Mind & Body

How Important Is It to Refuel Right After a Workout?

When it comes to exercise, there's a lot of questionable advice out there. A lot of it seems reasonable: do crunches to get a six-pack (actually, don't), lay off the running for the sake of your knees (just kidding), stretch to avoid injury (well, there's a right way and a wrong way). One murky piece of advice? Refuel as soon as possible after your workout, or you'll lose all the progress you made. This idea, known as the "metabolic window of opportunity," was once supported by science. But scientists did more digging, and the real truth makes things a little easier on everybody.

To the Window, to the Wall

The idea that you need to eat something ASAP after working out is based on the fact that exercise breaks down muscle fibers and depletes your stores of glycogen, the sugary substance that your muscles use as fuel. The metabolic window is a supposed period of time when your body is primed to absorb the maximum amount of carbs and protein to rebuild muscle and refill your glycogen stores. Wait too long after exercise, and you miss your opportunity.

And like we said, science backed this up — for a while. A 1985 study found that people's bodies absorbed glucose more slowly two hours after a workout than they did earlier. In 1997, researchers found that when they gave dogs protein and carbs directly after running on a treadmill, their bodies absorbed and used it more effectively than dogs who got the fuel two hours post-exercise. A 2001 study found that the same was true of human participants. A study in 2008 went so far as to say that when you refuel is even more important than what you use to refuel.

But other studies have landed on the opposite conclusion, saying that timing doesn't matter or even that fueling beforehand gets better results than fueling after. What's a science-minded fitness buff to do? When there are a lot of studies on the same topic that seem to get differing results, it's time to get out the big guns: a meta-analysis. That's a study of other studies, where researchers collect all the data from all the past studies they can and then analyze it together to get one super-powered result.

That's exactly what famed sports researchers Brad Schoenfeld and Alan Aragon decided to do in 2013. Their meta-analysis found that consuming protein right after a workout had a small but statistically significant advantage over waiting a few hours. But there were a few problems: They found that a lot of that result could be explained by the fact that many of the studies didn't give control groups the same amount of protein as the experimental groups, meaning that those who were fueling directly after workouts were also getting more protein overall. To get to the bottom of things, Schoenfeld and Aragon decided to perform their own experiment.

Related Video: Why Is It so Hard to Start Working Out?

It's the Final Countdown

For a study they published in December 2018, the team asked resistance-trained men to consume a protein supplement either directly before lifting weights or directly after. Those who fueled beforehand were asked not to eat anything for three hours afterward; those who fueled after couldn't eat for three hours beforehand. After 10 weeks of this, the results were a wash: There were no differences in the amount of muscle growth between the two groups. "These findings indicate that any benefits of immediate post-workout nutrition are nullified when protein is consumed prior to the exercise bout," the authors wrote.

This isn't to say that fueling for exercise isn't important — it's just easier to do than metabolic-window proponents would have you believe. In the same way that exercising fasted won't hurt you or help you, when you choose to fuel won't make much of a difference either (although we should mention one caveat: Studies suggest it is a good idea to eat something directly after a workout if you didn't have anything for hours beforehand). As long as you consume enough protein throughout the day, your body will have enough nutrients to rebuild muscle and restock its energy stores. Eat regularly, and you'll be fine.

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You can get plenty of excellent fitness and nutrition information from books by Aragon and Schoenfeld, but one we suggest is "The Lean Muscle Diet" by Alan Aragon and Lou Schuler. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer March 19, 2019

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