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FUELING
FOR PERFORMANCE
UNDERSTANDING AN ATHLETES NUTRIENT NEEDS
by Kathleen A.
Gould - Clinical Assistant Professor,
Towson University
Introduction
Athletes, who wish to compete at the
highest level strive to have the best
training and equipment to excel at their
sport. Often however, both athletes
and coaches neglect to focus on the
impact that nutrition can have on athletic
performance. Appropriate food intake
is either misunderstood or completely
ignored in formulating the ideal training
regimen. Frequently, the athlete will
focus on protein intake and ignore other
essential nutrients. In addition, many
athletes feel that it is necessary to
rely on supplements instead of healthy
foods to meet their nutritional needs.
The goal of this article is to present
how the body fuels physical activity,
and discuss the role that appropriate
food intake has in this process. Specific
recommendations for carbohydrates, proteins,
fats, minerals, vitamins, and fluids
will be provided.
Fuel for Muscle Work
Every cell in the body depends on a
constant supply of ATP
for energy. The amount of ATP that is
stored in the muscle is adequate to
provide for 2-4 seconds of work. Once
this supply is exhausted the muscles
replenish ATP by using the Phosphocreatine
system. This system uses the high
energy compound, phosphocreatine,
to regenerate ATP from ADP, and allows
for an additional minute of muscle work.
However, most athletes require more
than one minute of muscle work to accomplish
their goals and the body depends upon
both anaerobic
and aerobic
metabolism to generate additional ATP.
In both anaerobic and aerobic metabolism
glucose
is the fuel source that most readily
generates energy. This glucose comes
primarily from glycogen that is stored
in the muscle and liver, or it is provided
by carbohydrates which are supplied
by the diet. An adequate supply of carbohydrates
in the diet will promote glycogen storage
and prevent its depletion and therefore
potentially enhance performance. If
the diet is inadequate in carbohydrates,
lean body mass or muscle may be broken
down to generate glucose.
Carbohydrate Needs
An adequate supply of carbohydrates
in the diet is essential to maximize
athletic performance, and should make
up 50 to 65% of an individual’s
total daily calories. In other words,
if an athlete requires 2400 calories
to maintain their body weight, a minimum
of 1200 calories should come from carbohydrates.
This is equivalent to a minimum of 300
grams of carbohydrates daily.
The distribution of carbohydrates
throughout the day can also have an
effect on athletic performance. An athlete
needs carbohydrates before exercise,
to keep blood glucose in the right range,
and to top off glycogen
stores. It is best to take in sources
that are low in fat and fiber and easy
to digest. How much the athlete eats
is related to how soon they are going
to exercise. Larger amounts of carbohydrates
can be consumed 3-4 hours prior to exercise,
while smaller amounts are recommended
immediately prior to exercise. For example
one would not want to consume a pasta
dinner immediately before a game or
practice, but a banana and some sports
drink immediately prior is appropriate.
Carbohydrates are important during exercise
in order to prevent blood sugar from
dropping and fatigue from setting in.
Easy to digest sources such as sports
drinks and gels were designed for this
purpose, especially for the athlete
who is performing or working out for
more than an hour.
Immediately after practice or competition
is the best time for the muscle to uptake
glycogen. Carbohydrates that are consumed
in the first 15-30 minutes after activity
are readily available to rapidly replace
the glycogen that was depleted. These
carbohydrates can be supplied by sports
bars or with conventional foods such
as juice, starches or dairy products.
In fact low-fat chocolate milk has demonstrated
good results as a post workout recovery
drink when compared to sports drinks
in competitive cyclists (Karp, 2006).
The athlete’s selection should
be based on personal preference and
food availability immediately after
exercise. The ideal amount of carbohydrates
at this time is 1.1 grams per kilogram
of body weight. For example, an athlete
weighing 150 pounds (68 kg.) requires
about 75 grams of carbohydrates after
a heavy workout. Sixteen ounces of low-fat
chocolate milk (50 grams) and a low
fat granola bar (22-29 grams) meet this
need.
Fat Needs
Fat is an essential component of a healthy
diet because it is an important source
of energy. Between 20-35% of total calories
should come from fat for a total of
55-90 grams daily. Healthy fats come
from plant sources and are unsaturated,
while unhealthy fats are in animal foods,
fast foods, and commercial baked goods.
Fat intake should be minimized prior
to, during, and immediately after practice
or events because fat increases the
time for digestion and absorption of
carbohydrates. This delay inhibits the
rate that carbohydrates can replenish
blood glucose and glycogen stores.
Protein Needs
The major role of protein
is in tissue maintenance and repair
rather than as a source of energy or
calories. Therefore, athletes have a
slightly higher daily protein requirement
than sedentary individuals. The recommended
intake ranges between 1.1-2.0 grams
per kilogram of body weight per day.
