Recovery foods may be too sugary for athletes

Intake of carbohydrate-rich foods just after exercise is crucial for the body's recovery. Glycogen, the carbohydrate stored in the liver and muscles, is used up during exercise and prolonged exercise can lead to a decline in blood glucose concentration.

But foods and beverages designed to replenish and restore glycogen after exercise may need to be lower in sugar than those aimed at pre-exercise periods.

Taste and flavour has already been shown to be key for successful rehydration. Athletes, requiring proper rehydration, have been found to consume greater amount of fluids that they prefer than fluids that they dislike.

Now Japanese researchers report that rats studied after an exercise regime preferred lower sucrose concentration than before exercise. This supports anecdotal evidence that athletes have a temporary increase in the perception of sweetness after exercise and that a beverage that they prefer before exercise is too strong during as well as after exercise.

Foods lower in sugar would help athletes who find it difficult to consume enough nutrients to recover after exercise.

The team from the University of Health and Sport Sciences in Osaka, Japan tested responses to sweetened fluids after exercise in male rats. Ten male rats were individually housed with a selection of water or one of two sucrose solutions (0.4 per cent in study one; or 4 per cent, consumed before exercise, in study two). The bottles were arranged enabling the rats to drink both water and the sucrose solution at will.

The rats ran on a treadmill 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.

The researchers found that sucrose ingestion did not increase significantly after exercise in study one, where the 0.4 per cent sucrose solution was available, but it decreased in study two.The results raise the possibility that the sucrose concentration which rats favour changes after exercise, said the researchers.

They suggest that a possible rise in opioid peptide, such as endorphins, due to exercise might have led to the decreased intake of 4 per cent sucrose solution which rats had preferred.

While this study did not measure endorphin levels in blood, opioid-receptor antagonists are known to decrease intake of sweet solution in rats, as well as reduce highly preferred food and increasing intake of non-preferred food.In human studies, opioid antagonists have also been shown to reduce pleasurable food ratings and especially intake of foods with high preference ratings before administration of opioid antagonists.

The findings will be presented at the American Physiological Society's​ (APS) annual scientific conference, Experimental Biology 2004, at the Washington Convention Center this week.