Britney Spears reveals the surprising fast food item she's worked into her 'Piece of Me' tour diet (Exclusive)

Britney Spears is gearing up for her tour -- and her workouts are no joke!

ET's Nancy O'Dell exclusively sat down with the pop star in Los Angeles, where she dished all about getting in shape for the North American and European legs of herPiece of Me Tour, tips and surprising tricks included.

"This round of shows that we are doing on tour, they are back to back, so each show is like... I don't have time apart, besides flying," Spears explained. "My show is a workout in itself. It really keeps you strong."

All that time on the road means Spears is hitting in the gym hard before her tour kicks off. Fans have been following the 36-year-old singer's workouts as she posts plenty of videos on Instagram, including some with boyfriend Sam Asghari. But exercise isn't the only way Spears stays in shape. Those rock hard abs are made in the kitchen -- and at a certain fast food restaurant.

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"Sometimes I'm just like, 'I want a hamburger!' but when I'm in work mode, I want [to eat] very clean. I want clean chicken and veggies that's it," she revealed."My stomach is so sensitive, if I have a steak, I will be sick for three days."

"The burger is fine, but I have the small burgers from McDonald's. The happy meal!" she added.

Spears will perform 30 shows in just 51 days, with many concerts already sold out. Cheering her on along the way will be her two sons, 12-year-old Sean Preston and 11-year-old Jayden James.

"They will come with me. They enjoy it," she shared, confessing that Sean and Jayden actually have a little bit of influence over her set list.

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"My kids, they have been putting new remixes into my show and stuff... there is one of the new songs on the radio, and [my son is] like, 'Mom, that is so cool!'" Spears revealed. "So I'm putting all these different new songs in my show, so they are coming along."

Spears' Piece of Me Tour kicks off July 12 at Maryland's MGM National Harbor.

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