Katy Perry, 25
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When she's on tour, the Grammy-nominated singer always packs her jump rope for a quick but intense calorie-blasting workout, and she sticks to an out-of-sight, out-of-mind diet, saying she doesn't allow chips or fried foods backstage, because if she sees them, she'll eat them!
Lady Gaga, 24
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Celebrity trainer Harley Pasternak keeps the singer sleek and sexy with his 5-Factor Fitness program. She grazes on five small meals a day and works out five times a week, doing cardio, weight lifting with dumbbells, and crunches.
Jennifer Hudson, 28
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The Grammy and Oscar winner is on a losing streak these days, with the help of Weight Watchers. She focuses on portion control and healthy food choices—and keeps a daily food journal. To firm up her new figure, five days a week she does a 50-minute circuit routine of running on the treadmill, lunges, shoulder presses, and ab work.
Lea Michele, 23
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When she's not putting in 16-hour days singing and dancing on the set of Glee, this spunky Broadway babe likes to go for long hikes at L.A.'s Runyon Canyon Park. To fuel all that activity, she recently switched from a vegan to a macrobiotic diet by occasionally adding fish to her meals.
Gwen Stefani, 40
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Known for her fit physique, the No Doubt singer typically takes daily jogs or hikes in her L.A. neighborhood, then does hard-core biceps and triceps training and crunches with a medicine ball. Her healthy meal plan consists of lean protein, like chicken; organic veggies, including carrots and cucumbers; and seasonal fruit, such as strawberries and pears.
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This month's cover girl keeps fit by jumping on the treadmill for at least 30 minutes three times a week and by doing seriously steady ab work. She also depends on a healthy diet to stay slim: Her favorite foods include salmon; whole grains like oatmeal; kale; and dandelion greens.
Get Jewel's stay-fit rules and her whole workout here.
Katharine McPhee, 26
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The two-time Shape cover model stays toned with a high-intensity workout that includes at least 30 minutes of running on the treadmill, squats, and push-ups five days a week. She prefers simple meals: whole-wheat toast with marmalade for breakfast, a tuna sandwich for lunch, and grilled fish with veggies for dinner.
Carrie Underwood, 27
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She's been a vegetarian since she was 13, but Carrie struggled with her weight until a few years ago, when she started keeping a food journal. More recently, she's cut back on dining out in restaurants whenever possible to avoid high-calorie dishes. To keep her body toned, she swims or does kickboxing several days a week.
Sheryl Crow, 48
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Sheryl, who's been on Shape's cover twice, loves outdoor activities like tennis and surfing, but to maintain her weight and flexibility, she does an hour on the treadmill and Pilates five days a week. As for this breast cancer survivor's diet, it's all about omega-3s, with staples like salmon, brightly colored vegetables, and walnuts.
Mel B, 35
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The host of Oxygen's Dance Your Ass Off keeps her own booty beautiful by following three simple rules: Do 30 minutes of aerobics every day (check out her Totally Fit DVD); eat a healthy, balanced diet filled with lean protein, like salmon, and lots of salad; and allow yourself one cheat day per week.