By Emily Feimster Mariah Carey recently lost 30 lbs, Kirstie Alley dropped a whopping 75 lbs, and even Janet Jackson is back to her six-pack after reportedly gaining a lot of weight for a movie that never happened. These celebrities, like many, are realizing the importance of being fit, not only for the futures of their careers, but also for their futures in life.

"I think a lot of people in the spotlight realize that part of their total package is not only their talent, but also how they look. It's more than just changing a hairstyle. Changing your body changes how you move, how you're seen, and how you see," says personal trainer to the stars, Gunnar Peterson, who has worked with Ben Affleck, Jennifer Lopez, Scott Foley, and Bruce Willis, to name a few.

Former N'SYNC boy band member Joey Fatone, whose nickname has been Fat One, said one of his reasons for signing up for "Dancing With the Stars," was to shed the pounds he's packed on since his days of dancing with Justin Timberlake. Already he's finding his dance outfits to be big a little too big. However, he's not the only guy who'll be looking svelte on stage. "American Idol's" Taylor Hicks has gone from 215 to 193 lbs since winning the popular reality show last year. He stopped eating fast food and now sticks with salads, brown rice, fish, and chicken noodle soup. He also runs for 45 minutes every other day to stay in shape.

Josh Peck of the popular "Drake & Josh" series took dieting a step further by dropping over 100 lbs through yoga, meditation, karate, and having a personal trainer. "I made a conscious effort to lose weight because I knew I could be happier as well as being healthier. I feel that because I do so much children's television, I am a better role model," Peck has stated.

Of course it takes a lot more than exercising to be well balanced. "You've got to make good choices outside of the gym. The celebrities I train are eating right, hydrating themselves, and getting enough sleep. You've got to commit to it. It is a lifestyle," Gunnar points out. "You don't turn down everything that comes your way that sounds like fun, but you do have to make some active, good choices."

Being good certainly comes easy to Oscar winner Jennifer Hudson, who was encouraged to lose weight during her stint on "American Idol" and then asked to pack on extra pounds for "Dreamgirls." The star, who has since lost an undisclosed amount of weight, admits she doesn't go to clubs, drink alcohol, or smoke. She wakes up at 4:00 a.m. to run for an hour, followed by an hour-long workout in the gym with her trainer. Now that's dedication!

Hudson's co-star, Beyonce Knowles, had a much different experience with "Dreamgirls" as she was determined to drop 20 lbs for the role. Though the singer has plenty of curves, she certainly didn't need to lose any weight. "The director (Bill Condon) actually kept telling me to 'eat, eat, eat' for continuity, but I really wanted to go all the way," Beyonce told People Magazine. "I was inspired by Tom Hanks. He did it all the way (in Castaway), so I said, I can do it all the way!"

However, Beyonce isn't the only skinny girl dedicated to being healthier. Supermodel Heidi Klum lost her baby weight, going from 165 to 135 lbs, by sticking to whole grains, greens, egg white omelettes, and protein shakes while pregnant. While this might sound unappetizing to some, it often takes this kind of effort to look good. Luckily, you don't have to be famous for it to work for you.

"The main idea is being consistent during your workout and actually working during your workout. You've got to be willing to do that work. That's what my celebrities do. It's not like they come in my gym and we sit in my office and take a pill and drink some elixir. They get after it," Gunnar tells us. "If the average person can embrace the concept of having to do the work to achieve the physique, there's nobody out there who won't see some kind of result."

After all, as other pound shedding celebrities like Star Jones, Peter Jackson, Ethan Suplee, Carnie Wilson, and Al Roker can attest, why be famous if you can't enjoy the benefits of being healthy? "Who wants to work so hard for money and autonomy and then get to an age where you can't use it the way you want to because you're physically not up to the task?" asks Gunnar. "When you have your health, you have everything."