4 MAJOR Slimdowns—How These Celebs Lost Weight!

Melissa McCarthy, 44, admits she piled on the pounds during her two pregnancies (in 2007 and 2010). "If I wanted a piece of toast, I'd have one," she said. But gradually she embraced a low-carb, high-protein diet and exercise plan including Pilates and tennis--with smashing results. "She started with baby steps, and I like that," said Richard Giorla, a celebrity trainer and founder of Cardio Barre. "Tennis burns maximum calories, and Pilates gives stretch and core strength." See what she looks like 50 pounds lighter in the next photo!

What you can do: High-protein foods--egg whites, tuna or hummus, eaten with veggies--"will kick-start your nutrition," says Richard, who also advises splitting a meal when dining out and using small plates at home. For Pilates-inspired toning moves, he favors plié squats and bridges ("100 reps--until it burns!").

Adam Sandler, 48, has shed his spare time—but not the way you might think. "You don't get abs from doing a lot of abdominal [exercises]," says celebrity trainer Duffy Gaver, who's worked with Adam in the past, sending him on six-to eight-mile runs and doing weight training. "What strips that layer of fat off your body is eating right and burning calories." Adam's cardio workout of choice lately? Pickup basketball! See what he looks like 10 pounds lighter in the next photo!

What you can do: "Make the bulk of your food vegetables and lean protein," says Duffy. "Starting your day with a Frappuccino isn't going to work.  Stop eating late, and focus on portion control--wating more slowly and chewing your food more.  You'll feel satiated longer." 

Chris Pratt has remade himself into an action star—and an Ironman triathlete! To transform from his former dought, 300-pound self, the 26-year-old actor acted a three-level workout plan with Duffy: getting disciplined with diet and putting on muscle with old-school body-building; metabolic work like sprints and pull-ups; and finally longer, nonstop conditioning sessions using lighter weights. See what he looks like 60 pounds lighter (in six months!) in the next photo!

What you can do: Seeing a nutritionist along with a trainer, as Chris did, "helps because they'll back each other up," Duffy says. "If I say you should eat chicken, broccoli and brown rice, and the nutritionist refines your diet a bit more but says the same, it reinforces what you're learning."

Never shy about showing off her shape, Lena Dunham's now happier than ever to do so! The Girls creator, 29, is doing the Tracy Anderson Method workout (a la Gwyneth Paltrow), and using meal-delivery service Sakar Life, which focuses on plant-based protein and fiber and "doesn't count calories or carbs," says founder Danielle DuBois. A typical day's dishes include a stone-fruit-and-kale salad and a bowl of vegetables, beans and rice with avocado dressing. See what she looks like 25 pounds lighter in the next photo!