Do you need sugar to hydrate? Electrolyte absorption explained

As a coach, I fuel my low-carb clients (and myself) with mostly protein and fat. I’m a big believer in only using sugar when you really need it. However, lots of rehydration solutions — including the hydration strategy sanctioned by the World Health Organization — intentionally include glucose in the formula.

While I may not want the blood sugar bump, insulin spike, or empty calories, it’s true: Glucose can aid with hydration. In situations of extreme dehydration, for instance, glucose becomes a meaningful ingredient to help shuttle salt and water through your gut and into your bloodstream. As a result, many hydration brands include glucose as the “secret sauce,” implying that you need it for everyday hydration purposes.

Well, do you? Like many aspects of human physiology, the answer is context-dependent. Yes, glucose can help with rehydration during illness (like with cholera or diarrhea). And for reasons outside of hydration, sugar could provide extra fuel for endurance athletes during extended efforts. But most folks don’t need glucose for everyday hydration, and not everyone wants it in their drink. You shouldn’t have to limit your electrolytes based on the sugar content of a beverage — that’s why we don’t include glucose in LMNT.

Stick around for the next five minutes. I’ll unpack this sugar-hydration topic and offer practical tips on when to use glucose, fluids, and electrolytes for your hydration needs.

Hydration Basics 

When I talk about hydration, I’m talking about fluid balance. Proper fluid balance keeps your blood flowing, your skin moist, and your brain floating peacefully in your skull. 

Fluid balance depends on your intake of fluids AND electrolytes. For instance, getting enough sodium maintains blood volume, brain operation, and many other functions related to the distribution of water throughout your body.

The goal of healthy hydration is to consume and absorb a “Goldilocks” amount of fluids and electrolytes. This keeps your body running smoothly. Now, let’s see where sugar comes in.

How Does Glucose Help With Hydration?

Meet Dr. Robert Crane, the father of glucose-based rehydration. In the 1960s, Crane posited that glucose helps shuttle water and sodium through the gut and into the bloodstream.

His “cotransport hypothesis” was later verified with the discovery of a protein in the small intestine, named sodium-glucose cotransporter 1 (SGLT-1). SGLT-1 does what Crane imagined: When glucose is present alongside fluids and salt, the protein boosts the absorption of all three.

It’s important to mention, by the way, that glucose is just one type of sugar. Other sugars like fructose do NOT help with hydration. We’ll explore when it makes sense to utilize glucose shortly. First, though, let’s unpack why you don’t need glucose to hydrate.

Other Ways To Absorb Fluids and Electrolytes

There are, by and large, two reasons that glucose isn’t necessary for everyday hydration. First, sodium and fluids don’t require cotransporters to be absorbed. They can diffuse passively through the gut.

Second, glucose isn’t the only cotransporter in town. The following molecules also carry electrolytes through the gut and into the blood:

• Potassium and chloride. The Na-K-2Cl transporter transports sodium, chloride, and potassium into circulation.
• Phosphorous. The sodium-phosphate cotransporter does too. 
• Butyrate. This short-chain fatty acid (produced by gut bacteria) also boosts fluid and sodium absorption.
• Amino acids. The building blocks of protein help you absorb more electrolytes. 

Finally, clinical evidence suggests drinking super salty water (no sugar included) rehydrates ultra-endurance athletes with low sodium levels just as well as IV saline! If you needed glucose to rehydrate, you wouldn’t see that result.

Can Other Sugars Dehydrate You?

As you’ll recall, glucose enhances fluid and sodium absorption through the gut. So no, it’s not dehydrating. But glucose isn’t the only sugar in the modern diet. Sucrose (table sugar) and high fructose corn syrup (in sugary beverages, packaged food, etc.) contain glucose AND fructose. 

Fructose is no friend to healthy hydration. In one study, dehydrated rats became even more dehydrated after consuming an 11% fructose-glucose solution formulated to mimic a typical soft drink. The fructose rats had higher levels of a protein called copeptin (a precursor to antidiuretic hormone, which we produce in an effort to retain fluids) and higher blood sodium levels (hypernatremia). Both copeptin and hypernatremia are signs of dehydration. They also showed signs of kidney damage. Conversely, rats who drank stevia-sweetened water became less dehydrated despite drinking less fluid overall.

The possibility of dehydration is one of many reasons to avoid soft drinks, so-called “fruit juice,” and other sugar-sweetened beverages. High sugar intakes are also linked to heart disease, diabetes, cognitive decline, and many other conditions rampant in the modern world. Dive deeper by reading our article on how sugar is making us sick.

