Q: Sports drinks like Gatorade and Powerade are chock-full of electrolytes, which are believed to require replenishing after strenuous activity (or less seemly, a bout of gastrointestinal distress). What exactly is an electrolyte and why do we need to maintain a steady supply?

A: Electrolytes is a catch-all term for substances that assist in various biological and metabolic processes, such as chemical reactions and fluid balance. They get the name because of their positive or negative electrical charge when dissolved in water. Those charges contract muscles and control hydration levels.

Sodium, magnesium, potassium, calcium, chloride, phosphate and bicarbonate are all considered electrolytes. Too much or too little of any of them can result in adverse effects, such as weakness, muscle cramps or confusion.

Heavy activity that produces a lot of sweating can result in loss of electrolytes, though the effects of depletion usually occur an hour or more after the activity. Sports drinks might be suitable if you’ve been sweating heavily for a prolonged period of time, but they also often come packed with unnecessary sugar. Water almost always is the better option.