Med thumb boston marathon 2009   leading women

Spring is nigh, which means SAD will lift, sun will shine and social media feeds will become a showcase for people who run races and want to talk about it. That's right, photos of neon-clad 5K-ers, mile-time humblebrags and status updates about performance-boosting lifestyle tweaks will infiltrate your newsfeeds. One hot topic, sure to spark many a comment thread, is eating for endurance —  24/7 protein? Pre-race carbo-loading? Well, per the New York Times, a new nutrition study touts the benefits of the “sleep-low” sports diet, which requires ditching carbs come dinnertime.

The concept underlying the sleep-low diet is nothing new. By passing on fresh baguettes and hand-rolled gnocchi at supper, an athlete preps their body to have low carb reserves in the A.M. So, during a morning workout, their body can use fat as muscle fuel. In past research, the Times explains, this particular carb-cutting regimen has shown mixed results in its impact on performance.

But, the new research, published this winter in the journal Medicine & Science in Sports & Exercise, “suspected that the sleep-low diet needed to be integrated into a broader training plan in order to show desirable results.”

By passing on fresh baguettes and hand-rolled gnocchi at supper, an athlete preps their body to have low carb reserves in the A.M. So, during a morning workout, her body can use fat as muscle fuel.

For the study, researchers recruited triathletes to switch up their diet-and-exercise regimens four days a week, for three weeks. The triathletes split into two groups. Half ate a standard sports diet, meaning abundant carbs during meals and after workouts. The other half went on a sleep-low diet. They ate the same amount of carbs, but only enjoyed their doughy delights before dinner. 

All participants also started a new training regimen that included interval-training during the afternoon, “designed to increase fitness and deplete the body’s carbohydrate stores,” and an hour of moderate-intensity spinning the following morning. Everyone could then binge on carbs during breakfast and lunch.

By the end of the trial, the sleep-low group members were “grumbling about evening hunger.” But, they also crushed it, performance-wise, exhibiting marked improvement in simulated triathlon events (which they’d also done before the trial began) including a 10-km race. The nighttime carb-eaters had full bellies, but their athletic performance didn’t improve. And, unlike the sleep-low group, they didn’t lose body fat either.

Taken together, the findings point to the performance-enhancing impact of a diet-and-exercise regimen that goes like this:

  • Workout hard in the afternoon, then avoid carbs afterwards.
  • Train lightly the following morning, then binge on bagels.

Why? Well, the study author suggested that the eating schedule made it easier for participants to burn fat as muscle fuel, which in turn enabled rigorous workouts that made them faster and fitter.