When Glucose Makes Sense

Let’s return to glucose, now. The way I see it, there are three potential use cases for supplemental glucose:

1. To enhance fluid and electrolyte absorption when rehydrating from an illness
2. To enhance performance during intense or extended exercise
3. To help people with diabetes regulate their blood sugar

Since our focus here is to explore everyday hydration and exercise, I won’t cover the third bullet. Consult a medical professional if it applies to you. But let’s talk more about the first two.

#1: Illness rehydration

Glucose is an ingredient in oral rehydration therapy (ORT), a protocol typically used to rehydrate patients with diarrhea. The protocol the World Health Organization (WHO) currently recommends is to dissolve these ingredients in 1 liter, or about 34 ounces, of water:

• 2.6 grams of sodium chloride (salt)
• 2.9 grams of trisodium citrate
• 1.5 grams of potassium chloride
• 13.5 grams of glucose

Some researchers estimate ORT has saved millions of lives. From 1982 to 2003, the death rate from diarrheal illness among children under five dropped by about 50% (from 5 million to 2.5 million) despite similar rates of acute diarrhea. The worldwide adoption of ORT over these years likely helped drive this change.

To what extent is glucose (vs. sodium or potassium) responsible for ORT’s efficacy? Impossible to say. But considering the existing evidence, it’s clear that glucose is an effective rehydration aid during illnesses that produce significant fluid and electrolyte losses.

#2: Exercise performance 

You need energy to power exercise, and this energy comes from burning glucose and fatty acids. Longer, harder efforts require more glucose, which can come from diet or internal stores. Your muscles and liver store about 500 grams of glucose as glycogen, but more strenuous efforts can deplete these stores, hampering performance.

Athletes often use supplemental glucose to offset this decline. In a 2010 Journal of Applied Physiology study, researchers had 12 cyclists ride for two hours, consuming electrolyte waters with varying doses of glucose. Right after the two-hour ride, participants completed a 20-kilometer cycling trial with no access to beverages. Here’s how the different doses (grams of glucose per hour) improved average power output during the subsequent trial:

• 15 g/hour: +7.4% 
• 30 g/hour: +8.3%
• 60 g/hour: +10.7%

As you can see, more glucose led to more power. But what if you want endurance performance without the sugar and resulting glycemic hit?

One option is to consume a low-carb or ketogenic diet. This way of eating helps you become “fat adapted” — it improves your body’s efficiency at using body fat and dietary fat for energy. Read Zach Bitter’s story for inspiration. He broke the American record for the 100-mile race while consuming fewer than 5% of his calories from carbohydrates. It took about a month for him to adapt (energy-wise) to his low-carb diet, according to Bitter.

Less anecdotally, a 2021 meta-analysis of 10 studies found that low-carb interventions didn’t affect aerobic capacity or exercise performance in endurance athletes. This result suggests that dietary carbs (which increase glucose available for energy) aren’t necessarily a performance enhancer.

I don’t use sugar when I exercise, but I see why endurance athletes experiment with intra-workout glucose (I believe the scientific term is “sugary goo”). It’s all about weighing the pros and cons of glucose for your specific situation.

How To Think About Rehydration

For me, glucose’s marginal improvements to hydration don’t outweigh the cons of consuming extra sugar. Your exercise regimen may be different from mine, and it may call for glucose for extra energy. But rest easy on the hydration front — your body is perfectly equipped to replace lost fluids and electrolytes without glucose.

I suggest thinking about rehydration in terms of replacing sweat losses. How much water and sodium are you losing through sweat? Use your estimates to guide your hydration planning. 

If you haven’t explored your sweat rate or sweat sodium concentration before (click to read more in-depth resources), here are some stats to estimate your needs:

• The average sweat rate for 506 athletes under varying conditions was 1.21 L/h. Most sweat rates during exercise fall between 0.5–2.0 L/h.
• The average sweat sodium concentration for the 506 athletes was 826 mg/L, but with plenty of variability. One review pegged the range at 460–1840 mg/L.

So if you’re exercising for an hour, bring about 1 liter of water mixed with 1 gram of sodium (or one LMNT). Drink to thirst before, during, and after exercise, and you’re good to go.

Also, feel free to experiment by bringing 10–20 grams of glucose along with you — it could be worth trying if you’re a serious athlete or fighting a fluid- or electrolyte-depleting illness. We don’t include glucose in LMNT because we wanted to leave that decision up to you. I hope this article gave you a solid framework for making that choice.