Amounts in excess of 2 grams per kilogram
of body weight have no benefit because
the ability to build muscle is maximized
at this level. Using this range, a 150
pound (68 kg.) athlete requires between
75-136 grams of protein daily. The lower
end of the range is appropriate for
recreational athletes who exercise 10-12
hours per week, the middle of the range
is for those who train 12-20 hours per
week and the upper end is for elite
athletes training and competing more
than 20 hours per week.
For the most part these protein needs
can be met by consuming adequate amounts
of lean meat, fish and dairy products.
For example, four ounces of chicken
contains 28 grams of protein and eight
ounces of fat free milk contains 8 grams
of protein. Good plant sources of protein
include beans and nuts, with ½
cup of beans containing about 15 grams
and ¼ cup of nuts providing 5
grams of protein. Complete or complementary
protein sources should be consumed throughout
the day rather than all at once to assure
that essential amino acids are always
available. Consuming protein 2-4 hours
prior to exercise helps maintain a feeling
of fullness. However, excess protein
intake increases the fluid needs of
the athlete and therefore increases
the risk of dehydration.
Protein supplements, while not necessary,
may be utilized if the diet is inadequate.
Supplements containing combinations
of carbohydrates and proteins may be
used for repletion after exercise if
appropriate food sources are not readily
available. Consuming between 15-25 grams
of protein in combination with carbohydrate
within 15-30 minutes of exercise may
help recovery. Sixteen ounces of low-fat
chocolate milk and a granola bar will
supply about 19 grams of protein and
75 grams of carbohydrates.
Fluid Needs
Adequate hydration is essential to maintain
fluid volume and supply muscles with
oxygen and nutrients. The athlete must
remain hydrated before during and after
exercise in order to maximize performance.
A good indicator of hydration is urine
color with the goal being a pale straw
color. The recommended amounts of fluid
to avoid dehydration are as follows:
- 2 cups of fluid 2 to 3 hours prior
to exercise
- 1 cup 10 to 20 minutes prior to
exercise
- 1 cup every 10 to 20 minutes during
exercise
- 2 cups for every pound lost in
activity
Hydration can be achieved with the
use of sports drinks or water depending
on the duration of the activity. Water
is recommended for activities that are
one hour or less while sports drinks
should be utilized for longer events.
Sports drinks provide replacement of
both carbohydrates and electrolytes
during extended activity.
Energy Needs
Calorie needs of an athlete are widely
variable and depend on size, growth,
gender, and level of physical activity.
There are numerous formulas that estimate
caloric need based on age, size, gender,
and activity level. In general these
estimates suggest that a female athlete
requires between 2000 and 3000 calories
while a male athlete needs between 3000
and 5000 calories. The ability to maintain
an appropriate body weight is the best
indicator of an adequate caloric intake.
If an athlete is losing weight it is
likely that both body fat and muscle
are being lost and more calories are
needed. Undesired weight gain on the
other hand suggests that excessive calories
are being consumed.
Vitamin and Mineral Needs
Increased sweating and energy needs
increase the need for certain vitamins
and minerals. However, often additional
calorie intake will meet these needs
in a well balanced diet. The vitamins
that have an increased need are the
B complex, C, and E. The B complex vitamins
are readily obtained from eating grains,
Vitamin C comes from fruits and vegetable
and Vitamin E comes from nuts and oils.
The minerals which increase are iron,
calcium, sodium
and potassium.
Iron
is particularly important for the female
athlete and can be obtained from meat
and fortified cereals. Calcium is also
a concern and should come from dairy
products and fortified products such
as orange juice. Female athletes may
require supplemental iron and calcium
if they are not meeting their needs
with the diet.
Sodium
is in ample supply in most diets and
is obtained from processed foods and
sports drinks. Potassium
can be obtained also from fruits, vegetables,
and sports drinks. A multivitamin offering
no more than 100% of the RDA could be
consumed as an insurance policy if desired
for the athlete.
REFERENCES
American
College of Sports Medicine http://www.acsm.org
Dunford,
M.(ed.) (2006) Sports
Nutrition:A Practice Manual for Professionals.
(4th ed.) Chicago: American Dietetic
Association
Fink,
H.H., Burgoon, L.A., Mikesky, A.E. (2006)
A Practical Guide to Sports Nutrition.
Toronto: Jones and Bartlett.
Karp,
J.R., Johnston, J.D., Tecklenburg, S.,
Mickleborough, T.D., Fly, A.D., Stager,
J.M. (2006) Chocolate
Milk as a Post-Exercise Recovery Aid.
Sports Nutrition and Exercise Metabolism.
16(1),78-91.
Sports
Dietitians of Australia http://www.sportsdietitians.com.au
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