The body of an NBA player is a finely tuned machine. Every machine, of course, needs plenty of fuel to carry it through a long season on the court. While that typically means eating a lot of lean protein and green vegetables during pregame meals, everyone needs to spice things up now and then.

In most NBA locker rooms, players tend to gravitate towards the same snack. It turns out that one simple sandwich is actually the secret food powering your favorite stars to success.

What does the average NBA diet look like?

Most NBA players eat regularly throughout the day. That’s not to say they’re binging on fast food after practice, though; while there’s plenty of healthy food, each meal is designed for maximum efficacy.

Take Los Angeles Lakers forward Jared Dudley, for example. He begins his day with a breakfast of eggs, complemented by either fresh fruit or oatmeal. After practice, he has a chicken, turkey, or tuna sandwich for lunch. He then takes a nap and has a light snack, which is either trail mix, a salad, or some yogurt. “Steve Nash and Grant Hill have been a big influence on me,” he explained. “They showed me that eating good snacks prevents you from overeating.”

After a dinner of chicken and vegetables, Dudley’s eating isn’t done for the day. There will still be another snack, especially if he’s playing a road game.

The power of peanut butter and jelly

Despite their carefully regimented diets, there’s one meal that NBA players always make time for: a peanut butter and jelly sandwich.

As far as anyone can remember, the first instance of a basketball player publically discussing PB&J came in 2008, when Chicago Bulls guard Ben Gordon explained that he ate the sandwich before taking the court. The ritual truly blew up, however, thanks to the Boston Celtics.

The Celtics, in their quest for a championship, assembled a trio of Paul Pierce, Kevin Garnett, and Ray Allen. One night before a game, one player complained that he was hungry and requested a PB&J sandwich. Bryan Doo, the Celtics strength and conditioning coach, fulfilled the request, and Garnett snagged a sandwich. He played well that night and decided to establish a new routine. “We’re going to need PB&J in here every game now,” he said.

Once the Celtics started eating pregame sandwiches, word spread throughout the league. When players left Boston, they also brought the tradition to their new locker rooms. The meal became such a beloved part of NBA life that the Golden State Warriors even “went to war” with their coaches after a short-lived sandwich ban.

Why eat peanut butter and jelly?

While peanut butter and jelly sandwiches don’t hold that much nutritional value—there is some protein, but also carbs and sugar—there’s a deeper reason why NBA players love the sandwich. It’s a quick and easy piece of comfort in their hectic life.

Basketball players are under constant stress; they get very little sleep and spend more time in airplanes and hotels than any business traveler. A peanut butter and jelly sandwich is a comforting meal that you can have anywhere, at any time. Combine that stabilizing factor with pro athletes’ famous adherence to routine, and you’ve got a hit on your hands.

“You feel good, you play well.” Brian St. Pierre, director of performance nutrition at Precision Nutrition, explained. “Even if we argue that physiologically a PB&J isn’t the ‘best’ pregame meal, that’s only true if you think psychology doesn’t impact physiology, and we know it does. Your thoughts about a food will actually help to shape how your body reacts to that food.”