O You! with Fitness Expert Jim Karas

Do you spend hours sweating on the treadmill but can't seem to lose any weight? According to fitness expert Jim Karas, cardiovascular exercise is not the most effective path to weight loss. He joins up with Gayle at O, The Oprah Magazine's O You! event in Miami to talk about his new weight loss program.

Jim is the author of The Cardio-Free Diet and has worked with Gayle as her personal trainer. He says that interval-based strength training combined with a healthy, low-calorie diet is the key to weight loss. For beginners, Jim recommends 20 minutes of strength training three times a week in order to boost your body's metabolism and build lean muscle.

Contrary to popular belief, Jim says strength training will not cause women to bulk up. "You're going to get lean, you're going to get long, sexy muscles, you're going to look fantastic," he says. "Heavy weights, low repetitions, best results!"

If you're still not convinced that less cardio will yield better results, Jim says to think of strength training as smart cardio—you'll still work up a sweat and improve your heart's health, but you'll avoid all the injuries associated with cardiovascular exercises such as running. "Your heart rate is zooming up and down [during strength training], you're just not pounding it out—and while you're doing that, you're maintaining your body's lean muscle mass, which is the most important thing," he says.