What does the evidence show?
What does the evidence show?
You’d think hydration would be simple: just drink when you’re thirsty, and don’t worry about the details. And maybe it is. That’s the view that gadfly scientist Tim Noakes and others have advanced over the past decade. All those high-tech promises of better or more effective hydration? Just marketing hype from big companies like Gatorade.
And yet, the debates have persisted. That may be in part because the advice to simply drink when you’re thirsty gets a little trickier when you mix in other factors like getting fuel from your drink and dealing with situations—like a marathon—where fluids aren’t always available exactly when you want them. At the American College of Sports Medicine conference earlier this month (whose highlights I’m covering in a series of articles, which started with a look at protein- and muscle-related research), there was, as per usual, lots of debate about some of these nuances. Here are three hydration-related findings that caught my eye.
The most hyped development in sports drinks over the last few years has been the rise of the upstart Swedish company Maurten. Their drinks contain two ingredients—pectin and alginate—that form a hydrogel in your stomach. The hydrogel supposedly encapsulates the carbohydrates in the drink, effectively “hiding” the carbs from your sensitive stomach. That, in turn, lets you down drinks with higher-than-normal concentration of carbohydrate without triggering GI issues.
That’s the theory, at least. Plenty of athletes, including big names like Eliud Kipchoge, are converts. But what’s missing, more than two years after the drink first made headlines, is data showing that you actually burn the hydrogel-coated carbs at a faster rate than normal sports drinks. None of the presentations at ACSM answered that question, but there was some relevant data.
Researchers at the universities of Cape Town, Stirling, and Brighton, led by Cape Town’s Shaun Sutehall, tested Maurten’s effects on gastric emptying—that is, on how quickly the drink moves from your stomach to your intestine. Eight volunteers downed 500 mL of fluid at a time, then sat patiently for the next 90 minutes while their stomach contents were sampled every 10 minutes to see how quickly the drink escaped. The two drinks of interest contained a mix of the carbohydrates maltodextrin and fructose, with or without the hydrogel ingredients. (There was a third drink in the study that tested a different mix of carbohydrates, but we’ll skip those results for simplicity.)
The results showed that half of the hydrogel drink had left stomach after 21.2 minutes on average, while the non-hydrogel drink took 36.3 minutes. That’s a significant difference: the stomach does indeed seem to treat carbohydrates differently when they’re wrapped in hydrogel. But the unanswered question remains the same: does the new drink really enable you to burn more carbohydrates, with less risk of GI upset, than conventional drinks? Until we see a study that directly tracks carbohydrate burning in a head-to-head comparison, my take on Maurten remains: “I don’t know.”
One of the secret ingredients of sports drinks, dating back to the original Gatorade formulation in the 1960s, is electrolytes: substances like sodium and potassium that carry tiny electric charges and are essential for the normal function of your muscles and neurons. As you sweat during exercise, you lose electrolytes, which makes replenishing them essential.
At least, once again, that’s the theory. To be honest, I’ve never seen convincing evidence that taking in electrolytes during exercise makes much difference. Sure, you need to replenish them eventually—but you’ll get plenty of electrolytes with your next meal. During exercise, the most commonly cited danger of electrolyte depletion is muscle cramping, though the exact cause of cramping remains hotly disputed.
All this means I was interested to see a study on electrolytes from a group led by John Caruso at the University of Louisville. They had 34 volunteers do a pair of VO2max tests, cycling on a stationary bike at progressively higher workloads until they reached exhaustion. Before each test, they drank a carbohydrate sports drink; one of the drinks contained electrolytes (magnesium, potassium, sodium, chromium, as well as vitamins C and B-12), while the other didn’t. The researchers hypothesized that the electrolytes would lead to higher VO2max values.
Instead, the results found no differences in performance, heart-rate, or perceived effort with or without electrolytes. To be fair, you probably wouldn’t expect big differences to emerge until you’d been exercising for several hours and had lost a lot of sweat. But the bottom line for now, as the researchers note in their conclusions, is that “little research exists on the ergogenic effects of electrolyte formulations added to carbohydrate beverages.”
One of the innovations Nike’s Breaking2 research team introduced to try to help Eliud Kipchoge and his teammates run a sub-two-hour marathon a few years ago was more frequent drinks. Getting enough carbohydrates in while running as fast as you can for a marathon is tricky, because you’re breathing hard and fluid is sloshing around in your stomach. So Nike’s team decided to offer the Breaking2 runners drinks every 3K or so, instead of the usual 5K intervals, so that the runners could take smaller drinks at each station.
Whether it made any difference or not, Kipchoge, for one, seemed to like it. When he set the world record at the Berlin Marathon last fall, there were drink stations at 5K, 10K, 15K, and then every 2.5K for the rest of the race. Kipchoge used every one of them. (He also had a designated drink handler who cycled ahead to hand him each bottle personally: don’t miss Jonathan Gault’s great post-world-record interview on LetsRun with “Drinks Guy.”)
Does it actually help? A team led by Stephen Mears at Loughborough University in Britain tested the effect of drink frequency by having 12 runners do two 100-minute runs at 70 percent of VO2max, which is a little slower than marathon pace. During one of the runs, they drank 200 mL of sports drink every 20 minutes; during the other, they drank 50 mL every five minutes, for the same total amount.
The results showed that the runners burned more carbohydrate from the sports drink when they drank less frequently. By the end of the run, they were burning 0.67 grams per minute when drinking every 20 minutes, compared to 0.58 when drinking every 5 minutes, a statistically significant difference. That may have something to do with the fact that swallowing larger volumes liquid triggers a more rapid stomach-emptying response than sipping. Their overall carbohydrate burning rates were similar in both runs, which meant that they were using up their limited internal stores of carbohydrate more rapidly when drinking more frequently.
It’s worth noting that comparing 5-minute and 20-minute intervals is a little extreme. For Kipchoge, intervals of 2.5K and 5K correspond to a little more than 7 and 14 minutes, respectively, so any difference in oxidation would likely be more subtle, or perhaps even undetectable. And you have to weigh that against that against stomach and breathing comfort: it may be that it’s worth paying a slight penalty in oxidation rate if the more frequent approach enables you to drink a lot more overall. In other words, like so many hydration-related questions, the basics are clear, but the nuances are still open for debate.
My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available. For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.