You can lose weight with regular exercise. The key is to exercise long enough and hard enough so that your body burns more calories each week than you have put in your mouth.

Most people have the best success at calorie burning with moderate to intense aerobic exercise for 45 to 60 minutes at least five times per week. If your level of exercise has been none or minimal, try this 10-week startup program.

After the 10 weeks you should be ready to up the intensity and duration of your workouts using your heart rate as a guide. Here's how:

You gauge your heart rate during exercise as a percent of your maximum heart rate. Your max heart rate is 220 beats per minute minus your age in years. So an average 50-year-old would use 170 beats per minute as an initial heart-rate maximum. To qualify as moderate-intensity exercise, your heart rate should remain at 50 percent to 75 percent of your maximum for the duration of your exercise routine. Heart rates above 75 percent of maximum are considered high intensity; above 90 percent usually puts you into an anaerobic mode. A healthy, fit individual may do bursts of anaerobic activity, quickly backing off to recover in an aerobic zone.

You can measure your heart rate by feeling your pulse frequently (it's best to feel the pulse in your neck) or by wearing a heart-rate monitor (about $50 for a basic model). Many health centers have aerobic exercise machines with built-in heart-rate monitors.

Another common way to make sure that you are staying aerobic is "the talk test," which is simply the ability to talk while exercising. You may be breathing fast and hard, but if you can still carry on a conversation, you are still aerobic. If you are breathing so hard that you can't talk, you are more likely to be anaerobic. Failing the "talk test" lets you know that you may be going anaerobic.