Confessions of Two Ex-Fat Actresses

08/09/2007 at 12:00 PM EDT

"Is that really me? Did you stretch me somehow?" Valerie Bertinelli stares at the image of herself on a photographer's monitor in disbelief. He tells her no, he hasn't used any computer tricks; rather, after losing 30 lbs. in just over four months as a Jenny Craig spokeswoman, she really is that slim. Hearing that, Bertinelli, 47, tears up a bit. "I want to get to the size I was when [my son] Wolfie was in kindergarten 10 years ago," says Bertinelli, who split with hubby Eddie Van Halen in 2001. (For the past three years she has been dating Tom Vitale, 46, a financial planner.) "I know I can do that. I hope!" Cheering her along every step of the way? None other than fellow Jenny Craig pitchwoman Kirstie Alley, 56, who says she has kept off the 75 lbs. she dropped on the plan. As stars now known as much for the fluctuations of their scales as for career highs like One Day at a Time and Cheers, Bertinelli and Alley convened in L.A. for a frank conversation with PEOPLE's Maureen Harrington about what it feels like to be big – literally big – in Hollywood.

How did you two meet?
Alley: Our kids go to the same school. When I first saw her, I was like, "Oh, she's famous." But then I had this reaction: "I'm fat. I don't want to talk much."
Bertinelli: And that was me, too! It was like, "I don't want anyone to see me. I'm fat."
Alley: It's worse when you run into famous people, because you've lived a public life of skinny, and here you are at your child's school looking awful. That was my biggest disgrace.
Bertinelli: You just don't want people to see what you look like, because you can hear their brains going.
Alley: You don't want them to see what you've become.
Bertinelli: What always got me was someone would come up to me and say, "I think you've put on a few pounds." Really? Because I don't own a mirror? I know – believe me!
Alley: And thank you for telling me.
Bertinelli: Like that's going to help!
Alley: You have so many people "helping you." They're not helping you. They're invalidating you.
Bertinelli: That's one of the first things Kirstie said to me when we started this journey. She said it's going to be about much more than just losing weight. She was absolutely right.