Nutrition Diet: What has the highest rate of hydration?

October 12, 2025 •

4 min read

According to a study in The American Journal of Clinical Nutrition, beverages containing nutrients like milk and oral rehydration solutions can be more hydrating than plain water over a few hours. Understanding what has the highest rate of hydration requires looking beyond simple water to the science of nutrient absorption and retention.

Quick Summary

This article details the science behind rapid fluid absorption and compares the hydrating properties of various beverages and foods. It explores why some drinks can be more effective than water for specific rehydration needs, such as during illness or after intense exercise. The content covers the role of electrolytes, carbohydrates, and proteins in maximizing hydration.

Key Points

Oral rehydration solutions are most rapidly absorbed: Because of a process called sodium-glucose cotransport, ORS can rehydrate a person with moderate fluid and electrolyte loss faster than plain water.
Skim milk is more hydrating than water over time: The protein, fat, and lactose in milk slow down gastric emptying, resulting in lower urine output and longer fluid retention compared to water.
Electrolytes are crucial for optimal hydration: When fluid is lost through sweat or illness, electrolytes like sodium and potassium are also depleted. For effective rehydration, these minerals must be replenished along with water.
Water-rich foods contribute to your daily intake: Fruits and vegetables like cucumber, watermelon, and lettuce contain high water percentages and provide additional nutrients, supplementing fluid intake from beverages.
The best hydration method depends on your needs: For everyday hydration, plain water is sufficient. However, for rapid recovery from intense fluid loss or post-workout refueling, ORS, milk, or other electrolyte-enhanced drinks may be more effective.
Severe dehydration requires immediate medical attention: For critical dehydration, IV fluids are the fastest way to replenish fluids and electrolytes and should be administered by a healthcare professional.

Hydration is fundamental to all bodily functions, influencing everything from cognitive performance to metabolic processes. While most people reach for water when they're thirsty, the rate and efficiency of hydration depend on more than just the fluid's water content. The presence of electrolytes, carbohydrates, and proteins can significantly impact how quickly and how long the body retains fluid.

The science behind high-rate hydration

When you become dehydrated, your body loses both water and vital electrolytes, such as sodium and potassium. Drinking plain water helps restore fluid volume, but it doesn't replace these lost minerals. The secret to more effective rehydration lies in a process called sodium-glucose cotransport. In the small intestine, specific carrier proteins help transport sodium and glucose across the intestinal lining. This process draws hundreds of water molecules with it, significantly speeding up absorption.

Oral rehydration solutions (ORS)

This is why medical-grade Oral Rehydration Solutions (ORS) are so effective. Scientifically formulated to contain precise ratios of glucose and electrolytes, ORS can be absorbed faster than plain water, ensuring quicker recovery from moderate dehydration, especially that caused by vomiting and diarrhea. The World Health Organization and UNICEF have long advocated for ORS due to its high success rate in treating dehydration.

The surprising hydrating power of milk

Milk has been shown in studies to be more hydrating than plain water over a few hours. Skim and full-fat milk have a high Beverage Hydration Index (BHI), which measures fluid retention in the body. This is because milk's natural sugars (lactose), proteins, and fat help slow down the stomach's emptying rate. This results in a slower, more prolonged release of fluids and nutrients into the body, leading to less urine output and longer-lasting hydration. For athletes needing post-exercise recovery, milk offers fluids, electrolytes, and protein for muscle repair.

Comparing beverages: Beyond plain water

For daily hydration, water is the gold standard: it's accessible, affordable, and calorie-free. However, depending on the situation, other drinks may offer a hydration advantage. The following comparison table highlights the key differences between plain water, oral rehydration solutions, and milk in a post-exercise scenario, though benefits can extend to other situations involving fluid loss.


