Dr. Stacy Sims.
Dr. Stacy Sims.

Is Your Hydration Drink Making You Dehydrated?

A conversation with Dr. Stacy Sims, endurance runner, Ironman triathlete, and pro-elite road racer who has been studying the science of performance and nutrition for two decades

Dr. Stacy Sims.

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When Osmo Nutrition launched last summer, it was hard not to roll our eyes. “Do we really need another sports nutrition company?” we wondered. There are already more sports drinks on the market these days than there are soft drinks. But Osmo, we discovered, is taking a different approach than other sports nutrition companies.

The side of every pouch of powdered hydration mix that Osmo sells bears the stamp, “Based On Peer-Reviewed Science.” The company’s trio of drinks was developed in large part from the research of Dr. Stacy Sims, an endurance runner, Ironman triathlete, and pro-elite road racer who turned her attention to the science of performance and nutrition two decades ago. Through her research at the Stanford School of Medicine as well as her work with a number of professional cycling teams, including Garmin-Slipstream, Sims came to a surprising conclusion: Not only are most of the sports nutrition drinks on the market not optimized for best hydration, but many of them are actually impeding athletes’ performances. From that realization, Sims launched Osmo as a better alternative. The company’s primary tenet—food in the pocket, hydration in the bottle—might seem obvious, but it’s a broad departure from much of today’s conventional liquid food wisdom.

We have been experimenting with Osmo for six months, and in December we spent a few days with Sims testing the product against competing nutrition offerings. Afterward, we sat down to review the science and to ask Sims to explain how Osmo is different from everything else out there on the market.

In a nutshell, what is Osmo?
GI problems, cramping, and difficulty recovering plague endurance athletes. As an athlete and a scientist, I had the opportunity to figure out the “why” to many of these problems. Osmo is my way of sharing with the general athletic population the past 20 years of research I’ve done. It is my goal to have people race without the worry of hydration and nutrition.

You worked with the Garmin-Slipstream Pro Cycling Team at the outset of this project. Describe your work with them and what sort of results you saw.
Back in 2009 I was working on a contract to help develop a new hydration product. The project manager mentioned that the sport scientist at Garmin was struggling to help his riders overcome GI problems, dehydration, and cramping. Like a lot of top athletes, the Garmin riders were having real performance and GI distress issues related to the products they were drinking. I had been doing research in this field for the better part of a decade, so I reached out and was invited to help create a hydration solution for the riders during a lead-up camp to the Tour de France. In those three weeks, I developed an initial formula and it was quickly adopted, not only by the Garmin riders but by others who could get their hands on it.

During the development I tracked hydration status (team riders had to pee on sticks even during rides), GI comfort, power output, and overall training stress. Ultimately, by using the new formula we saw a reduction of the rate of dehydration, increased power (or rather, lack of decline), no cramping, and no GI problems. Performance and recovery dramatically improved for these elite pro guys.

When I got home and started implementing this formula with my Cat 2-3 cyclists, Ironman, and female athletes, I found there were a few problems with regards to sugar ratios and potassium. I tweaked the formula to suit the needs of a wider population, and that modified formula became Osmo Active.

In the simplest terms, Osmo’s system comes down to food in the pocket, hydration in the bottle, right? Why?
Hydration and fueling are both critical to performing your best, but separating the two is the most effective way to address each need. There are so many “liquid calorie” options on the market that purport to take care of an athlete’s hydration and fueling needs all at once. The focus of most of these products is carbohydrate replacement (i.e. getting carbs into your body to keep energy up). The problem is that these “liquid calories” actually slow the absorption of liquid into the body. Often, by drinking calories, an athlete is hindering his or her body’s ability to hydrate.

You’re saying that liquid calories can actually lead to dehydration?
Yes, but you have to understand to the whole process to see why.

During exercise, your core temperature increases and your body works to regulate the temperature by offloading heat through sweat. This means you are constantly losing water and salt through evaporation. As a result, the watery part of your blood also drops, and the blood becomes more viscous, which leads to a higher heart rate, increased core temperature, and lower power production—i.e. reduced performance.

