Julianne Hough** has never looked hotter -- or happier!

On Jan. 2, the Safe Haven actress, 24, rocked a white string bikini while paddle boarding in St. Barts with Ryan Seacrest**, 38, her boyfriend of nearly three years. Looking toned as ever, the bubbly blonde was all smiles as they navigated the blue waters.

Staying active is important to Hough, who is also a professional dancer and singer. "I get bored quickly. I like to switch it up. Right now I'm loving SoulCycle. I'm doing that with some friends," she recently told WebMD magazine. "It's not only a great workout and you sweat your butt off -- I just love the instructors. They're so uplifting, motivational and inspirational that by the end of it you want to cry, you're so inspired, and you feel like you can conquer the world afterward."

Hough -- who recently began taking ballet classes -- also swims regularly. "Instead of doing laps I'll add paddles to my feet or hands, and try to swim in place, almost like a water aerobics kind of thing," she revealed.

In October, the Rock of Ages star jokingly blamed her boyfriend for making her gain 20 pounds since they began dating in 2010. Luckily, Hough said, "I'm like my mother: I distribute my weight evenly. I look like I've gained 5 pounds but I've actually gained 20."

To slim down, Hough told WebMD, "The first thing I do is I cut out alcohol, especially wine, completely. I stop the sugar and white, flour-based carbs. I'll add protein shakes some days; maybe the next day a green shake or drink. I like to mix it up."

Seacrest, meanwhile, stays trim by regularly drinking Brazilian Thunder smoothies. "My trainer, Jeff Deperon, turned me on to this," he once said on Jimmy Kimmel Live. The green juice consists of kale, coconut water, collard greens, cinnamon, ginger and "a little bit of lemon."

"I literally drink this first thing in the morning and I drink it before I go on American Idol," the KIIS-FM deejay said. "It's really good for you and it keeps your energy up."

This article originally appeared on Usmagazine.com: Julianne Hough Shows Off Fit Bikini Body, Paddle Boards With Shirtless Ryan Seacrest