Beverages containing electrolytes, carbohydrates, and a food matrix result in greater fluid retention in the body over a four-hour period compared to plain water.

Study: A randomized trial modeling the effects of solutions with low to moderate glycerol and sodium concentrations on fluid balance in healthy, active adults.

Drinks with extra salts and a sugar-like substance kept more water in the body than plain water, just like the claim says. The more of these ingredients, the better the body held onto the fluid.

Study: Caffeinated Energy Drink Formulations Differentially Impact Hydration Versus Water: Does Habitual Caffeine Intake or Biological Sex Matter?

Drinks with sugar, salt, and caffeine kept fluid in the body just as well as water, but drinks with caffeine and salt but no sugar made people lose more fluid. So adding sugar and salt helps your body hold onto water better.

Study: Time-course changes in fluid balance following ingestion of a novel glycerol-electrolyte solution in a randomized trial.

This drink with salts and glycerol (a substance that helps hold water) made people keep more fluid in their bodies and pee less than when they drank plain water — especially in the first 4 hours.