There’s also a competition within your body for blood: Blood goes to the muscles for metabolic function; blood goes to the skin to get rid of the heat produced by the working muscles. As body water drops, this competition increases, and the blood flow to the skin takes precedence, primarily because heat is a greater threat to the body than keeping the muscles working. The fatigue you experience is a result of the drop in blood flow to the muscles. Also, the contractile proteins in your muscles stop working when the muscle temperature rises above 102 degrees Fahrenheit.

It’s possible to counteract these body temperature and blood volume issues through proper hydration, but this is where the problems with liquid calories begin. There are two key factors for keeping the blood fluid and supplied to the muscles. First, you need what you are drinking to be less concentrated than your blood. (Technically speaking, it needs to have a lower osmolality, which is the measure of solutes in a solution. Blood sits around 285mOsm.) Second, you want what you are drinking to have substances that facilitate fluid transport: the intestinal cell membranes use sucrose, glucose, and sodium as facilitators to get fluid across the cell membranes.

The typical sports drink has five to six percent carbohydrate solution and osmolality of 300-305mOsm. Given that this is a higher solute concentration than in blood, the body’s physiological response is to pull water from the vascular system to dilute the substance. So water moves out of the blood and muscles, which causes dehydration, and into the stomach and digestive system, which causes GI distress. And even though many sports drinks include sodium and sucrose, which should aid in fluid absorption, the higher osmolality of the drinks means the sodium and sucrose actually facilitate fluid movement into the intestinal tract rather than out of it.

A carbohydrate solution of five to six percent is not enough energy to sustain endurance exercise. (You want three to five calories per kilogram of body weight per hour of mixed macronutrient food.) Beyond that, in addition to sucrose for carbohydrate, most sports drinks use maltodextrin and fructose, both of which cause GI distress and increase heat storage as they are broken down (meaning a faster rate at which your core temperature rises). Finally, in the intestines (where 95 percent of water absorption takes place), maltodextrin inhibits positive water flow into the body by pulling water back into the intestines.

That may sound complex, but the upshot is simple. Sports drinks with a carbohydrate concentration of five percent or more and with fructose or maltodextrin actually lead to dehydration.

How does Osmo Active Hydration work?
By keeping the solute concentration lower than the osmolality of the blood, Osmo capitalizes on the body’s physiological response to pull fluid out of the GI tract and into the places it needs it, namely the blood and the muscles. Osmo’s glucose-sucrose ratio plus the sodium citrate in the formula actually increases fluid absorption, which keeps your body temperature lower and your muscles functioning. And because you don’t have all that fluid in your GI tract, you’re a lot less likely to have bloating and gastrointestinal distress that come with higher concentrated sports drinks.

In December, we did some testing to compare the Osmo approach with a more standard hydration and nutrition approach. Can you describe the testing process?
We did two days of testing with specific standardization before each test (same diet and workout regimen). The trials were randomized to prevent bias: you consumed Osmo and solid food during one trial, and liquid calories on the other, but the order was determined through random selection. The trial itself: 60 minutes steady state at 70 percent of FTP followed immediately by a 15-minute time trial. The outcomes of interest for comparison were all objective: power output with core temperature rise, skin temperature, sweating efficiency, and hydration status at the end of each 15-minute trial.

And what did my tests show?
We demonstrated that you got faster (i.e. greater power output) on Osmo while maintaining a lower body temperature and staying better hydrated. This is an especially important consideration for ultra-endurance events like the ones you do: less stress on the body means you can keep going at a greater work output. I have a collation of tests from many athletes that show similar results to yours.

So if Osmo is only for hydration, what should you be eating for fuel?
Real food! With the separation of fluid and fuel, you can tailor your nutritional needs to your sex, your training, and racing conditions (for instance duration, altitude, temperature). Real food is just that: sweet potato, small sandwich bites, low fat brownie or cookie bites, salty pretzels. Even a PayDay bar will work—maybe it’s not “real” food, but it’s tasty and a fast, easy fix in the convenience store.

