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Given how often we see the word “electrolyte” listed on sports nutrition products, you’d think we’d know a little more about them. Instead, many of us drink, chew, and slurp down pricey products that claim to restore electrolytes and prevent fatigue without giving the ingredient list another thought.

The truth isn’t quite that simple. Here’s everything you need to know about electrolytes—and how to best tailor the products that contain them to your body’s needs.

What Are Electrolytes?

“Electrolytes are the medium through which electricity gets transferred throughout the body,” says Stavros Kavouras, director of the Hydration Science Lab at University of Arkansas. enter our bodies through food or drink, then turn into the charges that spark cell function, making them responsible for just about everything. They play a role in muscle contraction, metabolism, and various other cell functions, says Robert W. Kenefick, a physiologist with the U.S. Army Research Institute of Environmental Medicine who specializes in hydration. Without electrolytes, our cells would have trouble self-regulating, which would throw many of our basic bodily functions totally out of sync. According to Kenefick, when we talk about what we may lose through sweat—remember, electrolytes are salts, after all—we’re referring to sodium, chloride, and potassium, and small amounts of calcium and magnesium.

What Causes an Electrolyte Imbalance?

“For the most part, if you have a normal diet, particularly a diet in the U.S., you’re probably getting all the electrolytes you need on a daily basis,” Kenefick says. Electrolytes are lost naturally through urination and sweat and then replaced through meals.

Sweat actually contains a relatively low concentration of electrolytes, which varies widely based on the individual. “From person to person, the difference in electrolytes lost through sweat can vary by as much as two to three times,” Kavouras says. Some people are genetically heavy sweaters, while others are low sweaters. Some are called salty sweaters, meaning they have very high sodium concentrations in their sweat. (You know you’re a salty sweater if you get white streaks or rings on your clothing when you work out, Kavouras says.) Some people are a heavy and salty sweater combo, which means they have to pay closer attention to the amount of electrolytes they take in. But for the average athlete, the length and intensity of exercise are the biggest factors that determine when you need to supplement.

When Should You Reach for Electrolytes?

“Unless you exercise for more than three hours, you don’t need to add electrolytes,” Kavouras says. “No one has complications related to electrolyte imbalance for anything, assuming you start your exercise in a balanced state.”

Anything longer than that, though, and you’re at risk for depletion. “Individuals who are doing work where they would be sweating profusely for a number of hours, particularly day after day, need to take electrolytes into account,” Kenefick says. That includes endurance athletes, some military personnel, certain manual occupations, and sports that take place in the heat and require multiple practices a day.

That said, longer doesn’t always translate to needing more of the salty stuff. Say you go on a gentle six-hour hike on a mild autumn morning. You probably aren’t sweating very much and, therefore, likely don’t need additional electrolytes. But if you’re doing a 50-mile bike ride at high noon in August, which would be a shorter duration, you’d be wise to stash some electrolyte products in your singlet.

How Do Electrolytes Help?

Chances are you’ve experienced severe muscle cramps at some point in your life. You likely assumed the cramps happened because you were low on electrolytes. But science hasn’t been able to back that up despite the role of electrolytes in muscle contraction, Kenefick says. In , traveling at faster speeds was actually more likely to be a predictor of cramping than dehydration or decreased electrolyte levels. “You’d be more inclined to be fatigued because you’re running low on glucose—which feeds energy into your muscles—than because of an electrolyte imbalance,” Kenefick says.

It’s still possible that electrolytes, particularly sodium, can aid performance. When researchers had one group of athletes consume salt capsules in addition to sports drinks during a half Ironman and had a control group consume only sports drinks, the group supplementing with sodium completed the race an average of 26 minutes faster, according to a study in the . The group drinking just the sports drinks replaced around 20 percent of the sodium they lost during the race, while the group adding salt tabs replaced around 71 percent of the sodium they lost through sweat. Sodium supports your heart by keeping the blood vessels around it filled with the right amount of water. That allows it to maintain blood flow to the muscles in need during effort, which could have a beneficial effect on performance, Kavouras says.

Where Should Your Electrolytes Come From?

The truth is that the parameters surrounding proper electrolyte consumption remain vague and largely undeveloped. As far as scientists know, there’s no single method that’s best. Sports drinks win on convenience, Kavouras says. You get hydration, carbohydrates, and electrolytes all in one easy-to-consume bottle.

Unless you’re in the middle of an intense endurance effort—like, say, a marathon—you can get what you need without any supplementing. “I recommend people eat real food, because some manufactured foods are super-concentrated,” Kenefick says. “When you’re taking in this bolus of salt and glucose, it can sit in your stomach and exacerbate GI distress.”

“Just don’t do what I once saw someone doing at an ultra—dumping half a salt shaker in his mouth at a checkpoint,” Kavouras says. “You don’t need that much!”