But when the fat cell starts to get dehydrated, things change: The cell begins making and storing more fat, and it becomes less able to burn fat for energy. Instead of using fatty acids as fuel, it holds onto them.
To make even more fat, the cell increases a special channel (called aquaporin 9) that pulls in extra glycerol, which is the backbone of triglycerides, a storage form of fat Meanwhile, insulin pushes more glucose (sugar) into the cell, which also gets turned into fat.
So, given that the many studies listed above used plain water as the hydration source, is it the best beverage for optimal hydration?
While water is foundational, SO important, and widely accessible, there are other beverages that also may be helpful in retaining fluids—especially in physically demanding or high-heat conditions. Let’s explore how hydration status is measured and how other drinks stack up against water.
How is “hydration” status measured in research studies?
Hydration is measured in a variety of ways, including:
Blood markers such as serum osmolality and sodium concentration assess fluid balance and solute concentration in the bloodstream.
Urine markers like urine specific gravity and osmolality indicate how concentrated the urine is, helping to detect dehydration.
Body weight changes over short periods (e.g., before and after exercise) reveal acute fluid loss; advanced methods like bioelectrical impedance analysis (BIA) and salivary osmolality provide additional hydration insights in clinical or research settings. BIA estimates total body water (TBW) and fluid compartments (intracellular vs. extracellular).
Then there is the Beverage Hydration Index (BHI). The BHI measures how effectively a specific drink is retained in the body compared to plain water, which has a BHI of 1.0. Beverages like oral rehydration solutions, milk, and electrolyte drinks often have higher BHI values—typically ranging from 1.2 to 1.6—indicating better hydration and fluid retention.
In a 3-week trial among Guatemalan sugarcane farmers laboring in extreme heat, researchers tested the effects of increasing electrolyte beverage intake on hydration, muscle damage, and kidney function. The intervention drink was a WHO-style oral rehydration solution (ORS) containing 2.6 g sodium chloride, 2 g potassium chloride, 13.5 g glucose, and 40 kcal per liter, provided at escalating doses: 2.5 L per day in Week 1, 5 L per day in Week 2, and 10 L per day in Week 3. Results showed that higher electrolyte intake was associated with lower levels of muscle breakdown (creatine kinase), stable kidney function, and better overall hydration, supporting the use of electrolyte-enhanced fluids to protect worker health in hot, physically demanding environments.
Additionally, a study on the Beverage Hydration Index ranked drinks for their level of hydration. In the study, seventy-two healthy, physically active men aged 18–35 participated in a randomized, controlled hydration study conducted across three university laboratories. After an overnight fast and standardized water intake, each participant consumed 1 liter of still water or a test beverage, and hydration status was assessed through cumulative urine output over several hours, serum and urine osmolality, and urinary sodium and potassium concentrations to calculate the Beverage Hydration Index (BHI) for each drink.
The findings showed that compared to plain water, oral rehydration solution (a version of electrolyte water with a small amount of glucose), orange juice, and milk were above-average hydration beverages.
Oral rehydration solutions seem to hydrate more effectively than plain water because they contain sodium (± other electrolytes) and small amount of glucose, which help pull water into cells via specialized transporters, restoring cellular fluid balance.