The New Science Behind Low-Carb Training
Runners who do intense workouts on no carbs tend to experience weakness, fatigue, and poor performance. But a new strategy called “sleeping low” might give athletes the same edge—without the suffering.
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University of Copenhagen sports physiologists first developed the “train low, compete high” protocol in 2005 for athletes looking for a performance edge. It encouraged the idea of double workouts every second day. In practice, athletes would eat breakfast to fuel their morning session, then skip lunch prior to their evening session, leaving muscles depleted of their glycogen stores.
The benefits were thought to be pretty straightforward: you force muscles into using glycogen stores more resourcefully by tricking them into becoming fat-burning machines. Dipping into fat reserves would prevent glycogen stores from depleting completely, so you’d lower your chance of “bonking,” or running out of fuel, during a long endurance race.
But the dietary protocol hasn’t stood up to the hype. “After over a decade of scientific research on ‘train low’ protocols, there have been no clear demonstrations of improved performance with competitive athletes at an elite level,” says Louise Burke, a professor of sports nutrition at the Australian Institute of Sport.
Quite the opposite, Burke has found evidence that chronically training low on carbs for an extended period can hamper our muscles’ ability to use carbs eaten before competition. “What we thought was ‘glycogen sparing’ may have been ‘glycogen impairing,’” according to Burke, who wrote about her concerns in a 2010 review in the Scandinavian Journal of Medicine and Science and Sports.
The sleep-low protocol allows athletes to spend only their non-waking and early morning hours in a glycogen-depleted state. That way they won’t feel awful all day and during their evening workouts.
Most competitive athletes—including those in team sports who train low on carbs—end up “feeling terrible,” especially when they see themselves losing performance gains, adds John Hawley, a professor and head of the Exercise and Nutrition Research Group at Australian Catholic University, and Burke’s husband. Carbs are crucial for the intense movements often required of competitive athletes, he said. Most athletes are at their best and train hardest in the evening generally, so to withhold carbs before their evening practice can crush their progress.
Enter the concept of sleeping low, a new strategy under current study at Hawley’s lab and in Europe. Sleeping low promises to succeed where training low has failed. The new protocol works just as it sounds: Athletes train hard in the evening and go to bed fasted. (Or without eating carbs at dinner—that means no pasta or dessert.) So their muscle glycogen stores stay depleted throughout the night. The next morning, athletes train lightly on an empty stomach—that’s where they force their muscles to adapt to burning fat. Then, it’s just refuel and repeat.
The underlying rationale is to not compromise power and intensity during the evening training session, Hawley says. The sleep-low protocol allows athletes to spend only their non-waking and early morning hours in a glycogen-depleted state. That way they won’t feel awful all day and during their evening workouts. Skipping breakfast to train lightly in the morning should be easier for most athletes and can teach muscles to use fat as fuel as needed, while the new protocol still allows for use of fast-acting sugars in the evening to avoid sacrifices in form and performance.
Competitive athletes should know better than to risk avoiding carbs completely, Burke says, adding that she’s frustrated that some popular authors, or “low-carb exercise gurus,” as she calls them, profess to know better than what the current research supports. After all, when muscles need fast fuel for quick, powerful movements, they need carbohydrates. When nerves are shot over an intense competition, they need carbohydrates to recover. And when the immune system is in a vulnerable state after a hard workout, it prefers carbs for rehab.
Sleeping low, researchers hope, might be an ideal way for endurance and team-sport athletes to balance their carb and fat needs, while improving performance. The goal here is “metabolic flexibility,” Burke says. “It shouldn’t be carb team versus fat team, because there are no blacks and whites.”