THR hears the singer, who will perform on the Academy Awards stage for the first time in 36 years, is on a 21-day regimen -- and just can't decide who should dress her.

This story first appeared in the March 1 issue of The Hollywood Reporter magazine.

Sources say Barbra Streisand, who'll sing on the Oscar telecast for the first time since 1977, has gone on a 21-day cleanse. 

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THR also hears she's having several gowns made and has more than one stylist on retainer.