Kellan Lutz "Had to Stop Eating" for Calvin Klein Underwear Ads

How did Kellan Lutz prep for his sexy Calvin Klein underwear ads?

"I had to stop eating so...." he joked to UsMagazine.com at the Calvin Klein collection fall 2010 party in NYC Friday. "I love candy, and I think that's where I could be super ripped if I didn't eat so many gummy bears. So, I cut back on those, and I just swam and boxed as much as I could."

Check out more photos of stars showing off their under garments

Lutz, 24, continued, "And I started training parts of my legs that I hardly ever trained really. I tried to bulk up to make the underwear look good."

The workout paid off.

See more stars gone shirtless!

"I have my mom's best friends proposing. Some are actually quite attractive, so I might hold on to those numbers and emails that are quite flattering," joked Lutz.  (What does on-again fling AnnaLynne McCord think of the ads? “[They’re] pretty sexy,” she told Us.)

Lutz says he "can't wait" for the billboards -- which also feature True Blood star Mehcad Brooks, Spanish tennis star Fernando Verdasco and Japanese athlete Hidetoshi Nakata -- to hit streets March 1.

"It was always a dream of mine to have my mug, whatever it was... I didn't think it'd be for underwear, but I'm quite happy for it. I'm just very thankful," Lutz says. "I know it really helped Mark Wahlberg's career, and I can only hope that I get half as much of a chance.

"And, you know, having Twilight open doors and having Rob [Pattinson] and Taylor [Lautner] and Kristen [Stewart] being the faces of the franchise, and the rest of us float under the radar, this will hopefully allow me to have my time," continued the New Moon star.

"Hopefully seeing myself in skivvies will allow me to have some awesome action movies coming my way. I'm really excited."

See Twilight stars before they were famous!

Lutz says he had a "great time" at the shoot because he "felt great in [his] underwear."

The one potential issue?

"Now my nude a*s is going to be all over billboards, we'll see what my mother thinks," he laughed to Us earlier this month.