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MONDAY, APRIL 19, 2004
Contact: Donna Krupa
703.967.2751 (cell)
703.527.7357 (office)
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APS Newsroom: April 17-21, 2004
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The Preference For Sweetened
Foods May Decline After Exercise
Washington, DC – Professional sports are more popular than ever
and involve both males and females. “March Madness,” track and field, and
golf all offer equal excitement for athletes of both genders. The
opportunities for sports excellence have never been better. At the same
time, the professional athlete’s body has never worked harder and the need
for post-exercise nutrition has never been greater.
Background
Scientists are aware that there is a decrease in glycogen content in the
liver and skeletal muscles following exercise. Prolonged exercise can lead
to a decline in blood glucose concentration. Thus it is important to ingest
carbohydrates after exercise in order to replenish and restore glycogen.
Fluid replacement is also crucial to avoid severe dehydration, and
factors such as taste and flavor have been shown to be keys for successful
rehydration. (It has been shown that athletes consumed greater amount of
fluids that they prefer than fluids that they dislike.) It is known that
tastes, which stimulate voluntary fluid intake during and/or after exercise,
include saltiness and sweetness.
Fluids designed for physical exercise situations contain carbohydrates to
supply energy. But after exercise, athletes have demonstrated a preference
for salt, as well as a temporary increase in the perception of sweetness.
Anecdotally, athletes occasionally quote that sweetness of a beverage that
they prefer before exercise is too strong during as well as after exercise.
These comments seem to support the idea that animals, too, may become
sensitive to sweetness or the taste of carbohydrates following exercise. If
this notion is true, then it could be a starting point for developing foods
and supplements that meet the post-exercise taste and nutritional needs of
the competitive female and male athlete.
A New Study
To test the hypothesis, a team of Japanese researchers has attempted to
determine responses to sweetened fluids after exercise in male rats. The
authors of “Preference for Sweetness May Decrease after Exercise in Rats,”
are Koji Okamura, Kayo Ikeda, and Yachiyo Harada, all at the Exercise
Nutrition Laboratory Graduate School of Sport Sciences, Osaka University of
Health and Sport Sciences Osaka, Japan. They will present their findings at
the American Physiological Society’s (APS) (www.the-aps.org)
annual scientific conference, Experimental Biology 2004, being held
April 17-21, 2004, at the Washington, D.C. Convention Center.
Methodology
The research consisted of two tests utilizing different concentrations of
sucrose (sugar). Ten male rats were individually housed in a cage equipped
with two bottles containing distilled water (W) or a sucrose solution (S,
0.4 percent, threshold for sweetness in study 1; or four percent, consumed
before exercise, in study 2). The bottles were arranged enabling the rats
to drink both water and the sucrose solution at will.
The rats ran on a treadmill at 30 m/min for two hours. Water and sucrose
consumption was measured on the day of exercise (Ex) as well as before (Pre)
and the following (Post) day for six hours with two hour intervals. No food
was given during the six hour timeframe.
Results
The researchers found that:
-
sucrose ingestion did not
increase significantly in study 1 (where the 0.4 percent sucrose solution
was available at the threshold for sweetness);
-
the preference for 0.4
percent (threshold) sucrose solution showed no change after exercise; and
-
sucrose ingestion
decreased in study 2 (consumption of the four percent sucrose solution
decreased after exercise).
The results raise the possibility that the sucrose concentration which
rats favor changes after exercise, since the amount ingested did not change
in 0.4 percent solution while it decreased substantially in the four percent
solution.
Caveat
Scientists have known that opioid-receptor antagonists decrease intake of
sweet solution in rats, as well as reduce highly preferred food and
increasing intake of non-preferred food (standard laboratory chow). In human
studies, opioid antagonists have been shown to reduce pleasurable food
ratings and especially intake of foods with high preference ratings before
administration of opioid antagonists. Exercise is also known to increase
β-endorphin levels. While this study did not measure β-endorphin levels in
blood, a possible rise in opioid peptide due to exercise might have led to
the decreased intake of four percent sucrose solution which rats had
preferred.
Conclusions
The authors conclude that preference for sweetness decreases after
exercise and the sweetness level preferred before exercise is insufficient
to restore exercise-induced anorexia in rats. Because early ingestion of
carbohydrates is effective after exercise in recovering skeletal muscle
glycogen expended by exercise, the production of foods with a desired
sweetness level and carbohydrates would provide a significant step in
offsetting exercise-induced anorexia. This would benefit all athletes who
experience difficulties to consume enough nutrients to recover after
exercise.
- end -
The
American Physiological Society (APS) was founded in 1887 to foster basic and
applied science, much of it relating to human health. The Bethesda, MD-based
Society has more than 11,000 members and publishes 3,800 articles in its 14
peer-reviewed journals every year.
***
Editor’s
Note: For further information or to schedule an interview with a member of
the research team, please contact Donna Krupa at 703.967.2751 (cell),
703.527.7357 (office) or at
djkrupa1@aol.com. Or contact the APS newsroom at 202.249.4009 between
9:00 AM and 6:00 PM EDT April 17-21, 2004.
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