Not only did Jennifer Lopez shed 50 pounds after giving birth to her twins, Max and Emme, in February 2008 - but the 40-year-old mom has kept the weight off and looks hotter than ever! Granted, staying in shape hasn't been an easy feat. "I had to work really hard," Jennifer confesses. But luckily, the sweat and suffering has all been worth it for the singer and actress. "She isn't afraid to push herself in the gym," her trainer, Gunnar Peterson, tells In Touch. "She's not somebody who blows it off because she's working 18-hour days on the set. She finds a way to get back in, even if it means exercising really late at night." Peterson tells In Touch that Jennifer exercises for at least one hour, anywhere from two to six days a week. "After a 10-minute warm-up, we do a series of strength and resistance moves, coupled with high-intensity cardio intervals and some flexibility work." Even though she's serious about training, she's careful not to lose her curves. "I do weights and cardio, but I try to take a soft, feminine approach," Jennifer has said. As far as her diet, J. Lo has been using the meal delivery service Freshology (freshology.com) since October 2008. She sticks to about 1,200 to 1,400 calories a day, and eats lean proteins, fruits, vegetables, good fats and lowglycemic carbs. "She stays ready so she doesn't ever have to get ready," Peterson tells In Touch. "She just keeps her foot on the pedal."

For more of J. Lo's weight loss secrets, check out this week's issue of In Touch, on newsstands now!