Wait a Minute, Is Milk More Hydrating Than Water? Here's the Best Time to Swap Water for Milk
Want to stay hydrated, but not a fan of sipping plain water all day? You're not the only one. Getting the generally recommended eight(ish) glasses of water a day can feel like a chore, but ordinary H2O isn't your only option. Other hydrating fluids and water-dense foods can help satisfy your thirst and help your body reach its daily water requirements, all the while offering some tasty variety.
While you can't totally replace water with another beverage, you can absolutely mix it up and benefit from the water content from other sources throughout the day. And there's one drink you might be surprised to learn is quite hydrating—and you probably have some in the fridge right now: milk.
That's right, this coffee addition and cereal accompaniment is not only known for its nutritional value, but also its hydrating properties. In fact, there's some scientific evidence that suggests milk is even more hydrating than water alone. Here, we dive into the existing research to find out whether milk beats out water in the hydration department, which type of milk (cow's or plant-based?) is the most hydrating, and what experts have to say.
Yes, Milk Is Hydrating, According to Research
The rumors are true: Milk is a great source of hydration. A March 2016 trial in The American Journal of Clinical Nutrition compared the effects of a variety of drinks—skim milk, whole milk, cola, diet cola, hot tea, iced tea, coffee, lager, orange juice, sparkling water, and a sports drink—on participants' fluid balances and then compared the results to still water. The findings indicated that both skim milk and whole milk are more hydrating than plain water, since when the participants drank milk they were able to retain fluids for longer periods of time than when they drank water.
Later studies have found comparable results. For instance, a May 2020 study in Nutrients found milk-containing beverages superior to water in their abilities to sustain fluids after ingestion. In fact, milk was found to have significantly higher effects on bodily hydration than water.
In both studies, researchers found that milk is associated with a lower urine output (peeing less frequently and therefore experiencing less fluid loss) compared to water. There's nothing wrong with peeing—and you should be visiting the restroom several times throughout the day to do so; however, emptying your bladder immediately after ingesting liquids isn't always best. Drinking milk and not having to go immediately after is an indicator that its hydrating effects last longer.
"Milk is about 90 percent water, meaning it can be a good source of hydration, especially in the summer months where people are more at risk for dehydration," confirms clinical dietitian Patricia Kolesa, R.D. "It also contains [the essential minerals] sodium and potassium, the electrolytes needed to replace what we sweat."
What Makes Milk So Hydrating?
Milk contains key nutrients, including electrolytes.
There are a few reasons why milk is so hydrating, the first being simply that it's not water. OK, that sounds totally backward, but here's why that's important: Plain water doesn't contain any calories or many nutrients. It can be a very small source of a few minerals, but that depends on the type of water. In comparison, milk is high in water and full of hydration-boosting nutrients. It's higher in calories and offers a balance of carbohydrates, fat, protein, vitamins, and minerals. When you drink such a nutrient-rich beverage, the body naturally takes longer to process it—the longer the body takes to absorb and process fluids, the longer it retains them.
The research also points to the electrolytes in milk. "Milk can actually be a very hydrating beverage option, more so than just plain water, thanks to its electrolyte content," confirms registered dietitian nutritionist Sarah Schlichter, MPH, RDN. "Milk can offer varying amounts of sodium, potassium, and calcium, which can help the body absorb water more efficiently, leading to better hydration levels."
The importance of electrolytes in hydration is nothing new. Electrolytes are essential minerals responsible for regulating the balance of fluids in the body. They don't add hydration themselves, but they help your body maximize the efficiency of your fluids so you're properly hydrated and for longer. The electrolytes in milk are especially helpful after an intense workout. When you sweat, you lose electrolytes, so drinking milk is a good way to replenish what you've lost.
Are Non-Dairy, Plant-Based Milks as Hydrating?
People avoid cow's milk for a variety of reasons: a vegan lifestyle, allergies, intolerance, personal taste preference, and the list goes on. Some of the most popular plant-based milks include almond milk, soy milk, and oat milk. Each option has long been compared to milk, and all have their pros and cons (read this handy non-dairy milk explainer for more).
But do non-dairy options like almond milk or oat milk boast the same hydrating power as cow milk? The answer is yes, to some degree.
Non-dairy alternatives have a high water content, but don't always offer as many replenishing nutrients.
Generally, "non-dairy milk alternatives also tend to contain higher percentages of water," says registered dietitian Tia Glover, R.D., which in some ways gives plant-based milk the upper hand in terms of hydration. For example, soy milk contains about 92 percent water, oat milk about 91 percent, and almond milk about 97 percent." This is in comparison to non-fat (skim) cow's milk, which contains about 90 percent water, and whole cow's milk, which contains about 87 percent water.
However, as mentioned, water content isn't the only indication of how hydrating something is—its nutritional makeup is also important. Milk is a great source of hydration-promoting electrolytes, carbohydrates, protein, and fat. Plant-based milks can certainly contain these nutrients as well, but in order to achieve comparable hydration results, you have to do your due diligence to choose a non-dairy substitute that's fortified with the same nutritional properties as cow's milk.
"All milks are in the same ballpark when it comes to supplying fluid," says registered dietitian Samantha Cassetty, R.D., M.S. "For instance, [a serving of] almond milk provides about 8 ounces of water—the same [amount] as 1 percent milk. However, since almond milk lacks the protein and carbohydrates found in milk, it may not help you retain fluid to the same degree, though it still contributes to your overall hydration status." Cassetty also adds that many milk swaps can be sneaky sources of added sugar, so read your labels carefully and try your best to stay within (or under!) the American Heart Association's recommended sugar limits (around 36 grams for men and 25 grams for women).
The potential hydrating effects of plant-based milk haven't been studied to the extent that cow's milk has. We know non-dairy milk is mostly made up of water (and definitely contributes to daily hydration), but we don't yet know if it's as effective for helping your body absorb, distribute, and retain water as cow's milk is.
When Should You Hydrate With Milk Instead of Water?
Armed with all of this knowledge, you might be wondering if it's best to drink milk instead of water from now on to stay hydrated—or at least wondering if there's a time when milk is the better option. The best time to choose a glass of milk over a glass of water would probably be after sweaty, vigorous exercise, when you likely need to replace the calories, electrolytes, and macronutrients (protein, fat, carbs) found in milk that water lacks.
"Milk can be a better option for people recovering from an intensive exercise regimen," says Luis Casaubon, M.D., ECNU, an endocrinologist and expert on diabetes. "It's great to drink after a workout because it contains protein and carbohydrates. Milk can also help reduce muscle soreness after an intense workout."
The Bottom Line:
Overall, however, water is still hydrator Number One.
"Milk is good for hydration, but water is a better option purely for hydration," Dr. Casaubon says, adding that water is typically the smarter option for those with diabetes, or whose doctor has prescribed a lower caloric intake, since milk can be high in calories and carbohydrates.
Ultimately, milk is an effective hydrator—it's great to know the milk you add to your cereal, splash in your coffee, or sip on its own contributes to healthy, daily hydration. But milk can't replace water altogether. If you're going to replenish with milk instead of water, go for it after a big workout or long day of hiking. Otherwise, water can't be beat!