The Influence of Protein on Beverage Hydration Efficacy: A Systematic Review and Meta-analysis

Background Beverage composition can dictate effectiveness of hydration and rehydration by influencing several physiological processes, including gastric emptying rate, intestinal absorption and oncotic pressure. While the benefits of solutes such as carbohydrates and electrolytes are well established in hydration beverages, research into the efficacy of protein inclusion remains sparse. Objective The aim was to evaluate the effects of protein-containing beverages on hydration and rehydration, in terms of fluid retention, cumulative urine, net fluid balance (NFB) and plasma volume (PV) change, when compared with a control beverage. Methods The systematic review was pre-registered (Open Science Framework) and conducted in accordance with PRISMA guidelines. PubMed, Embase, the Cochrane Library and Web of Science were searched from inception to February 2026 for human trials (≥ 18 years) researching hydration or rehydration following hypohydration or euhydration. To be eligible, beverages contained ≥ 2 g/L protein and reported at least one hydration outcome. Random-effects meta-analyses was performed using standardised mean differences (SMD). Results Overall, 16 studies were included in this review (205 participants; 17.1% female, euhydrated: n = 2, hypohydrated: n = 14). Mean protein content in the studies was 23.7 ± 9.9 g/L. Meta-analysis performed on the rehydration studies revealed greater fluid retention (SMD 0.66, 95% CI 0.39–0.93, P < 0.00001, Z = 4.85, medium effect), reduced cumulative urine output (SMD − 0.71, 95% CI − 0.99 to − 0.43, P < 0.00001, Z = 4.93, medium effect), as well as increased NFB (SMD 0.58, 95% CI 0.30–0.85, P < 0.0001, Z = 4.10, medium effect) and augmented PV change (SMD 0.29, 95% CI 0.03–0.55, P = 0.03, Z = 2.19, small effect) following ingestion of protein. Conclusions Protein-containing beverages confer an advantage over a control beverage on hydration metrics. These findings support protein as a potentially beneficial addition to rehydration strategies, however, there was a lack of female participants (17.1%), as well as plant-based beverages, limiting the generalisability of findings to female athletes, as well as those with diets devoid of lactose products.