Which drink is best for hydration? Hint: It isn’t water

A study from Scotland's St. Andrews University found that water isn't the most hydrating drink. The researchers found that while water, both still and bubbling, hydrates rapidly, beverages with a little sugar, fat, or protein keep us hydrated longer.

Nutrient content also affects hydration. Milk is more hydrating than water because it contains lactose, protein, and fat, which impede stomach emptying and prolong hydration.

Milk is more hydrating than water

Milk provides salt, which absorbs water and reduces urine production. Diarrhea oral rehydration solutions are similar. Sodium, potassium, and a little sugar assist the body retain water.

“This study tells us much of what we already knew: Electrolytes—like sodium and potassium—contribute to better hydration, while calories in beverages result in slower gastric emptying and therefore slower release of urination,” said Melissa Majumdar, a registered dietitian, personal trainer, and Academy of Nutrition and Dietetics spokeswoman who was not involved in the study.

Sugar in moderation

It gets tricky here: Fruit juices and colas are not as hydrating as lower-sugar drinks. They take longer to empty than water, but osmosis dilutes their high sugar content in the small intestine. The body "pulls" water into the small intestine to dilute these beverages' sugars. Anything in the intestine is outside your body.

Majumdar explained that juice and soda are less hydrating and contain more sugars and calories than solid foods. Always choose water over soda for hydration. Water keeps skin moist and helps the kidneys and liver eliminate pollutants. It's cheap.