The singer, 21, showed off her trim physique in a playful bikini photo on Twitter
Of her weight loss, the season 6 American Idol
winner tells PEOPLE: "It was just a shift in my thinking. Instead of talking about being more active, I just got up and did it."
"There's no secret," she adds. "Anybody can do it."
Describing her polka dot orange and blue two-piece, she posted online, "I don't know why but my bathing suit reminds me of fruity pebbles."
Want to get her look? The savvy shopper shares that her "top is from Target & bottoms from Old Navy!"
But her slender look isn't keeping Sparks from indulging in sweets every now and then. "Love that I can now bake my coconut rum raisin cupcakes because I can legally buy the rum! Ha!" she Tweets.