The magic formula to losing weight? Eating less and exercising more. But how much exercise will translate into weight loss?

The current guidelines from the Centers for Disease Control and Prevention and the American College of Sports Medicine recommend 30 minutes or more of moderate-intensity physical activity on most -- and preferably all -- days of the week. That amount is enough for most people, and it’s a good starting point for overall fitness. But for weight loss, you need to burn a minimum of about 200 calories a day at least three days a week.

How do you define "moderately intense"? You could count your heartbeats to determine how intensely your body's working, but the American Heart Association’s conversational-pace rule is the easiest way to determine whether or not you’re exercising at the proper intensity. If you can walk and talk at the same time, you’re probably walking at the right pace. But if you can walk and sing, you’re probably not working hard enough. And if you get out of breath quickly, you’re probably working too hard -- especially if you have to stop and catch your breath.

How frequently and intensely you exercise, as well as how long you work out, determines how much fat you burn. But don’t overdo it. To burn fat, you need oxygen; get your heart and lungs pumping with aerobic activities.

If you exercise so vigorously that you can’t breathe, however, your workout is anaerobic (not using oxygen), which means that you’re using carbohydrates and possibly protein (from your lean muscle) for energy, not fat. So if you want to lose weight, focus on losing fat by not overdoing the intensity of your workout.