In the February issue of Cosmopolitan (excerpted by Radar Online), the 30-year-old "Catch My Breath” singer opens up about her 30-pound weight loss in 2012. "I think that happens when you fall in love or date someone,” Clarkson explains. "If I’m going to be messing around, I gotta look good.”Clarkson promises she didn’t try a "fad diet” to get in better shape."I was working with a trainer, and she said, ‘You’d be amazed the amount of weight you can drop by halving your portions. I know it sounds crazy, but do it for two weeks and watch what happens.’ I just cut back my portions, I stopped eating late at night, and I work out a little more than I used to, and I literally dropped 18 pounds in a month,” the American Idol winner reveals. "I think it happens when you get really busy. But when I’m on my off-time -- girl, those 18 might come back!”Us Weekly