Discover Which Kind of Milk is More Hydrating Than Water

October 25, 2025 •

4 min read

According to a study published in the American Journal of Clinical Nutrition, both skim and whole milk were found to be more hydrating than water over a four-hour period. This surprising finding reveals that a certain kind of milk is more hydrating than water, challenging our long-held assumptions about the best way to rehydrate.

Quick Summary

Skim milk and whole milk contain a hydrating blend of electrolytes, protein, and carbs that help the body retain fluid more effectively and for longer than plain water.

Key Points

Skim milk is most hydrating: Research shows skim milk is the most hydrating, scoring higher than water on the Beverage Hydration Index, with less fluid loss.
Electrolytes are key: Milk contains natural electrolytes like sodium and potassium, which help the body retain fluids more effectively than plain water.
Macronutrients matter: The protein and carbohydrates in milk slow down digestion (gastric emptying), leading to prolonged fluid absorption and less urine output.
Post-exercise is optimal: Milk is particularly beneficial for rehydrating after intense exercise, where the additional nutrients also support muscle recovery.
Water is for general hydration: Due to its caloric content, milk should not replace water for general daily hydration, but it complements it effectively.
Plant-based alternatives differ: Plant-based milks generally lack the full hydrating nutrient profile of dairy milk, offering less fluid retention.
Lactose-free works too: Lactose-free milk maintains the same hydrating properties as regular dairy milk, making it a good option for those with intolerance.

The Surprising Science Behind Milk's Superior Hydration

For decades, water has been seen as the undisputed champion of hydration. However, recent scientific research suggests that certain types of milk can be even more effective at rehydrating the body, particularly after intense physical activity. The secret lies not just in its water content, but in its unique nutritional profile. A 2016 study from St. Andrews University in Scotland developed a "Beverage Hydration Index" (BHI) to compare the hydrating effects of different drinks. The results, which have since been replicated, found that both whole milk and skim milk ranked higher on the BHI than plain water.

Electrolytes: The Fluid Regulators

Milk's high electrolyte content is a primary reason for its hydrating power. Electrolytes are essential minerals that play a crucial role in maintaining the body's fluid balance. When we sweat, we lose electrolytes, especially sodium and potassium. Replenishing these is key to effective rehydration.

Sodium: Helps the body retain water, acting like a sponge to prevent it from being immediately expelled as urine.
Potassium: The main intracellular cation, which is involved in restoring fluid balance inside the body's cells.
Other Minerals: Milk also contains other electrolytes like calcium, which support overall bodily function.

The Role of Macronutrients in Hydration

Beyond electrolytes, the macronutrients found in milk contribute significantly to its hydrating properties. The presence of protein and carbohydrates in milk slows down the digestive process, a phenomenon known as gastric emptying.

This slower release means that the fluids and electrolytes are absorbed more gradually over a longer period, resulting in greater fluid retention and less urine output compared to drinking plain water. Plain water is absorbed quickly, which can lead to a rapid increase in urine production and less overall fluid retention. This is why milk is particularly beneficial for rehydrating after a strenuous workout when sustained fluid retention is desired.

How Milk Compares: Dairy vs. Alternatives

Not all milk is created equal when it comes to hydration. The subtle differences in composition between skim, whole, and plant-based milks impact their effectiveness.

Skim Milk vs. Whole Milk

While both are highly effective, skim milk is often cited as being slightly more hydrating than whole milk. The difference comes down to their respective water content. Since skim milk has less fat, it has a slightly higher percentage of water by volume. This allows it to be processed a little more quickly by the body while still retaining the beneficial electrolytes and macronutrients that make it more hydrating than water. For individuals looking to maximize hydration with fewer calories, skim milk is the optimal choice.

Plant-Based Milk Alternatives

Plant-based alternatives like almond, soy, and oat milk also contribute to hydration due to their high water content. However, they generally do not offer the same superior hydration benefits as cow's milk because they lack the specific nutrient balance. While they can be fortified with calcium and vitamin D, most lack the natural levels of electrolytes, protein, and carbohydrates found in dairy milk that are essential for long-term fluid retention. Soy milk, due to its protein content, may offer more hydration benefits than other plant-based options but still does not match the full profile of dairy.

