Can Drinking Milk Help You Stay Hydrated?

You’ve probably heard the standard advice: drink eight glasses of water a day and you’ll be fine. But what about the milk in your cereal bowl or the latte you sip mid-morning? If you’re counting fluids, milk seems like it should count — but a lot of people wonder whether the protein, fat, and sugar somehow cancel out the water content.

The short answer is that milk does count as a hydrating beverage, and in some situations it may even keep you hydrated longer than plain water. The catch is that context matters: the same qualities that make milk a powerful hydrator after a workout also add calories and protein that most people don’t need during a regular day at a desk.

How The Beverage Hydration Index Measures Milk

Researchers use a scale called the Beverage Hydration Index (BHI) to compare how different drinks affect fluid balance. Water is set as the reference at 1.0, and anything above that keeps you hydrated for a longer period after drinking.

A 2022 study found that both whole milk and skim milk scored higher on the BHI than plain water. In practical terms, that means milk held onto more fluid in the body over the two-hour window after the participants drank it.

What The Numbers Actually Mean

A BHI above 1.0 doesn’t mean milk is “better” in every scenario. It simply means the body retains more of what you drank, which is useful when you’re dehydrated from exercise but less relevant when you’re just going about your day with a glass of water nearby.

Why Milk Stays In Your System Longer

Milk’s ability to linger in the body comes down to two main factors — its electrolyte content and its nutrient density. Both slow down how quickly the fluid moves through your system.

• Electrolytes like sodium and potassium: These minerals help the body hold onto fluid instead of excreting it quickly. Plain water lacks significant electrolytes, so more of it passes through as urine.
• Energy density from protein, fat, and carbs: The calories in milk slow gastric emptying — in other words, the stomach releases milk into the small intestine more gradually than water, which extends the rehydration process.
• Natural carbohydrate content (lactose): Lactose aids in fluid absorption through the gut, similar to how sports drinks use sugar to pull water into the bloodstream.
• Protein content: Both casein and whey proteins contribute to a slower digestion rate, which further delays fluid loss.

Researchers who study rehydration point to this natural combination of electrolytes, protein, and carbs as the reason milk can outperform water in post-exercise scenarios. It’s essentially delivering nutrients while also replenishing fluids.

Comparing Milk To Other Hydration Options

The 2022 study didn’t just test milk against water — it also compared it to sports drinks and oral rehydration solutions. Milk matched the fluid-retention performance of medical-grade rehydration drinks and beat the standard sports beverage.

Milk’s main trade-off is its calorie load. An 8-ounce glass of whole milk carries roughly 150 calories, which is about three times what a typical sports drink delivers. For an athlete needing both fluid and fuel after a long run, that’s fine. For someone who just wants a glass of water with lunch, the extra calories aren’t needed.

When Milk Makes Sense For Hydration

There are specific situations where replacing water with milk can improve hydration outcomes. The context matters more than the beverage itself.

1. After intense or prolonged exercise: When you’ve sweated out significant fluid and electrolytes, milk’s sodium and potassium help restore balance while also providing protein for muscle repair.
2. When you’re having trouble keeping fluids down: Milk’s thicker consistency and nutrient density can be easier to tolerate than plain water for some people recovering from mild illness.
3. For children who resist plain water: Given that milk is about 87% water, it can be a practical way to keep a child’s total fluid intake up without pushing water they won’t drink.
4. During hot weather if you’re eating a meal anyway: Milk at breakfast or lunch contributes to overall daily fluid needs without requiring a separate hydration effort.

Keep in mind that for everyday casual sipping, water remains the standard. Verywell Health makes the point that plain water is the water best everyday hydration choice because it’s calorie-free, sugar-free, and always available. Milk is a hydrating supplement, not a replacement.

What The Research Shows About Milk And Fluid Retention

The strongest evidence for milk as a hydrator comes from the BHI studies themselves. A 2016 randomized trial published in the American Journal of Clinical Nutrition tested milk, sports drinks, water, and several other beverages across multiple participants. Milk consistently came out ahead in fluid retention.

A 2022 follow-up study confirmed the same pattern, including the finding that milk and oral rehydration solutions behaved almost identically in terms of keeping fluid inside the body. That has practical implications for athletes who dislike the taste of sugary sports drinks or want a more natural option post-workout.

What The Mechanism Looks Like

Harvard Health’s review of the milk fluid retention study explains that the combination of electrolytes, protein, and carbohydrates in milk is what slows down the rate at which the body releases fluid. Sodium, specifically, encourages the kidneys to hold onto water rather than excreting it quickly. That’s the same reason oral rehydration solutions contain salt — and milk happens to contain it naturally.

The overall picture is that milk is a functional beverage — it hydrates and nourishes at the same time. That’s useful in the right context, but it’s also why it shouldn’t replace water for general daily hydration.

The Bottom Line

Yes, milk can help you stay hydrated — and in some head-to-head comparisons, it outperforms water at keeping fluid in your body after exercise. Its natural electrolytes and energy density give it a bump on the Beverage Hydration Index. But for most people on most days, water remains the simplest, lowest-calorie, and most practical option. Milk works best as a post-workout recovery drink or as part of a meal where hydration and nutrition overlap.

If you’re managing specific health conditions like kidney disease or heart failure that require careful fluid and electrolyte tracking, check with your doctor or a registered dietitian before shifting away from plain water as your primary hydration source.