What's the Best Sports Drink for You?

Isotonic, Hypotonic, Hypertonic, or Gin & Tonic? (Pro tip: Probably not the last one.)

The Upshot, Upfront:

• For efforts longer than an hour, science says you’re better off with a hypotonic sports drink containing electrolytes and a little sugar.

• For shorter and/or easier efforts—and when not working out—drink water!

When we discussed electrolytes a few weeks back, I breezed over the importance of osmolality in sports drinks. Today, I correct that and fill in the blanks.

TBH (my daughter says this all the time, so it must be cool), I’m not thrilled about writing on this topic. Personally, I find it fascinating. Yet, whenever I bring osmolality up in an article, lecture, or wedding speech, eyes tend to glaze over—and being boring is my worst nightmare.

Unlike most neurotic writers, I don’t have insecurity dreams where I show up to school without pants. Rather, I have insecurity dreams where I take off my pants at school in a desperate bid for attention.

But, umm, anyway, yeah... osmosis. If you know about this, it’ll help you pick a better sports drink, so let’s get some science on.

Stop being insecure and just tell us what osmosis is.

IMHO (another gem from my daughter), once you break down osmosis, it’s easy to understand.

When fluids are separated by a semi-permeable membrane (your gut lining, in this case), the fluid with less dissolved particles (meaning it’s less concentrated) will cross the barrier to where the fluid with more dissolved particles (meaning it’s more concentrated) in an attempt to restore balance. Osmolality refers to the number of dissolved particles in a fluid. It uses a unit of measure called milliosmoles. For example, human bodily fluids, including blood, have an osmolality between 280 and 295 milliosmoles per kilogram (mosmol/kg).

What does osmosis have to do with sports drinks?

Lots! Your body loves balance and it uses osmosis to achieve it. Generally, a good sports drink is formulated with the osmolality of your blood in mind. That way, it can use the process to pull as much water into your system as possible.

You’ll find three types:

Hypertonic: A drink with more dissolved particles (sugar and electrolytes) than there are dissolved particles in your blood.  

The problem with hypertonic drinks is that they have osmosis working against them. Not only do they absorb slower, but they can actually pull water out of your system and into your intestines, dehydrating you in an effort to create a balance between fluids.

What’s more, all that unabsorbed liquid in your stomach can slosh around (yes, “slosh” is actually the term scientists use), causing gastric upset. If you ever slammed a 16-ounce bottle of neon blue sports drink in the middle of a hard effort and suddenly felt like you were going to lose it (or actually lost it), this is probably why.

Hypotonic: When a drink has less dissolved particles than your blood, thus using osmolality to their advantage. These drinks typically contain around 200-250 mosmol/kg of particles. Most of the time, those particles are sugar and electrolytes, but some drinks just have electrolytes.

Don’t fear that sugar! It helps the body absorb both water and electrolytes. Also, a small amount of sugar, while intended to aid absorbency, still provides a little fuel, which isn’t a bad thing for longer efforts.

Isotonic: When a drink has an equal amount of dissolved particles to you blood.

The goal of isotonic sports drinks is to maximize carbs (for fuel) without the absorbency issues of hypertonic drinks. It’s a tricky needle to thread.

Which one is best?

The best sports drink for you is the one that works best for you. If you already have something that works, there’s probably no reason to change. However, if you’re osmo-curious, I generally recommend hypotonic sports drinks for long efforts. The science bounces between hypotonic and isotonic, but this 2021 systematic review of 28 studies in the journal Sports Nutrition is pretty compelling—and informative. It concludes, “Hypotonic carbohydrate–electrolyte drinks ingested continuously during exercise provide the greatest benefit to hydration.”

I also base my recommendation on personal experience working with athletes—and deliberately making poor hydration choices in my own training just to see what would happen.

Of course, there are exceptions. For example, if you’re not really going to try too hard but you know you’ll be sweating a lot, a hypotonic, electrolyte-only drink might be better. Or if you’ve bonked and you desperately need carbs, you’re probably better off with a hypertonic drink. I’ve been known to administer a Coke in these situations.

The best hydrator for all other situations…

The OG performance hydration solution is pure water. This tasty beverage should be your go-to almost every moment of the day that you’re not hammering a prolonged workout. If you’re doing a sub-hour effort, a long-but-easy effort, or just living your general life, there’s really no need for sports drinks, regardless of osmolality.

Although the occasional G&T might be okay, if that’s your jam.