The singer posted a letter to her fans on Monday blasting false reports regarding how she shed the pounds.
"Though I NEVER care what the tabloids have to say about me … I wanted to address this certain story they are running this week and set the record straight. I DID NOT have surgery to lose weight. That is ridiculous," she wrote.
Added the star: "I lost my weight the healthy and good old fashioned way. Watching what I eat and working out with my trainer Bill Crutchfield."
Lambert, who dropped a dress size, also admits in the letter that she doesn't know how many pounds she's lost.
"It's not about a scale. It's about how you feel and how your jeans fit. And on November 10th when I turned 30, my skinny jeans were finally baggy! Mission accomplished! So for anyone who is tempted to read the "Trash Talk" please don't," she said. "I am proud to be a normal size girl and I want to encourage everyone to be confident at any size."
The singer recently told PEOPLE the key to her successful weight loss is portion control and her workouts with Crutchfield.
"We do cardio, a lot of circuit training. We do things with my body weight, like lunges. A lot of stuff with [resistance] bands," she said. "The stuff nobody loves, but it works!"