Jenny Craig, now known as Jenny, has been using celebrities to advertise it's program for a number of years now. Mariah Carey is the latest who shed over 30 pounds after giving birth to twins. While I think some parts of the Jenny program are good in that you are provided with an individual counselor, unlike the group meetings of Weight Watchers, it's still a food based program. Weight Watchers claims the Jenny advertising is deceptive (ABC article here) and I tend to agree with them. Neither Mariah Carey nor Valerie Bertinelli lost weight by eating Jenny Craig food alone. No one can get a body that toned without vigorous exercise and/or surgery.
So unless Jenny Craig is now providing a personal trainer included in their program they might take the credit for the weight loss, but not for the toned bodies of their skinny celebrities.
Valerie Bertinelli's weight loss plan here.