Home/Guides/Is milk more hydrating than water?
Milk doesn’t look like a hydration drink. It looks like food you drink: thick, caloric, closer to a snack than a thirst-quencher. The research says otherwise, cautiously. In a randomized trial that ranks beverages by how long they keep you hydrated, both skim and whole milk beat plain water. Modestly, and for reasons that have nothing to do with marketing.
Is milk actually more hydrating than water?
Yes, a little. In a 2016 trial known as the Beverage Hydration Index (BHI), researchers gave 72 healthy men a liter of one of 13 drinks and tracked how much of that fluid stayed in their bodies over the next four hours, scored against a plain-water baseline of 1.00. Skim milk came in at 1.58. Whole milk came in at 1.50. Both mean people held onto roughly half again as much fluid as they would from the same volume of water.
That’s a real effect. It’s also a small one, drawn from a single trial, not a lifetime of breakfast habits.
Why does milk retain fluid longer?
The BHI researchers point to three things slowing milk down on its way through you: protein, fat, and electrolytes (the sodium and potassium your body uses to hold onto fluid). Water empties from your stomach into your bloodstream fast, and just as fast out again through your kidneys. Milk’s protein and fat make your stomach empty more slowly, spreading that same liter over a longer window. Its electrolytes do the rest, sodium especially, signaling your kidneys to hang onto water rather than pass it straight through as urine.
Milk’s own sodium and potassium, not any special hydrating power, are most of why it outlasts water in your body.
It’s the same mechanism, not a coincidence, behind the trial’s other top scorer: oral rehydration solution (ORS), essentially water with electrolytes added on purpose.
What did the 2016 trial actually find?
The trial, run by Maughan and colleagues across three UK labs, is about as close as hydration science gets to a leaderboard. Seventy-two healthy men, tested after an overnight fast, each drank a liter of one of 13 beverages; researchers measured urine output for the next four hours and compared it back to the same men drinking plain water. Less urine relative to water means the drink held on to more of its fluid.
| Drink | Hydration vs water |
|---|---|
| Skim milk | 1.58 |
| Oral rehydration solution | 1.54 |
| Whole milk | 1.50 |
| Water | 1.00 (benchmark) |
Milk placed near the top of that list. So did ORS. Everyday drinks like tea, cola, and coffee (which we’ve covered before) landed statistically indistinguishable from water: not better, not worse.
How to count milk toward your hydration
Our honest answer: give milk credit, but not the full lab number.
The trial’s roughly 150% figure for whole milk describes one controlled lab morning, not a Tuesday where you’ve had cereal at breakfast and coffee at your desk. That’s part of why we built Brim to credit a glass of milk at 130% of water (Premium), a bit below what the lab data alone would suggest. A glass of milk also carries about 12 g of natural sugar riding along with that fluid, which the raw hydration number doesn’t account for. Cautious beats clever where the evidence is noisy.
You can look up milk, and every other drink Brim tracks, in the BHI Hydration Index Lookup, credit values and all.
What this evidence doesn’t prove
Keep the caveats in view. The trial studied 72 healthy men, not women, older adults, or anyone with a health condition. It measured four hours after a single liter, not a full day of ordinary eating and drinking. And it holds up even after adjusting for the fact that milk is itself mostly water (about 88%): the corrected numbers drop to roughly 1.44 for skim and 1.32 for whole milk, still ahead of water, just by less.
None of that makes milk a water substitute. It’s a modest, well-evidenced bonus on top of your water intake, not a reason to swap your glass for a carton.
Key takeaways
Milk modestly out-hydrates water. Skim milk (1.58) and whole milk (1.50) beat the 1.00 benchmark in a 2016 randomized trial.
Protein, fat and electrolytes slow gastric emptying, letting your body hold onto more fluid for longer.
The evidence is real but narrow: one trial, a few hours, 72 healthy men. Not a mandate to drop water for milk.
Brim credits milk at 130% (Premium), below the lab figure, because a glass also carries natural sugar.
Frequently asked
Does milk hydrate you better than water?
In a 2016 randomized trial (the Beverage Hydration Index), skim milk (1.58) and whole milk (1.50) both kept people hydrated longer than water at the 2-hour mark. The effect is real but modest, not a reason to swap out water.
Why is milk more hydrating than water?
Milk carries protein, fat and electrolytes (sodium and potassium) that slow how fast your stomach empties into your bloodstream. That slower release means more of the fluid stays with you instead of passing through quickly as urine.
Should I drink milk instead of water?
No. The trial measured a few hours in a lab, not a full day of normal life, and milk brings calories and sugar that water doesn’t. Treat it as a mild bonus on top of water, not a replacement.
Does skim milk hydrate better than whole milk?
Slightly. Skim milk scored 1.58 versus whole milk’s 1.50 in the 2016 trial, likely because it carries less fat slowing digestion and more water by volume.
How does Brim count milk toward hydration?
Brim credits a glass of milk at 130% of water (Premium), a bit below the roughly 150% lab figure, because a glass also carries about 12 g of natural sugar.
