Allen, once a svelte dancer on the hit show "Fame," which she also choreographed, today finds herself buried in a hectic schedule and fighting her own battle of the bulge.
"I actually have lost 20 pounds," Allen said. "Twenty pounds, but she has lost, what, 38? Oh, no, no, no! I'm sorry. I have to keep it up. I'm going to have to catch her now."
Allen says after dropping the 20 pounds she feels "so cute."
The sisters, who say they are best friends, are teaming up on a new version of Tennessee Williams' classic play "Cat on a Hot Tin Roof," with Allen directing her sister, who doesn't look the part of Big Mama quite as much as she did during the last run.
"A person can be big, because of spirit," Rashad said. "A person can be big because of their position in the family, the hierarchy in the family. That role has been played by women who are quite thin."
Many stars celebrate their new svelte shapes with bikini cover shots, but Rashad says fans shouldn't hold their breath.
"I'm not that kind of girl," she said, laughing.
And Allen? She said she's past the age to wear a bikini, but a one-piece isn't out of the question.
"I have got to catch her. I am determined to catch her. And I will take the swimsuit photo. I will. Yes, I will," Allen said.
This year marks the 25th anniversary of the debut of "The Cosby Show." For many viewers, Clair Huxtable represented the first glimpse of a poised, professional black woman who was a parent first, much like the current first lady. But Rashad says she doesn't think her character laid the groundwork for first lady Michelle Obama.
"Clair was scripted," Rashad said. "Mrs. Obama is not."