SportingDrinks

Isotonic, hypotonic and hypertonic sports drinks: what the labels mean

Updated . Numbers come from checked labels and cited research. How we check.

Isotonic, hypotonic and hypertonic describe how concentrated a drink is compared with your blood. An isotonic sports drink has a similar concentration and supplies fluid plus fuel. A hypotonic drink is more dilute and puts fluid first. A hypertonic drink is more concentrated and puts carbohydrate first. Carbohydrate content is the main driver.

What “tonicity” means

Every drink has dissolved particles in it: sugars, sodium, potassium, acids and flavorings. The total concentration of those particles is called osmolality (or osmolarity, when measured per liter of solution). Your blood has its own osmolality, and “tonicity” compares the drink to it.

  • Hypotonic: fewer dissolved particles than blood. More dilute.
  • Isotonic: roughly the same concentration as blood.
  • Hypertonic: more dissolved particles than blood. More concentrated.

Concentration matters because it affects how fast a drink leaves your stomach. The ACSM position stand on fluid replacement warns that highly concentrated carbohydrate drinks slow gastric emptying [6]. Jeukendrup’s review makes a similar point: very concentrated carbohydrate solutions can reduce fluid absorption [3]. So the more concentrated your drink, the more it behaves like fuel and the less like fluid.

Why most sports drinks aim for isotonic

The classic sports drink tries to do two jobs at once: replace fluid and supply carbohydrate. The ACSM describes conventional sports drinks as 6 to 8% carbohydrate, and says a drink meant to do both jobs should not go above about 8% [6]. That window is where a drink can fuel you without slowing fluid delivery much.

Percent carbohydrate means grams per 100 ml. Multiply the percentage by ten to get grams per liter, which is the unit our product pages use.

How we classify drinks

Almost no US label lists osmolality, and brands rarely publish lab measurements. So our database estimates tonicity from carbohydrate concentration:

  • below 6% carbohydrate: hypotonic
  • 6 to 8%: isotonic
  • above 8%: hypertonic

It’s an estimate, and we label it that way on every product page. Carbohydrate is the biggest contributor to a sports drink’s concentration, but it isn’t the only one. Sodium and other salts add particles too, which matters in high-sodium mixes. And the type of carbohydrate matters: maltodextrin, a chain of glucose units, adds fewer particles per gram than the same weight of simple sugar. Two drinks with the same carbohydrate percentage can have different real osmolality.

When a brand markets a drink as “hypotonic” or “isotonic,” treat it as the brand’s claim. We report the carbohydrate concentration from the label and the estimate that follows from it, and the methodology page explains the method.

Examples from the database

Here is carbohydrate per liter for a few drinks, mixed as directed:

Compare each figure to the window above. Each product page shows the estimated class directly.

Hypotonic drinks: fluid first

Low-carb and zero-sugar drinks land here, which by our estimate includes many electrolyte tablets, zero-calorie sports drinks, sodium-focused powders and lightly flavored waters.

They suit sessions where you need fluid and sodium but not much fuel. Think a hot one-hour run, a gym session in a warm room, or the parts of a long day when you’re getting carbohydrate from food instead. If you’re heading out for three hours and your only drink is hypotonic, you’ll need your carbohydrate from somewhere else.

Isotonic drinks: fluid plus fuel

The ACSM’s description of a conventional sports drink sits in this middle band. It’s the all-rounder: a reasonable amount of carbohydrate per liter without much delay in fluid delivery [6]. For sessions of one to three hours, a drink in this band can cover a good share of both fluid and fuel.

The catch is scaling. Carbohydrate guidance rises with session length, up to 60 g/h for 2 to 3 hours and up to 90 g/h beyond 2.5 hours [3]. To hit the higher figures from an isotonic drink alone, you’d need to drink a lot of fluid. Many athletes add gels or food instead. The carbs per hour guide walks through the math.

Hypertonic drinks: fuel first

High-carbohydrate endurance mixes sit here on purpose. They deliver a lot of carbohydrate in a small volume, which helps athletes chasing high hourly carb targets without drinking huge amounts.

The trade-off is fluid delivery. A concentrated drink empties from the stomach more slowly [6], so you may need plain water alongside it, especially in heat. Jeukendrup also recommends practicing any high-carbohydrate strategy in training first, to reduce the chance of stomach trouble in a race [3].

Fruit juice and regular soda are hypertonic by the same measure. They aren’t made for drinking mid-session.

Which should you pick?

Match the drink to what you need more of in that session.

  • Need fluid and sodium, little fuel: hypotonic.
  • Need both, for one to three hours: isotonic.
  • Need a lot of carbohydrate in a small volume: hypertonic, with water on hand.

The hydration calculator gives fluid, sodium and carbohydrate targets for your session and shows which drinks fit. For long events, see our best electrolytes for endurance rankings.

Whatever the concentration, drink to thirst. Overdrinking any fluid, isotonic or not, is the main cause of exercise-associated hyponatremia [5].

FAQ

Is Gatorade isotonic?

Gatorade Thirst Quencher has 59 g of carbohydrate per liter, which we compare with the 6 to 8% window the ACSM describes for conventional sports drinks [6]. The product page shows our estimated class. It’s based on carbohydrate, not a lab osmolality test.

Are hypotonic drinks better for hydration?

They deliver fluid with little delay, because they’re dilute. That makes them a good fit when fluid and sodium are the priority and fuel isn’t. In long sessions, though, a hypotonic drink alone won’t supply much carbohydrate, and carbohydrate guidance rises with duration [3].

What is an example of a hypertonic sports drink?

High-carbohydrate endurance mixes, such as Maurten Drink Mix 320 at 160 g of carbohydrate per liter as directed, are built to be concentrated. Fruit juice and regular soda are everyday hypertonic drinks. Concentrated carbohydrate drinks slow stomach emptying [6], so pair them with water.

Is water hypotonic?

Yes. Plain water has almost no dissolved particles, so it’s hypotonic compared with blood. That’s fine for most workouts. It supplies no fuel or sodium, which matters only in longer or sweatier sessions. See our sports drink vs water guide for where that line falls.

Is an oral rehydration solution isotonic?

The current WHO oral rehydration solution is a reduced-osmolarity formula, at 245 mOsm/L [4]. It pairs a modest amount of glucose with sodium and potassium. It was designed for treating dehydration from diarrhea, which is outside what this site covers. For illness, talk to a doctor.

Label data on this page