The standing belief in sports nutrition is that a sports drink rehydrates you better than water, because the carbohydrate slows gastric emptying and the sodium helps hold serum osmolality up. A group at Nottingham Trent University noticed that most of the studies supporting this compared equal volumes of drink rather than equal volumes of water, and set out to see what happens when you correct for that.

The point is arithmetic. A 500 mL sports drink at six percent carbohydrate contains at least 30 mL less water than 500 mL of plain water. Every trial matched on total volume therefore gave the water arm extra water, which drives extra urine output, which makes water look worse at retention than it is.

Seventeen healthy adults, 15 men and 2 women, mean age 28, mean BMI 23.8, completed three trials in randomized crossover order at least seven days apart. Data collection ran from November 2024 to May 2025 in the UK.

Each trial began with cycling in an environmental chamber at roughly 35 degrees and 50 percent humidity, in ten minute blocks, until body mass fell about two percent. The achieved loss was consistent across arms at 1.90 to 1.92 percent, roughly 1.4 kg. Participants then rehydrated over one hour with a water volume equal to 150 percent of the mass they had lost, and sat for four more hours. All urine over the five hour window was collected, and capillary blood glucose was sampled seven times over the first two hours.

The three drinks were Raw Hydrate, a cold pressed juice of watermelon, pomegranate and lime; Lucozade Sport; and Highland Spring water.

The correction is the methodological contribution. Rather than pouring equal volumes, the investigators applied a weight correction for macronutrient content so that each arm delivered the same water. It worked: water volume came out at 2148, 2119 and 2125 mL across the three arms, with no difference between them. Total beverage weight did differ, as it has to, with the juice and sports drink arms both heavier than water.

On every rehydration measure, the three drinks were statistically indistinguishable. Water retention ordered itself in the expected direction, juice highest and plain water lowest, and did not reach significance at P = 0.059. Whether a larger sample would separate them is exactly the question the study cannot answer; it was powered a priori for 17 participants on a medium effect size for net water balance.

Blood glucose was the one place the drinks clearly parted. All three differed from each other, with the sports drink producing the highest two hour area under the curve, the juice intermediate, and water lowest. That result is unsurprising given the carbohydrate content but is the finding with the most practical reach, since it is the same for anyone drinking these products who is not dehydrated at all.

The dropout pattern is part of the result. Twenty nine people were recruited and twelve did not finish. Three of those withdrew with diarrhea after the fruit juice, which the authors report in the abstract rather than burying. The juice arm required an average of about 2,300 mL consumed inside an hour. That is a design artifact of rehydration research rather than a claim about the product, and the authors say so and recommend spreading intake over longer periods in future work. It still means the tolerability question is open in a way the headline result is not.

The funding is close to the product. The study was supported by an Innovate UK Knowledge Transfer Partnership between the University of Leicester and Innate-Essence Limited, which makes Raw Hydrate and supplied it. Innate-Essence co-funded the partnership. The first author is employed on that partnership and the second is on a PhD studentship awarded by the company. The paper states that Innate-Essence had no involvement in data collection, analysis or interpretation, and the disclosure is full and unusually specific. Separately, the senior author has received research funding from PepsiCo, and the first author has had conference fees covered by Danone Nutricia and taken prize money from the Gatorade Sports Science Institute. Worth noting that the finding is a null one for the sponsor's product against water, which is not the result a sponsor buys.

Registration was retrospective. The trial was registered on ClinicalTrials.gov as NCT07468539 after the fact. Ethics approval predates data collection.

The balance equations ignore ongoing losses. The formulas for net water balance and retention do not account for sweat or insensible loss during the five hour period, so both figures are probably slight overestimates. Because this is a crossover with matched laboratory conditions, the bias should fall on all three arms equally.

Fifteen of seventeen participants were men, all healthy, all screened to exclude kidney disease, liver disease, diabetes and regular medication. Nothing here extends to anyone with impaired concentrating ability.

Two things in this paper are worth pulling out for readers who have followed the kidney facts.

The first is the retention figure itself. Across all three arms, somewhere between 58 and 65 percent of the water consumed was in the toilet within five hours. Participants drank 150 percent of what they had lost and ended the window still short. This is the same physiology behind the eight glasses a day question and the reason thirst is a better guide than a target: a healthy kidney responds to a water load by suppressing vasopressin and clearing the excess quickly, and it does that whether the water arrives plain, sweetened, or cold pressed. Drinking more does not mean retaining more.

The second is the electrolyte content, which is lower than the framing suggests. Converting the salt figures, the sports drink supplied roughly 20 mmol of sodium per liter and the juice roughly 7. Both sit far below plasma. Sodium is the reason a rehydration solution holds water, which is why oral rehydration salts run at 60 to 75 mmol per liter and why none of these three drinks is one. Sodium is also the measure of dilution rather than salt content, the point of the hyponatremia entry, and it is the variable that would have had to differ for the arms to separate.

The juice does deliver potassium, and more than a casual reader would guess. At 135 mg per 100 mL across roughly 2,150 mL, the fruit juice arm carried about 2.9 grams, near 74 mmol, inside an hour. In a healthy adult with normal kidneys that is handled without incident and is a point in the drink's favor for blood pressure. In anyone with reduced excretory capacity it is a meaningful load, and it is the one number in this paper with a clinical edge the paper has no reason to discuss.