Kate Walsh shows off her bikini body at the beach in Miami Beach, Fl on December 11, 2012. Credit: Jackson Lee/Juan Garces

Kate Walsh has been hiding a super-fit figure under her TV scrubs!

The Private Practice actress showed off her sexy, athletic beach body on in Miami Dec. 13. Joined by her boyfriend of 16 months, Chris Case, the 45-year-old redhead looked sensational wearing a black string bikini.

Earlier this year, the Grey's Anatomy alum shared her diet and fitness secrets with Us Weekly. "Everything changes as you get older. I recently started changing my diet, not to diet, but to feel better. As crazy as it is, I'm eating for my blood type a little more," the star revealed. "I still allow myself to cheat when I go out to dinners or on the weekends, but I'm trying to stick to mostly vegetarian [fare]. I feel better and I have more energy."

Walsh's favorite foods include lentils, quinoa and "raw broccoli with salt, pepper and olive oil. I sear the shizzle out of it!"

The Perks of Being a Wallflower actress doesn't stick to one exercise to stay in shape. "I walk, I do Pilates, I do ballet . . .terribly!" the actress laughed. "I walk around the Silver Lake reservoir [in L.A.]. . .I try to get out. I like the fresh air."