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Is warm or cold water better to drink?
During Interbike, Camelbak showed a lot of flasks designed to keep liquid cold for longer. This concept both gels and conflicts with reputable sources, e.g. cold water gets into the intestines faster, but water is not absorbed there until it hits body temperature.
With summer approaching here, what does the latest research say? And does the fact that I would prefer to drink icy water on a hot ride (and therefore more of it) outweigh my body’s ability to absorb it (if cold water indeed, hydrates slower)?
— Christopher, Canberra, Australia
Please bring along a cold beverage, water or a sports drink, on your next hot ride. As you are aware, stomach or gastric emptying is one of the critical steps in assuring rapid fluid, carbohydrate, and electrolyte replacement.
One study published in the International Journal of Sport Nutrition and Exercise Metabolism compared the gastric emptying rates of 4 solutions that all contained a 6-percent carbohydrate concentration, and which were either one (glucose or fructose) or two carbohydrate (glucose +fructose, or sucrose) solutions. Sports drinks typically range at 6-8-percent carbohydrate concentration.
The test solutions were ingested at 12 degrees Celsius. There were no significant differences in gastric emptying or gastric volume between the solutions. The temperature within the stomach dropped from 36.5 degrees C to 23.3 degree C immediately after the beverages were ingested. However within 5 minutes, the cold beverages were warmed to 30 degrees C in the stomach. The effect of a cold beverage on gastric emptying is likely to be negligible since the solutions are warmed so quickly. So have the more palatable cold beverage, as you are likely to drink more and therefore match or minimize fluid loss from sweat.
Of course intestinal absorption is another piece of the equation in regards to fluid, carbohydrate, and electrolyte absorption. Since fluid is warmed in the stomach, it can be assumed that this is not a factor in intestinal absorption. What does seem to have the more effect is the type or number of carbohydrate sources in the drink consumed. Recent research has shown that having a carbohydrate mix, such as glucose + fructose, rather than just glucose alone.
One study compared two such beverages. Ingestion of glucose + fructose resulted in high rates of carbohydrate burning and fluid availability than a glucose only beverage, when subjects cycled in the heat. A follow-up study looked at the effects of varying drinks on performance. Ingestion of a glucose + fructose drink led to an 8-percent improvements in cycling time trial performance when compared to the ingestion of glucose alone. You might also want to consider that the sodium in sports drinks also helps pull the fluid through the small intestine when compared to water alone.
So you should not only make sure that your drink is cold (because it is more palatable in hot weather), but have a sports drink that has multiple carbohydrate sources, with the research pointing towards glucose + fructose as the best option. Having multiple carbohydrates can increase carbohydrate absorption to 1.3 g/kg body weight per hour versus just 1 g/kg per hour with glucose alone. Drink on a schedule and start drinking early on during your training ride. Once you become dehydrated gastric emptying will slow down. Having more volume can also stimulate gastric emptying, and gastric emptying can slow down at higher intensities, though the carbohydrate consumed in the sports drink improves performance.
Monique Ryan, MS, RD, LDN is a nationally recognized nutritionist with over twenty-four years of experience and is owner of Personal Nutrition Designs, a Chicago based nutrition consulting company that provides nutrition programs for endurance athletes across North America.