
Dietetic Association, 2000; Manroe, 1996). Some strategies to accomplish this include:

Setting realistic weight and body composition goals

Focusing on healthful habits such as stress management and making healthy
food choices, focus less on the scale

Monitoring progress by measuring changes in performance and energy level, and
general overall well-being

Developing lifestyle changes that will maintain a healthy weight for you, not your
sport

Not skipping meals or letting yourself get too hungry

Making sure dietary intake goals are realistic; don’t deprive yourself

Identifying dietary weaknesses and make a plan to deal with the