Beverage Hydration Comparison


Beverage	Primary Hydration Mechanism	Key Advantage	Calories	Post-Exercise Hydration?
Skim Milk	Electrolytes, Protein, Carbs	Best Fluid Retention	Moderate	Yes, superior
Whole Milk	Electrolytes, Protein, Carbs	Good Fluid Retention	High	Yes, excellent
Plain Water	High Water Content	Zero Calories	Zero	No, rapid excretion
Oral Rehydration Solution	Electrolytes, Sugar	Rapid Electrolyte Replenishment	Low	Yes, excellent
Sports Drink	Electrolytes, Sugar	Quick Electrolyte Replenishment	Low-Moderate	Yes, good

Practical Applications and Considerations

For most people in day-to-day life, plain water is still the best and most practical choice for staying hydrated. It contains no calories and is readily available. The superior hydrating properties of milk are most beneficial in specific situations:

Post-Workout Rehydration: After an intense exercise session where fluids and electrolytes are lost through sweat, milk provides a complete recovery drink. The protein helps with muscle repair, while the carbs and electrolytes aid in faster and more sustained rehydration than water or many sports drinks. Chocolate milk, in particular, is a popular recovery drink for athletes due to its optimal carbohydrate-to-protein ratio.
Specific Health Needs: For children, the elderly, or those recovering from mild illness, milk can offer more comprehensive hydration and nutritional support than water alone. The extra nutrients can be particularly beneficial for those who may not be eating regularly.
Maintaining Hydration Longer: For scenarios where you know you won't have access to fluids for a while, a glass of milk can help you stay hydrated for a longer period than water due to its slower gastric emptying.

However, it is crucial to consider the extra calories and potential for digestive issues, especially for those with lactose intolerance. Milk should be seen as a complement to, not a replacement for, water in a balanced diet. If you are lactose intolerant, lactose-free milk offers the same hydration benefits as regular dairy milk.

Conclusion

While water is the ideal fluid for general, daily hydration due to its zero-calorie nature, a certain kind of milk, specifically skim milk, has been scientifically shown to be more hydrating in certain contexts. Its potent combination of electrolytes (sodium, potassium), proteins, and carbohydrates slows down digestion and promotes longer fluid retention than water. This makes milk an excellent choice for rehydration, particularly after exercise, where the additional nutrients also aid in recovery. However, due to its caloric density, it should not be used as a total replacement for water for all fluid intake. Ultimately, understanding these differences allows you to choose the best beverage for your specific needs, leveraging milk's unique benefits for more effective rehydration when it matters most.

For further reading on the science behind the Beverage Hydration Index, consult the original research: The American Journal of Clinical Nutrition.

Frequently Asked Questions

Milk is more hydrating than water due to its combination of electrolytes (like sodium and potassium), protein, and carbohydrates (lactose). These components work together to slow the emptying of fluids from the stomach, allowing the body to absorb and retain the fluid for a longer period.

While both are more hydrating than water, skim milk is considered slightly more hydrating than whole milk. This is because skim milk has a higher water content due to its lower fat percentage, allowing for slightly faster absorption while retaining the key electrolytes and macronutrients.

No, you should not replace water with milk for daily hydration. Water is the best choice for everyday fluid intake as it has no calories. Milk is best reserved for specific situations, such as post-exercise rehydration, due to its higher caloric content.

Plant-based milks are primarily water and do contribute to hydration. However, they generally lack the specific balance of electrolytes, protein, and carbs that make dairy milk superior for prolonged fluid retention. Most research has focused on dairy milk's effects.

Yes, chocolate milk is often considered an excellent post-exercise recovery drink. It provides a balanced ratio of carbohydrates and protein, along with electrolytes, to replenish fluids and aid in muscle repair after a strenuous workout.

The best time to choose milk for hydration is after a sweaty or intense workout, when you need to replenish lost fluids, electrolytes, and macronutrients. Its slow absorption helps retain fluids longer than water alone.

Yes. Lactose-free dairy milk is available and offers the same hydration benefits as regular dairy milk. The removal of lactose does not compromise the electrolyte and protein content that makes it an effective rehydration beverage.

Yes, to a small degree. While both whole and skim milk are highly hydrating, the fat content in whole milk slows gastric emptying even more, meaning absorption might be slightly slower. For maximal hydration speed combined with retention, skim milk's lower fat content and slightly higher water concentration make it marginally more effective.

Less urine output after drinking indicates that the body is retaining more of the fluid for longer, rather than excreting it rapidly. In the context of milk, the electrolytes and nutrients promote this longer retention, helping maintain a more positive fluid balance over time compared to plain water.