Rare Sugar Allulose Outperforms Standard Sweeteners at Restoring Fluids After Exercise

For decades, the science of rehydration has rested on a simple premise: to replace the water lost in sweat, athletes should drink fluids that contain a modest amount of sugar alongside electrolytes. The sugar is not there merely for taste. Glucose actively drives water absorption in the gut through sodium-glucose cotransport, and it helps the body hold onto the fluid it takes in rather than promptly excreting it. The problem is that the caloric and glycemic cost of sugary sports drinks has become increasingly unattractive, particularly for recreational exercisers, people managing blood glucose, and anyone drinking fluids outside of intense training. A new randomized, double-blind, crossover trial published in Food Science and Biotechnology suggests that a little-known rare sugar called allulose may solve this dilemma, delivering the fluid-retaining benefits of a transportable carbohydrate with almost none of the caloric burden.

Allulose, sometimes labeled D-allulose or D-psicose, is a rare sugar that occurs naturally in small quantities in foods such as figs, raisins, and jackfruit. Chemically, it is a C-3 epimer of fructose, meaning it shares fructose’s molecular formula but differs in the spatial orientation of a single hydroxyl group. That tiny structural difference has large metabolic consequences: allulose is poorly digested in the small intestine, contributes negligible calories, and does not meaningfully raise blood glucose or insulin. It has attracted growing attention as a bulk sweetener for sugar-reduced beverages and foods, and recent work has explored how gut microbes can even utilize it as a substrate. Yet while its glycemic profile is well documented, rigorous human evidence that allulose can actively improve rehydration, rather than simply avoid harming it, has been scarce.

The new study, led by Hye Rim Kim and Jinsoo Noh of Samyang Corporation together with colleagues at Yonsei University in South Korea, set out to fill that gap with a carefully controlled human trial. Fifteen healthy men completed the protocol, which used a randomized, double-blind, crossover design widely regarded as the gold standard for nutrition interventions. In a crossover trial, each participant serves as his own control, experiencing both experimental conditions in randomly assigned order with a washout period in between. This design minimizes the noise created by individual differences in sweat rate, fitness, and baseline hydration, which are substantial in fluid-balance research. Neither the participants nor the investigators knew which beverage was consumed on a given trial day, protecting the results from expectation effects.

The experimental challenge was deliberately physiological. Each participant first underwent exercise-induced dehydration, losing body water through physical exertion in a controlled setting, before consuming one of two electrolyte-matched beverages. The drinks were identical in their electrolyte content, so the only meaningful variable was the sweetener: one contained allulose, while the control beverage was sweetened with sucralose, a non-nutritive sweetener that provides sweetness without any carbohydrate transport activity. By matching electrolytes and holding volume constant, the researchers isolated the specific contribution of allulose to the rehydration process. The team then tracked an extensive panel of outcomes, including plasma volume recovery, fluid retention, thirst ratings, body water composition measured by bioelectrical impedance analysis, urine specific gravity, blood glucose, and body temperature.

The headline result was striking. Plasma volume, the liquid component of blood that supports cardiovascular function and thermoregulation during exercise, recovered far more completely in the allulose condition. Participants who drank the allulose beverage showed a plasma volume recovery of roughly 28 percent relative to their post-exercise deficit, compared with only about 4 percent after the sucralose drink, a difference the authors report as statistically significant at p = 0.0001. Fluid retention told a similar story: the allulose drink allowed the body to hold onto approximately 91.5 percent of the ingested fluid, whereas the sucralose control retained about 80.6 percent, a gap of more than ten percentage points that reached significance at p = 0.0023. In practical terms, the allulose beverage did not just quench thirst; it kept the water inside the body where it could do physiological work.

