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ABC News’ Andrea Canning and Amanda Keegan report:

Kelly Preston cheered on her best friend, Kirstie Alley, when she cha-cha’d way to the “Dancing With the Stars” finals earlier this year in twelfth season of the hit ABC show.

Today, Alley is down 100 pounds, and she has said it was hard work.

Now Preston has revealed that she looked to her best friend’s weight-loss secrets to lose the pounds she gained when she was pregnant with son Benjamin, who was born a year ago.

“I lost 39 pounds, have more energy than I had 20 years ago – and I feel amazing, I’m going to be turning 50 next year … Hey, 50 is the new 30,” Preston said in an interview with People magazine.

Michelle Tan, a senior editor at People, told “GMA” that Preston “really is a poster child for somebody who is going to be forever young … she also started a new chapter in her life she’s happier than ever with her new baby.”

Preston said she’s below her pre-pregnancy weight thanks to “Organic Liaison,” Alley’s own organic supplement system. Preston is now the spokesperson for the company.

“It’s the first USDA-approved organic weight-loss program and essentially what it is, is you drink a supplement throughout the day and it helps curve your cravings and boost your energy,” Tan said.

So how do so many other celebrity moms lose the weight and make it look so easy?

Superstar singer Mariah Carey told “GMA”‘s Lara Spencer that she owes her better-than-ever body to Jenny Craig.

Carey gave birth to twins in April. She initially lost 40 pounds of water weight after she gave birth. She lost 30 pounds afterward, through diet and exercise.

Model Miranda Kerr walked in the annual Victoria’s Secret fashion show last night, but a year ago she was 40 pounds heavier when she was pregnant with son, Flynn. She lost it through yoga and Pilates.

Padma Lakshmi, the host of “Top Chef,” turned to vigorous exercise after her daughter, Krishna, was born. She ran up 70 flights of stairs every day, lifted weights and boxed.

Supermodel Gisele Bundchen said she bounced back by doing the hard work before her son, Benjamin, was born. Her pre-birth routine included yoga three times a week, and kung fu — up to two weeks before she gave birth.

“Whether you’re a celebrity or you’re a mom … everybody relates to that idea of after having a baby, really wanting to get your body back, and so everybody is really looking for inspiration,” Tan said.