When it comes to hydration, water seems like the obvious choice. But is it truly the most hydrating beverage? According to a recent scientific study, milk scores higher on the hydration index than water.

Milk vs. water for hydration

The surprising finding was discovered via a study that compared hydration from different beverages by analyzing fluid retention levels in the hours after drinking. Shockingly, both whole cow’s milk and skim milk were found to be among the most hydrating beverages—even surpassing mineral water in some conditions.

How is this possible? The explanation can be found in the nutritional composition of milk. “Milk contains natural sugars, proteins, and fats,” the study notes. “These nutrients slow the emptying of the stomach, helping the body retain fluids longer.”

What makes milk so hydrating?

Here’s a deeper look at makes milk more hydrating than water:

• Milk has a high electrolyte content (including sodium and potassium), which helps the body retain fluids.
• Milk contains protein and carbohydrates, which slow digestion, prolonging the presence of water in the body.
• Milk balances osmolarity, which promotes water absorption by cells.

Should we be drinking milk instead of water then?

This is not to say that we should all be filling our Stanleys with milk instead of water; H20 still remains the most recommended drink under normal conditions, and experts recommend drinking at least 8 oz a day. That said, the research indicates that there are times when milk can be more effective for hydrating.

• After strenuous physical activity, to replenish fluids and nutrients.
• For children and the elderly to promote more complete hydration.
• In periods of mild dehydration, when fluids need to be better retained.

In other words, milk can be a useful beverage for hydration in specific situations where retaining more fluid is important. Otherwise, stick to water most of the time.

Lactose intolerant? Stick to water

Obviously, those who are lactose intolerant, have special digestive conditions, or follow a plant-based diet should just stick with water. While some plant-based drinks (such as soy or oat milk) may offer a good compromise, they do not achieve the levels of hydration that cow’s milk offers.

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