Precious heft! GABOUREY SIDIBE tells MO’NIQUE fat chance she’ll lose weight! 

SLIMMED-down Mo’Nique is on a quest to help everyone lose weight, and she’s starting with her plus-size “Precious” co-star Gabourey Sidibe. But Gabby – who reportedly weighs as much as 350 pounds – told the Oscar winner: “Thanks, but no thanks.”

“Mo’Nique’s weight loss journey has been slow but steady, and the results have completely changed her outlook on life,” a source told The ENQUIRER.

“She looks and feels amazing and that’s why she reached out to Gabby. “Mo’Nique knows how hard it is to be heavy, and since she and Gabby have discussed their battle of the bulge, she thought she could reach out.

“Unfortunately, Gabby politely declined.”

The 45-year-old former star of “The Parkers,” who’s been documenting her weight loss on Twitter for the past three years, has dropped from a high of 300 pounds to less than 220.

As The ENQUIRER previously reported former “View” co-host Star Jones, who shed 160 pounds through gastric bypass surgery, questioned whether Mo’Nique was being honest about her weight-loss methods.

But Mo’Nique brushed off the comments, accusing Star of being jealous for not being able to handle her own weight issues without resorting to surgery.

Meanwhile, Mo’Nique was so anxious to share her success with 30-year-old Gabby that she offered to perform dual workouts with her over the Internet video phone service Skype.

But Gabby, who just wrapped up four seasons on Showtime’s “The Big C,” wasn’t moved.

“Gabby loves Mo’Nique and thinks it’s great that she’s losing weight, but she’s just not interested in dieting at this point in her life,” added the source. “She says she knows she has to do something, but she’ll do it in her own time and on her own terms.”