Credit: Jeffrey Mayer/; Gabriel Olsen/FilmMagic

Tipping the scales at 263 pounds, model turned Celebrity Rehab tech Jennifer Gimenez knew it was time to change when she couldn't fit into her favorite frock.

"A fabulous dress I'd had for years didn't fit," the 34-year-old single star tells Us Weekly. "I finally looked in the mirror, saw an obese girl and just cried."

Shocked into shrinking, Gimenez took part in a cleanse for 21 days to kickstart her weight loss -- but the results didn't last long. "I lost six pounds, and within two weeks gained 18 back," she explains.

Once she met with a nutritionist, Gimenez says she learned the right way to eat, and eliminated oil and sugar from her diet.

Coupled with exercise, Gimenez's new eating plan helped her shed 50 pounds in the first four months of her weight loss journey. In the weeks since, she's shed an average of one or two pounds per week.

Says Gimenez: "Do it wrong, it comes back. Trust me."