Prev NEXT 7Drink Plenty of Fluids When you exercise heavily, you lose electrolytes in your sweat, particularly sodium and potassium. © George Doyle/Getty Images Sweating means you're losing fluid. It's important to drink to replace fluids lost in sweat. Water is usually the best choice. If you are exercising for a long time, you may want the extra fuel from a drink that contains carbohydrate.