Importance
of Carbohydrate Consumption In Athletes
By:
Nicole
Plante
The consumer world has been swept
up in the low-carbohydrate diet whirlwind.
A rebirth of the diet revolution that Dr. Atkins created in 1972 has
brought back numerous books and headlines that are making claims about the
low-carbohydrate diet. The thought of an athlete eating a low carbohydrate
diet like the new consumer fad is quite frightening.
For
centuries athletes have relied on carbohydrates for their main energy source,
can they survive in a low-carbohydrate world?
Athletes
require more calories than a non-athlete to supply their body with adequate
energy for training activities. Carbohydrates
can supply up to 95% of your body’s energy during high intensity training
regimens, such as a high intensity exercise level well over your VO2 max that
can be sustained for 1-2 minutes (Williams, 2005). An
athletes VO2 max is the highest volume of oxygen consumed during exercise.
Carbohydrates
are stored in the body and are found as muscle glycogen, liver glycogen and
blood glucose. These are three very
important factors that can inhibit or enhance exercise performance.
The relationship with physical performance is muscle glycogen.
As it is being used during exercise blood glucose enters the muscles and
energy pathways. The liver will
then release some of its glucose to help maintain or elevate blood glucose
levels to prevent hypoglycemia (Williams, 2005).
Both hypoglycemia and depleted muscle glycogen may result in fatigue.
Whether this impairs performance may depend on the individual, but
prevention of hypoglycemia is one of the major objectives of carbohydrate
consumption (Williams, 2005). By
maintaining optimal levels of blood glucose, liver glycogen, and muscle
glycogen, through the supply of adequate levels of carbohydrates, an athlete can
assure a better level of exercise performance.
Coggan and Coyle (1987) suggested that the "primary mechanism of
delayed fatigue is maintenance of blood glucose and carbohydrate oxidation rates
during the latter stages of exercise, at which time muscle glycogen is
limited"(Davis & Brown, 2001). Basically stating that all three sources
of carbohydrate are essential in athletic performance.
With carbohydrates contributing largely to the body during exercise the
body will not be able to reach a high level of athletic performance without
adequate levels of carbohydrates. The
Atkins low carbohydrate diet only permits 20g of carbohydrate in its early
phase. If 130g of carbohydrate are
not consumed daily, the body will produce the glucose it needs primarily from
protein in the body (Williams, 2005). By
taking the glucose it needs for energy from protein your lean muscle tissue is
adversely affected. Over time an
athlete can experience negative effects in performance as far as explosiveness,
strength, and the ability to store muscle glycogen.
The process of this new formation of glucose in the body is referred to
as gluconeogenesis. To form glucose
through gluconeogenesis the body seeks out protein, which is broken down into
amino acids, where certain amino acids may be converted to glucose in the liver
(Williams, 2005). "A high
carbohydrate intake is necessary to restore muscle and liver glycogen stores to
ensure sufficient glucose availability for skeletal muscle contraction for
training on successive days" (Trivino, 2004, p. 2).
By maintaining adequate glycogen stores in the body from carbohydrates
your body doesn’t have to seek out protein to provide itself with energy.
Getting the necessary level of carbohydrate for athletic performance is
vital, enabling the athlete to keep the muscle that he/she has developed through
work.
Carbohydrate consumption before, during, and after exercise can help
maintain blood glucose during exercise, maximize exercise performance, and
improve recovery time (ADA, 2000). The
American Dietetic Association recommends that athletes consume 55-60% of their
total calories from carbohydrate on a daily basis.
A range of six to ten grams per kilogram of body weight is recommended,
the amount depends on the exercise or sport intensity.
It
is beneficial to consume a substantial amount of carbohydrates one to two days
prior to an event and to decrease the intensity of training to assure ample
glycemic support (Williams, 2005). Varied
results have been demonstrated through various research in regard to
carbohydrate intake within one to four hours prior to an intense workout,
prolonged exercise, or athletic event. Normally
with adequate muscle and liver glycogen stores carbohydrate supplements have not
been found to improve exercise performance in high-intensity exercise for 30-90
minutes. However, Jeukendrup &
el-Sayed, with their associates, recently reported that cyclists exercising for
approximately one hour at high-intensity significantly improved their
performance following ingestion of a carbohydrate supplement, as compared to a
placebo. It is possible in such a
case "that the ingested carbohydrate may help provide glucose to the
fast-twitch muscle fibers or prevent premature depletion in the slow-twitch
fibers" (Williams, 2001, p. 130). Welsh
& colleagues, reported that carbohydrate intake before and during exercise
resulted in significant improvements in various test of physical and mental
functions performed throughout an experimental trial of 60-90 minutes of
intermittent high-intensity exercise (Williams, 2001).