If it’s true that most hydration drinks actually lead to dehydration, why do manufacturers continue making them?
Excellent question. Remember: The number one best-selling hydration drink on the market stems from a quick solution on a football field over 40 years ago. Based on that quick fix, a product was put on the market. In effect, they came up with a product that had a five to eight percent solution, and then they subsequently sought out the science to prove the effectiveness of the drink. The short answer to your question is marketing and dollars. There are lots of studies out there showing that a two to four percent solution gives the greatest hydration boost, but large corporations with strong marketing campaigns have power to get those studies labeled as anomalies.

Why aren’t more companies getting on this low-concentrate bandwagon?
There is already another existing product out there, which was my original formulation from the Garmin Tour de France camp. And there is a trend of low-concentration products coming out. For example, NUUN and Camelbak Elixir tablets are one of the fastest growing drink forms. While these are not truly optimized for rate of fluid abosorption, they are better alternatives than the high sugar concentrates in most existing drinks. I have spoken with multiple established brands in the sports drink market, and they know this is the right science and are changing directions to emulate our product. The day is not far off when all serious hydration products are around a three percent solution, like Osmo Active. The wave is coming.

In addition to the Active Hydration product, Osmo also makes PreLoad Hydration. What is this and how does it work?
PreLoad is a specific formulation intended for use prior to hot events, time trials, and high-intensity efforts. It works on the concept of hyperhydrating, which effectively means that you go into an event with extra body water. PreLoad increases blood plasma volume by between 15 and 20 percent, and that extra fluid in your body slows down the rise in your core temperature and therefore slows the onset of fatigue and power loss. It also increases total body sodium stores ahead of an event, which staves off cramping longer. We recommend consuming PreLoad both the night before and the morning of an event to ensure you are optimally hydrated before an effort.

And what about Acute Recovery? How is it different than other recovery drinks out there?
Acute Recovery is what you drink after exercise. It is comprised of a 2:1 protein to carb ratio with 30mg of caffeine. Yes, that’s completely different than competing formulas—hold that thought! The idea here is to have a high-quality protein with carb and caffeine: The protein (whey isolate and micellar casein) shuts down the breakdown from exercise, carbs (dextrose from grape sugar) provide glycogen, and the caffeine in conjunction with carb and protein has been shown to enhance glycogen replacement by 66 percent over carb and protein alone.

Now, most other recovery drinks are 4:1 carbs to protein so why the ratio discrepancy in Acute Recovery? Mostly, sex differences. Women need a 3:1 carb to protein mix, while men need a 4:1 ratio. The hardest thing to find post-training is a high-quality protein, so we have loaded up Acute with this. Carbs are easy to find, and most people will be taking more of them in anyway. So you can tailor your recovery drink with almond milk or another source of carbs specifically to maximize the benefits in that 30-minute post-exercise window.

Another critical factor is we do not put antioxidants in Acute Recovery—purposely. Taking in antioxidants close to the end of training and within the acute recovery window (three to five hours) actually diminishes what you’ve accomplished with exercise because it kills key feedback to the mitochondria for adaptation.

Lots of racers will be skeptical of Osmo because they have been using liquid food successfully for years. You know what they say: “If it ain’t broke….”
I get this question a lot. First, you need to consider what comprises the liquid calories you’re taking in: maltodextrin inhibits fluid absorption; fructose increases heat storage; chloride alters the membrane potential of the intestinal cells, releasing endotoxins. All of these contribute to undue stress, which your body has to overcome to perform. If you eliminate these extra stressors, your body can focus on the task at hand, and without that extra stress your performance will improve.

This idea of liquid calories is old nutrition science. Sure you might be able to get by with it. But based on my research and plenty of peer-reviewed science—as well as lots of practical in-field testing—your performance in training, racing, and recovery will significantly improve by separating your hydration and fueling needs. Until you try it, though, you won’t know how much better you will feel and perform.