Feature	Plain Water	Oral Rehydration Solution (ORS)	Skim Milk
Best For	Everyday hydration, general fluid intake.	Rapid rehydration during illness (vomiting, diarrhea) or intense fluid loss.	Post-exercise rehydration, sustained hydration, nutritional boost.
Fluid Absorption	Absorbed relatively quickly, but lacks electrolytes to maximize cotransport.	Absorbed very rapidly due to precise balance of glucose and sodium.	Slower absorption due to fat, protein, and sugar content, leading to longer fluid retention.
Key Electrolytes	Low levels.	High levels of sodium, potassium, and chloride.	High levels of sodium, potassium, and calcium.
Nutritional Content	None.	Glucose, electrolytes.	Carbohydrates, protein, fat, calcium, and other vitamins.
Calorie Content	0 calories.	Varies by formulation, generally low to moderate.	Moderate calorie content from fat, protein, and carbs.
Best Practice	Sip continuously throughout the day.	Follow manufacturer's or doctor's instructions precisely to avoid side effects.	Ideal after a workout to replenish fluids, electrolytes, and energy stores.

Hydrating foods: The nutrient-rich option

Up to 20% of your daily fluid intake can come from food, and incorporating water-rich fruits and vegetables is a delicious way to boost hydration.

Cucumber: Composed of over 95% water, cucumbers are a refreshing, low-calorie snack packed with potassium and vitamin K.
Watermelon: With a 91% water content, this summer staple is also rich in antioxidants like lycopene and vitamins A and C.
Tomatoes: These contain about 95% water and are an excellent source of vitamin C and antioxidants.
Strawberries: High in vitamin C and fiber, strawberries are 91% water and make a great addition to smoothies or yogurt.
Lettuce and leafy greens: Romaine and iceberg lettuce both have water content exceeding 95% and provide a source of fiber and vitamins.
Broth-based soups: Soups and broths provide a significant amount of fluid, along with electrolytes like sodium and potassium, making them hydrating and nutrient-dense.

Putting it all into practice

Choosing the right hydration strategy depends on your circumstances. For healthy individuals engaging in daily activities, plain water remains the ideal choice for its simplicity and calorie-free nature. During periods of prolonged, intense exercise or significant fluid loss, such as with illness, an ORS or electrolyte-enhanced drink is a more efficient option. For sustained hydration, particularly after a workout, milk's unique nutrient profile can provide a greater benefit than water alone. Remember that food is also a key component of hydration, and snacks like melon and cucumber can contribute significantly to your daily fluid intake.

In severe cases of dehydration, especially with symptoms like dizziness, confusion, or lack of urine output, professional medical attention is required. IV fluids, administered by a doctor, are the fastest way to replenish fluids and electrolytes in life-threatening situations.

Conclusion

While plain water is an essential part of a healthy diet, it is not the most rapidly hydrating fluid under all circumstances. For quick and effective rehydration, especially when electrolytes are depleted due to illness or intense activity, oral rehydration solutions are superior. For longer-lasting hydration, especially following exercise, milk's combination of electrolytes, protein, and fat makes it a surprisingly effective choice. By understanding the science behind fluid absorption and the roles of electrolytes and nutrients, you can make informed decisions to optimize your hydration, whether you are simply thirsty or recovering from intense exertion or illness. A diet rich in water-dense foods also plays a significant role in maintaining proper fluid balance.

Frequently Asked Questions

Yes, in cases of moderate dehydration where electrolytes have been lost, an ORS is more hydrating than plain water. The combination of glucose and electrolytes in ORS enhances fluid absorption in the intestines, speeding up the rehydration process.

Milk is more hydrating over a few hours than water because it contains lactose (a sugar), protein, and fat. These components slow down the rate at which fluid is emptied from the stomach, which leads to less urine being produced and longer fluid retention.

The Beverage Hydration Index (BHI) is a measure used to assess how well different beverages hydrate the body. It compares the amount of urine produced after drinking a specific beverage versus drinking an equal amount of plain water.

Cucumber (over 95% water) and iceberg lettuce (over 95% water) are among the foods with the highest water content. Other highly hydrating foods include watermelon, tomatoes, celery, and spinach.

Sports drinks can be useful for hydration, especially during or after intense exercise lasting over an hour, as they contain electrolytes and carbohydrates. However, for most people and general hydration, water is the best choice due to its lack of added sugars and calories.

One of the best indicators of proper hydration is the color of your urine. When well-hydrated, your urine should be a pale yellow color, like lemonade. Dark yellow urine can indicate dehydration.

While caffeine is a mild diuretic, moderate consumption of coffee and tea does not lead to dehydration. The water content in these beverages typically outweighs the diuretic effect. However, excessive caffeine intake can cause increased urination.