Toward the end of the 60 minute period, the carbohydrate trial resulted
in faster 20 meter sprint time, longer time to fatigue in a shuttle run,
enhanced whole body motor skills, and decreased self-reported perception of
fatigue. These results suggested a
beneficial role of carbohydrate-electrolyte ingestion on physical and mental
functions during intermittent exercise similar to that of many competitive team
sports (Williams, 2001).
Whether
to include carbohydrates during exercise has been an ongoing debate.
Traditionally, it was thought that consuming carbohydrates wasn't
necessary because you have enough glycogen to last about two hours of intense
exercise. Recently, researchers
have found that taking in carbohydrates and water may be more beneficial (Eberle,
2000). One particular study
analyzed cyclists who pedaled at 80% of their maximum for fifty minutes.
Cyclists who consumed six oz. of carbohydrate beverage were six percent
faster then those who consumed water, those who consumed 32 oz. were an
additional six percent faster (Eberle, 2000).
Williams, 2001, suggests that you should replenish every 15-30 minutes of
exercise. Your body uses 30-60g of
carbohydrate per hour, therefore consuming a 5-10% solution with about 15-20g of
carbohydrate every 15-20 minutes should be sufficient (Williams, 2001).
Such a beverage would be an 8oz. sports drink with approximately 14-18
grams of carbohydrate.
For an athlete to perform at optimal levels on subsequent occasions the
body needs to recover its glycogen stores and repair muscle tissue.
The recovery phase is an important time to consume carbohydrates.
After exercise an athletes muscles are highly insulin receptive which
enables the transport of glucose and amino acids into muscle cell and
stimulating glycogen and muscle protein also, greatly reducing the incidence of
protein breakdown (Goldberg, 2005). By
consuming carbohydrates within 45 minutes after exercise an athlete can repair
the body’s glycogen stores and muscle tissue.
This will subsequently improve the ability to perform the next time the
athlete exercises. A Vanderbilt
University study conducted by Levenhagen et. al, studied the effect of a
carbohydrate-protein supplement following a one-hour workout.
Subjects were given the supplement immediately after exercise and three
hours later. Protein synthesis in the body was nearly three times greater
when the supplement was taken immediately after the workout (Goldberg, 2005).
Taking advantage of proper nutrition as an athlete on a daily basis can
begin to have long-term benefits. In
a 12-week study subjects received a carbohydrate-protein mixture immediately
after each exercise session and two hours after each session.
Individuals who consumed their mixture immediately after exercise had an
8% increase in muscle size and 15% increase in strength.
There were no significant improvements in individuals who consumed the
mixture two hours later (Goldberg, 2005).
Carbohydrates play a fundamental role in athletic performance. Athletes cannot be swept up in the low-carbohydrate
whirlwind. They should be reminded
about the underlying facts that surround the benefits of carbohydrates.
An athlete cannot forget the importance of incorporating their increased
need for carbohydrates into a diet with adequate protein and fat.
Protein provides amino acids for building and repair of muscle tissue. When seeking optimal performance and significant gains in
workouts and competition a diet complete with carbohydrates, protein, and fat
are the key to success.
Reference List
Brown, Adrienne S. & Davis,
Mark J. Carbohydrates, Hormones,
and Endurance Performance. Sports
Science Exchange 14: 1-4.
Eberle, Suzanne Girard. Endurance
Sports Nutrition. Human Kinetics. (2000).
Goldberg, Paul. (2005). Recovery
Nutrition for Athletes. National
Strength & Conditioning Associations Performance Training Journal 3:
13-15.
Nutrition and athletic
performance-- Position of the American Dietetic Association, Dietitians of
Canada, and the American College of Sports Medicine.
Journal of the American Dietetic Association 100: 1543-1556.
Trivino, Geoff. Performance Detractors: Assessing the Low Carbohydrate Diet
and Its Effect Upon Athletic performance. (2004).
Williams, Melvin H. Nutrition
for Health, Fitness & Sport, 7th edition.
McGraw-Hill Companies, Inc. (2005).