Electrolytes for runners: The Definitive Guide (2024)

Knowing what we know now about the latest research on hydration, dehydration, and performance, how should you structure your own hydration routine, and what’s the best way to figure out how much you need to drink?

Does Weighing Yourself Before and After a Run Measure Hydration Loss?

One of the most popular ways of measuring your water needs is by weighing yourself before and after you run, then calculating the difference.

It seems fairly basic: if you go out for a run in the heat, you sweat out a lot of water and need to replace it.

But, there’s more to it than that.In fact, scientific research has shown that there are a few problems with this model.

First, this doesn’t measure your electrolytelevels.

Second, not all of the weight you’re losing is water!

A significant portion is fuel—carbs and fat, burned for energy during the course of your run.

The exact caloric cost of running varies from person to person, but:

• A figure of 120 calories per mile is about right for most runners.
• So, for example, over the course of an eight or nine-mile run, you’d expect to burn about 1000 calories.
• If you are running at an easy pace, about half of these calories will come from carbs, and the other half will come from fat.
• After doing some math on the energy content of carbs and fat, you’ll find out that you’ll be losing almost half a pound of fuel during your run.
• On top of this, a wide body of research has established that your body stores water alongside glycogen, the molecule carbohydrates are converted into for storage.

In one representative study by Karl-Erik Olsson and Bengt Saltin at the Karolinska Institutet in Sweden, 19 healthy subjects had their total body water and muscle glycogen content measured before and after a three-day period during which they consumed only fat and protein, depleting their body’s carbohydrate stores.

Following this, the subjects ate a carb-rich diet again for four days and the measurements were taken again.

Olsson and Saltin demonstrated a fluctuation in body water content according to the concentration of glycogen stored in the muscles, to the tune of three to four grams of water per gram of carbohydrate.

For a runner,this means that each gram of carbohydrates that you burn liberates a few grams of waterwhich can help maintain your hydration level, even though you’re losing water to sweat.

What About Drinking to Thirst?

Timothy Noakes, a South African exercise physiologist and medical doctor, has demonstrated in several studies that athletes can lose at least 2.2 pounds of weight during exercise, and possibly up to 4.4 pounds, without any measurable decrease in hydration.

Additionally, Noakes points out that runners seem to have differing levels of sensitivity to water loss.

Some become extremely thirsty after only a pound or two of body weight lost, while others lose up to 8% of their body weight during a race, even when they’re drinking water en route!

Some multi-hour ultramarathon events feature weight checks at intermediate points along the course, but primarily to preventoverhydationin the form of hyponatremia, a dangerous condition that results from drinking too much water or sports drink.

What About Monitoring the Color of Your Urine?

Unfortunately, that too fails to pass scientific muster.

A 1999 study by three researchers at Maastricht University in the Netherlands compared the color and volume of urine production in eight trained cyclists before and after a long cycling session in the heat which led to a 3% loss in body weight.

While it is true that urine color and output followed the trends we’d expect—a small amount of dark yellow urine immediately after exercise, then increasingly clear urine and larger volumes produced as the subjects rehydrated—neither the color of the urine nor its volume were statistically correlated with the amount of water in the body.

In fact, the onlyscientifically valid measurement of hydration is the concentration of your blood plasma, which is not exactly easy to measure.

So, How Can We Accurately Measure Hydration and Electrolyte Loss?

So what’s a runner to do?

Well, luckily for you we’ve developed a calculation that factors in your carbohydrate and fat burned while also compensating for glycogen storage and actual sweat loss.

Or, if you want to do it yourself, here are the steps to take:

Step 1: Calculate your total calories burned. 120 calories per mile is about right for most runners.

Step 2: Calculate percentage of calories burned from fat and carbohydrates. This is a reflection of intensity. This is a relatively complicated calculation, but if you want the in-depth detailscheck out the article we did on this earlier here.

Step 3: This will give you how many grams of carbs and fat you burned.

Step 4: Measure how much actual weight you lost

Step 5: You can now subtract the value from how many grams of carbs and fats you burned from total weight loss. The difference is how much sweat you lost.