As a World Wrestling Entertainment superstar who's required to stay in fighting shape year-round, John Cena diet is "boring," he told Bon Appetit in 2018 he usually drinks four glasses of milk with four scoops of meal replacement protein powder for breakfast, for example.

There is, however, at least one exception to his healthy regimen: Before Cena performs, he anxiously eats his way through three boxes of Tic Tacs, he said on "The Kelly Clarkson Show" on NBC, Friday.

Downing the candy is his ritual.

"It's a nervous superstition that I always have before we go on a broadcast," Cena, a 16-time World Champion and one of the highest-paid wrestlers in the WWE, told Clarkson. He typically eats the Tic Tacs about 20 minutes before he has to compete on live television, he said.

"It's pretty much 10,000 calories in straight sugar," Cena said. (In reality, a single mint Tic Tac is only 1.9 calories, and a standard pack contains 60 Tic Tacs, so three boxes would be 342 calories. Plus, Tic Tacs are made with the sugar alcohol maltodextrin, not "straight sugar," as Cena said.)

Cena said the candy is a necessity, given that wrestlers compete in a "small, confined space."

"The ring is 20 by 20 feet, and you're with a group of guys, so you always want to try to smell your best," Cena said. The rigorous WWE touring schedule doesn't always allow for sleep or personal hygiene, so he turned to mints to keep his breath fresh.

In addition to Cena, many other professional athletes and successful CEOs have their own rituals or quirks that they say help their performance.

Retired NBA point guard Jason Terry would always eat fried or rotisserie chicken before games, for example. "I can't deviate from chicken," he told the The New York Times in 2013. "It has to be chicken."

Other rituals have nothing to do with food. Jeff Bezos has a pair of lucky cowboy boots that he wears when his space company, Blue Origin, has test flights. Similarly, tennis champ Serena Williams reportedly wore the same pair of socks throughout the course of a tournament, the The New York Times reported in 2013.

And golfer Tiger Woods always keeps three tees in his right pocket for good luck, and marks his golf balls with a quarter from the year his dad was born, 1932, he told Golf Digest in 2019.

Research actually supports these idiosyncrasies, even if they seem random. A 2014 study found that following a superstition or having a lucky charm improves people's self-efficacy, or their belief that they can perform. When people have higher self-efficacy, they tend to set more ambitious goals and persist at them.

Another 2018 study out of the Kellogg School of Management at Northwestern University found that people take more risks when they engage in a superstitious act.

Disclosure: NBCUniversal is the parent company of NBC and CNBC.

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John Cena's 'nervous superstition' is eating 3 boxes of this candy before a WWE show - CNBC