Heavy exercisers lose sweet appeal
Scientists in Japan show how a preference for a sucrose solution
was reduced in rats that had undertaken extensive exercise. Their
findings could have wider implications for food makers developing
foods to meet the post-exercise taste and nutritional needs active
consumers.
Presenting their findings at a meeting of the American Physiological Society, Koji Okamura and colleagues from the Exercise and Nutrition Laboratory at Osaka University in Japan conclude that the human preference for sweetness decreases after exercise.
"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," report the researchers.
For the study, the scientists used two tests using different concentrations of sucrose (sugar). Ten male rats were individually housed in a cage equipped with two bottles containing distilled water or a sucrose solution (S, 0.4 per cent, threshold for sweetness in study 1; or four per cent, consumed before exercise, in study 2).
The rats ran on a treadmill at 30 m/min for two hours. Water and sucrose consumption was measured on the day of exercise as well as before and the following day for six hours with two hour intervals. No food was given during the six hour timeframe.
In study 1, the rats' preference for the 0.4 per cent sucrose solution showed no change after exercise. In study 2, before exercise the rats showed a preference for the 4 per cent sucrose solution. However, after exercise the 4 per cent solution was not favoured by the rats and ingestion of the 4 per cent sucrose solution decreased.
"The results raise the possibility that the sucrose concentration which rats favour changes after exercise, since the amount ingested did not change in 0.4 per cent solution while it decreased substantially in the four per cent solution," say the authors.
They suggest the possibility that exercise increases the levels of endorphins, which can raise opioid peptide concentrations in the brain and suppress the intake of foods with high pleasurable ratings.
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 - glycogen lost during exercise.
For active consumers foods may need to be specially developed with the desired sweetness and carbohydrate levels to offset the effect of exercise-induced anorexia.
