"You can achieve weight loss just by reducing calorie intake, but the challenging thing is to keep it off for long periods of time," said Dr. J. Esteban Varela, associate professor of surgery at Washington University School of Medicine in St. Louis. "It's going to be difficult to stick to the plan in the long term, and she will have to restrict her portions for life."
They stress that in order to maintain weight loss, the sisters -- especially Muir, since she isn't physically restricted from overeating -- must make gradual lifestyle changes, including exercise and remaining mindful of portion sizes.
"A good guideline is to make one change every two to four weeks, but make them forever changes," said Ayoob.
Muir said she's started going to the gym regularly, and has learned a number of strategies for reducing her portions.
"I swapped my plate for a smaller plate. I put my portions on there. I was thinking I was eating a lot because I saw my plate full."
She also said she chews her food very thoroughly, which makes her feel full more quickly.
Weight loss specialists disagree about whether the sisters' story provides evidence that weight loss surgery isn't always necessary.
"The sister didn't need the surgery," said Wolper. "If they're similar in terms of their motivation and their can-do attitude, it's clear they both could have done it."
"If you can achieve this kind of weight loss without surgery, chances are that's not going to be successful long-term," said Varela. "Surgery helps bring about an attitude change toward food."
The experts say they are impressed by Muir's willpower and determination, and Muir's family told her the same thing.
She says she now enjoys shopping for new clothes and playing with her grandson. She wants to tell others who want to lose weight not to give up, believe in themselves and find a "diet buddy" to help.
"If I can do it, anyone can do it," she said.