Shortly before Miranda Lambert arrived at the Country Music Association Awards in Nashville on Nov. 6, husband Blake Shelton, 37, couldn't contain his pride. "My wife is so hot it's ridiculous," he tweeted. He wasn't kidding: When Lambert hit the red carpet, her svelte new figure set the crowd abuzz. "I didn't know until tonight that people were noticing," she told PEOPLE of her slimmed-down look. "But you want people to notice when you've worked hard and feel good. That's part of the reward. It's a great motivator."

Equally motivating were the prospects of promoting a new album in the spring and celebrating her 30th birthday on Nov. 10. "I spent my 20s on a roller coaster—my yo-yo weight, working all the time and partying," the singer explains. "I just wanted to get healthier and go into my 30s in the best shape I could be in." So, after one last "beer and Cheetos" hurrah on July 4, "I said to myself, 'It's time.' " Lambert took a personal trainer on tour. "We do cardio and a lot of circuit training," she says. "We do things that use my body weight, like lunges." She also changed her diet (see sidebar), helping her lose a dress size. "People think I lost more, but I'm 5'4", so when I lose, I lose everywhere."

At first, Shelton didn't say much. "I said to him, 'You're not encouraging me in this!' And he said, 'I have never had a problem with any way you look. You are beautiful to me at any size and every size." Still, Lambert adds, he has taken notice. "He brags on me," she says. "That makes me feel great." And despite her hard work, she insists, "I haven't given up everything!" After scooping up the CMA female vocalist award for the fourth time in a row (tying Reba McEntire's record), she was considering a fitting reward: "I might have some Cheetos tonight, just to celebrate."