Can Milk Hydrate You as Well as Water? The Surprising Scientific Findings

January 3, 2026 •

4 min read

Recent studies from Scotland's St. Andrews University indicate that milk can be more effective for sustained hydration than plain water. This surprising discovery challenges the long-held assumption that water is the gold standard for rehydrating, raising the question: can milk hydrate you as well as water, or even better?

Quick Summary

Milk's unique nutrient profile, featuring natural sugars, proteins, fats, and electrolytes, helps the body retain fluids longer than plain water, particularly after strenuous activity. Its slower digestion prevents rapid fluid loss through urination, making it a powerful rehydration tool.

Key Points

Superior Post-Exercise Hydration: Studies indicate milk is more effective for sustained rehydration after intense workouts than water or sports drinks.
Nutrient-Enhanced Retention: Milk's natural proteins, fats, and electrolytes, including sodium and potassium, help the body absorb and retain fluid for a longer duration.
Slower Fluid Release: The slower gastric emptying rate of milk provides a steady rehydration effect, preventing the rapid fluid loss experienced with water.
Protein and Electrolyte Boost: Milk offers the added benefit of high-quality protein for muscle repair and replenishes vital electrolytes lost through sweat.
Water is Still Key for Daily Hydration: For general, everyday hydration needs, water remains the best, calorie-free option.
Consider Calories: The higher calorie content of milk makes it less suitable for casual, constant thirst-quenching compared to water, especially for those monitoring their caloric intake.

The Science Behind Milk's Hydrating Power

While water is essential for daily hydration, scientific research has uncovered that for certain situations, milk may actually be superior for maintaining fluid balance over a longer period. This isn't because milk has more water—it is, in fact, mostly water—but because of its specific nutritional composition. The presence of key components slows down the body's processing of fluids, leading to more effective and prolonged hydration. This insight is particularly relevant for athletes and individuals recovering from significant fluid loss due to sweat or illness.

Why Milk Retains Fluid More Effectively

Several factors contribute to milk's hydrating properties:

Optimal Electrolyte Balance: Milk contains a natural balance of electrolytes like sodium, potassium, and calcium. These minerals help regulate fluid balance and assist the body's absorption of water. When you sweat during exercise, you lose electrolytes, and milk helps replenish them.
Slower Gastric Emptying: The fats, proteins (casein and whey), and natural sugars (lactose) in milk cause it to be digested and released from the stomach more slowly than plain water. This provides a slower, steadier supply of fluids to the body, preventing the rapid urination that can occur after drinking plain water.
Stimulates Water Retention: The sodium in milk acts like a sponge, encouraging the body to hold onto water. This mechanism, also used in oral rehydration solutions, is crucial for improving fluid retention and prolonging hydration.
Promotes Post-Exercise Recovery: For athletes, the carbohydrates in milk help replenish glycogen stores, while the protein aids in muscle repair and synthesis. This makes milk, and especially chocolate milk, a powerful all-in-one recovery beverage that addresses multiple post-workout needs simultaneously.

The Beverage Hydration Index (BHI)

In 2015, a study published in the American Journal of Clinical Nutrition introduced the concept of the Beverage Hydration Index (BHI). This index measures how well different beverages rehydrate the body based on fluid retention over a set period. In this research, skim and whole milk ranked higher than plain water, confirming that milk's nutrient density leads to better fluid balance. This provides a quantifiable measure that supports the anecdotal and observational data about milk's hydrating abilities.

Potential Drawbacks and Considerations

Despite its advantages, milk is not a one-size-fits-all hydration solution. For general, low-activity daily hydration, water is still the best option due to its lack of calories and simplicity. A glass of whole milk can contain around 150 calories, and regularly swapping water for milk could lead to unintentional weight gain. Furthermore, milk is not suitable for everyone. Individuals with lactose intolerance or milk protein allergies should avoid it and seek alternative rehydration methods. The natural sweetness in milk is not the same as the added sugars found in many commercial beverages, which can actually hinder hydration.

Comparison Table: Milk vs. Water for Hydration


Feature	Milk	Water
Gastric Emptying	Slower due to proteins, fats, and carbs.	Fast, leading to quicker fluid absorption.
Fluid Retention	Higher, thanks to electrolytes and slower digestion.	Lower; quicker urine output.
Key Nutrients	Electrolytes (Na, K, Ca), protein, carbs, fats.	None. Contains trace minerals if not purified.
Calories	High (varies by fat content); can be a consideration for weight.	Zero. Ideal for everyday, calorie-free hydration.
Best Use Case	Post-exercise rehydration and recovery.	General, daily hydration for all activity levels.
Cost	More expensive.	Free from the tap, cheapest option.

Conclusion: Making the Right Choice for Your Needs

The question of whether milk can hydrate you as well as water has a nuanced answer based on scientific findings. For athletes needing to replenish electrolytes, protein, and fluids after an intense workout, milk's unique composition makes it a highly effective and convenient choice for sustained rehydration. Its slower digestion and superior fluid retention mean you stay hydrated for longer compared to water or many sports drinks. However, for everyday, general hydration throughout the day, plain water remains the most practical, zero-calorie, and essential choice. The key is understanding your specific needs and choosing the beverage that best supports your hydration goals. Ultimately, milk is a potent tool for certain rehydration scenarios, but water is and will always be the foundation of a healthy hydration strategy. For those with special dietary needs, such as lactose intolerance, suitable alternatives exist. The takeaway is to diversify your fluid intake according to your body's demands and remember that both beverages have their place in a balanced diet.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before making significant changes to your diet or hydration strategy, especially if you have existing health conditions or dietary restrictions.

Milk as an effective post-exercise rehydration drink. (PubMed)

Frequently Asked Questions

Milk is more hydrating after exercise due to its composition, which includes water, electrolytes (sodium, potassium), proteins, and carbohydrates. These components slow down digestion, allowing the body to absorb and retain fluids for a longer period compared to plain water.

No, for general daily hydration, plain water is still the best choice. Milk is calorie-dense, and replacing all water intake with milk could lead to excess calorie consumption. Water is sufficient for normal hydration without the added nutrients that may not be needed.

Electrolytes like sodium and potassium in milk help regulate fluid balance and aid in the absorption of water more efficiently. Sodium, in particular, helps the body retain water, reducing the rate of urine production after drinking.

Studies have shown both skim and whole milk to be effective for rehydration, performing better than water based on fluid retention. The specific fat content affects calorie count but the electrolytes and other factors remain effective.

Yes, chocolate milk is often recommended as an effective post-exercise recovery drink. The additional carbohydrates from sugar can help replenish muscle glycogen stores, while the proteins assist in muscle repair.

Milk should not be used as the primary treatment for severe dehydration. In such cases, a healthcare professional should be consulted immediately. Milk is more suited for rehydration after moderate to intense physical activity or illness.

Individuals with lactose intolerance should avoid regular milk for rehydration. Lactose-free milk or other alternatives may be a suitable option, but those with allergies or intolerances should find alternative methods to rehydrate.