Subjective thirst followed the objective measurements. Participants reported a significantly greater reduction in thirst after the allulose beverage, with a mean thirst reduction score of 6.47 compared with 4.60 for the control, significant at p = 0.0012. This matters because thirst is a surprisingly poor guide to true rehydration. People often stop drinking once oral sensations fade, long before plasma volume and cellular hydration are fully restored, a phenomenon that contributes to chronic mild dehydration in athletes and ordinary people alike. A beverage that both relieves thirst and measurably improves fluid retention addresses both the behavioral and the physiological sides of the problem. Notably, the researchers found no glycemic cost: blood glucose was not adversely affected, and there was no thermoregulatory penalty, meaning the sugar did not interfere with the body’s temperature control after exercise.

Why would a poorly digested sugar enhance fluid retention at all? The most plausible mechanism, which the authors situate within existing literature, involves sodium-glucose cotransport. The intestinal transporter SGLT1 couples the uptake of glucose and sodium, and in doing so creates an osmotic gradient that pulls water across the gut lining. Research on this transporter has shown it is an extraordinarily efficient facilitator of passive water movement, which is precisely why oral rehydration solutions for illness rely on glucose and sodium in balanced proportions. Although allulose is only partially absorbed, some transport activity appears sufficient to augment water uptake and, critically, to help retain absorbed fluid within the vascular and cellular compartments rather than letting the kidneys excrete it rapidly. The kidney’s own sodium-glucose cotransport systems may also contribute to keeping filtered water in the body.

The study’s measurement strategy adds credibility to these conclusions. Bioelectrical impedance analysis allowed the team to distinguish total body water, extracellular water, and intracellular water, offering a window into where the retained fluid actually resided. Urine specific gravity served as a standard clinical index of hydration status, reflecting how concentrated the kidneys are making urine; a lower value after rehydration indicates the body is conserving water rather than dumping it. Combining these objective markers with plasma volume estimates and subjective thirst scales gives a more complete picture than any single measure could, and the consistency across outcomes strengthens the case that the effect is real rather than a statistical artifact.

Several caveats deserve attention. The sample comprised fifteen healthy men, so the findings cannot yet be generalized to women, older adults, or clinical populations, and the modest sample size, while typical for crossover metabolic studies, means the confidence intervals around the effect estimates are wide. The trial was funded by Samyang Corporation, which provided the study material, and most of the authors are affiliated with the company; the disclosure is transparent, but independent replication will be important before the results are treated as settled. The comparison sweetener, sucralose, was a sensible inert control, but future work comparing allulose directly against glucose-based sports drinks would clarify whether it matches or exceeds the gold standard, not merely whether it beats a non-transported sweetener. Doses, timing, and effects during exercise rather than after it also remain open questions.

Even with those limitations, the implications are compelling. Sports nutrition guidelines have long emphasized that fluid replacement after exercise should account for electrolyte losses and that carbohydrate can aid absorption, but the caloric arithmetic has always been awkward for the vast majority of people who exercise for health rather than performance. Sugar-sweetened beverages are firmly implicated in the global rise of obesity and type 2 diabetes, while purely non-nutritive sweeteners have faced persistent questions about metabolic effects. Allulose occupies a genuinely different position: it tastes and behaves like a sugar in formulation, it is metabolically stable and largely excreted or fermented rather than converted to energy, and this trial now provides human evidence that it can actively enhance plasma volume recovery and fluid retention after dehydration. If larger independent trials confirm these findings, the rehydration aisle could be reshaped by a rare sugar that most consumers have never heard of, one that helps the body hold onto water without holding onto calories.

Subject of Research: Effects of allulose on post-exercise rehydration and plasma volume recovery in humans

Article Title: Allulose enhances plasma volume recovery and fluid retention after exercise-induced dehydration: a randomized, double-blind, crossover trial

Article References: Allulose enhances plasma volume recovery and fluid retention after exercise-induced dehydration: a randomized, double-blind, crossover trial. (n.d.). https://doi.org/10.1007/s10068-026-02329-z

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02329-z

Keywords: allulose, rehydration, dehydration, plasma volume, fluid retention, exercise, rare sugar, sports nutrition, sucralose, crossover trial, sodium-glucose cotransport, low-calorie sweetener