What does the evidence show?
What does the evidence show?
During the 19th stage of this year’s Giro d’Italia, Chris Froome launched a punishing 50-mile solo breakaway, erasing a three-minute deficit in the overall standings on his way to his sixth Grand Tour win. The stunning ride raised eyebrows given the controversies surrounding Team Sky’s alleged rule-bending and Froome’s own positive test for excessive levels of an asthma drug the year before. Team Sky’s response: a data dump that unveiled the hyper-meticulousness of their sports nutrition plan. Froome’s breakaway, they suggested, was enabled in part by a newly developed sports drink they called “rocket fuel” and an overall fueling regimen that involved downing 6,663 calories and the carbohydrate equivalent of 85 slices of bread that day.
Can getting your nutrition right spur you to otherwise unattainable athletic heights? If you tune into pervasive advertising campaigns from players like Gatorade, the company that basically invented commercial sports nutrition, or even the dairy industry, who’ve improbably managed to establish chocolate milk as a performance-boosting recovery drink, the answer is definitely yes. Others have been more skeptical, though. A scathing review in the British Medical Journal in 2012 characterized the current state of knowledge about sports drinks as “forty years of sports performance research and little insight gained.”
The truth, as is usually the case, seems to be somewhere in the middle. There’s plenty of snake oil out there; but there has also been remarkable progress in understanding the complex metabolic links between what you eat and how you perform in training and competition. In a recent issue of Science, two of the top sports nutrition researchers in the world present a detailed seven-page overview of the current state of the art. Louise Burke is the longtime head of sports nutrition at the Australian Institute of Sport; her husband John Hawley directs the Exercise and Nutrition Research Program at Australian Catholic University.
Their review is free to read online; if you’re interested in the topic, I highly suggest you check it out. As a teaser, here are three of the key themes they identify in modern sports nutrition (followed, as a bonus, by three interesting or unexpected nuggets that grabbed my attention):
What should athletes eat? That depends on what they’re doing, Burke and Hawley argue, notwithstanding the “enduring belief in a single, superior ‘athletic diet.’” The clichés of the pasta-fueled marathoner and the steak-fueled football player are familiar, but the authors identify 11 distinct sub-types of fatigue along with appropriate nutritional countermeasures.
For example, if you’re in a team sport like soccer with repeated short, high-intensity sprints, one of your key fuel limitations may be the recovery of phosphocreatine stores in your muscles between sprints; you can fight that by taking creatine. In a middle-distance event lasting for a few minutes, rising acidity in your muscles is a problem, and baking soda or beta-alanine may be the solution. Whatever your sport, you need the appropriate nutritional tool for the job.
Probably the biggest change in sports nutrition guidelines over the past decade or two is the recognition that every day is different. You might need more carbohydrate and more calories overall on a heavy training day compared to a light training day, but similar amounts of protein. On a longer timescale, you might tweak your diet to bring down your weight as a peak competition approaches. The result: depending on the athlete and the training cycle, a sports nutrition plan might call for anywhere from 2 to 12 grams of carbohydrate per kilogram of bodyweight—a massive range rather than a simple recommendation to eat the same thing every day.
Beyond simply providing fuel, the food you eat can also amplify (or blunt) the adaptations triggered by training. Another form of nutritional periodization involves workouts performed with deliberately low energy stores, which trigger larger-than-normal cellular responses. The problem is that “training low,” as this tactic is called, also places greater stress on your body, raising the risk of illness and overtraining. That means you have to think very carefully about when you use this kind of approach—or, to put it another way, you have to periodize it.
The 2012 BMJ article that criticized sports nutrition research was authored by “epidemiologically trained scientists,” familiar with the techniques needed to tease out generalizable patterns in large populations. But sports nutrition, particularly at the elite level, will never meet that threshold. “The individuals who contribute blood, sweat, and tears to scientific investigations,” Burke and Hawley note, “are at best well trained, often male, and almost always subelite.” You can’t run a study with 1,000 Olympic finalists in it, because there simply aren’t that many Olympic finalists.
It’s also not enough to ask whether, say, carbohydrate drinks boost performance. You have to ask how carbohydrate intake interacts with fluid intake, other substances like caffeine and baking soda, and environmental conditions like heat, altitude, and time of day. As a result, the highest quality of evidence—randomized controlled trials focused on a single intervention in a large population—may end up giving athletes “generic information inappropriate for a specific task.”
Instead, Burke and Hawley argue for “bespoke solutions” that are tailored to a given sport and competitive context and to the athlete’s individual experiences and responses. Interestingly, that’s not far from what the BMJ critics also concluded: “Through our analysis of the current sports performance research, we have come to one conclusion: people should develop their own strategies for carbohydrate intake largely by trial and error.” The difference is that Burke and Hawley believe that we know enough to make some pretty good starting guesses.
While a big-picture review like this mostly focuses on broad themes, there were some intriguing details too.
Over the years, I’ve written several times about research showing that you can boost your performance by swishing a sports drink around in your mouth then spitting it out, essentially tricking your brain into thinking more fuel is on the way. It’s a technique you now see athletes using late in marathons, triathlons, and cycling races (and even at the World Cup).
That’s just the tip of the iceberg, it turns out. Burke and Hawley note similar “mouth sensing” research beginning to emerge with water (for thirst) and caffeine. There’s also menthol rinse to make you feel cool in hot conditions; bitter-tasting quinine to jolt the autonomic nervous system before sprints; and various chemicals like capsaicin that may trigger receptors that disrupt or prevent muscle cramps.
The sports supplement market, according to a report cited in the paper, generated $9 billion in 2017—and that doesn’t even include protein powders. And this total is forecasted to double by 2025. What do athletes get from this enormous investment? In some cases, they get positive doping tests thanks to accidental or deliberate contamination of a supposedly permitted supplement. There were also 23,000 emergency department visits caused by dietary supplement use in 2015.
But most often, they get nothing. From the very, very long list of supplements that purport to either enhance performance directly, or enhance it indirectly through better recovery or body composition change, Burke and Hawley flag only five as having “robust evidence of efficacy”: caffeine; creatine; baking soda and beta-alanine to buffer acidity in the muscles during intense exercise; and nitrate, the key ingredient in beet juice, to improve the efficiency of muscle contractions.
If Chris Froome’s meticulous Giro fueling plan represents the acme of modern scientific sports nutrition, it’s important to also consider the opposite end of the spectrum. Runners from East Africa have absolutely dominated distance running in recent decades, but Burke and Hawley point out several clashes between sports nutrition orthodoxy and the typical dietary patterns of East African runners: “reliance on vegetables (80 to 90 percent of diet) rather than animal food sources, very limited food variety, distribution of energy to a small number of meals in the day, and chronic periods of low energy available.”
Are Kenyan and Ethiopian runners successful because of, or in spite of, their nutritional practices? We simply don’t know, and it’s important to realize the limits of our current knowledge.
In fact, as Burke and Hawley readily acknowledge, sometimes athletes really do know better than scientists. For years, scientists recommended taking 6 to 9 milligrams of caffeine per kilogram of bodyweight an hour before competition—so Burke and her colleagues couldn’t understand why elite cyclists were so fond of drinking flat cola toward the end of races, since the caffeine content of 1 to 2 mg/kg was too small to boost performance. Finally, to try to convince the cyclists the change their habits, they ran a scientific study—and found that the lower dose, taken during the race, really did help.
The nutritional recommendations were updated accordingly. And not, you can be sure, for the last time.
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.