Oprah Winfrey has not only stayed slim for more than 11 years — down 85 pounds! — but the talk-show powerhouse is in the best shape of her life! How is that possible — and at 53 years old, no less?

“Oprah feels better when she treats herself well,” the star's diet guru, Bob Greene, author of the new book The Best Life Diet, tells Life & Style. “It’s about making positive behavior changes permanent.”

Is anyone having an aha moment?

For more on Oprah's life-changing eating plan — and how you can adopt it, too — check out the latest issue of Life & Style, on newsstands now!