Weight loss secret: How Jordin Sparks Lost 50 Pounds

"American Idol" champ Jordin Sparks is showing off her new svelte physique on the cover of Shape magazine's August issue.

Sparks, 22, has shed 50 pounds and is four sizes smaller than she was when she first appeared on "American Idol" in 2007.

"I just wanted to be healthy," Jordin told Shape. "It was just before my 21st birthday. I had walking pneumonia, couldn't breathe and felt totally fatigued. I remember thinking, 'I'm in my prime. I should be happy and fit.' That was the moment I decided that changes needed to be made."

After she found her motivation, it was time to get to work -- which Sparks admits was was pretty daunting. "I knew I had a long road ahead of me," she revealed. "I was barely working out, and my diet was a mess. I had to address when, what, and how much I was eating."

She started exercising some major portion control and began by walking around her neighborhood until she felt confident enough to take up hiking. Since then, Sparks has started hitting the gym and taking Zumba classes to dance her way slim.

In addition to intense cardio sculpting sessions, Sparks, who had been dating fellow singer Jason Derulo since last August, had to makeover her diet as well. Sparks said eating smaller portions and choosing leaner foods contributed to her ability to shed the pounds.