Easy stroll won't bring weight loss

About 10 years ago doctors noted that most Americans weren't getting any exercise at all. They encouraged people to walk briskly for a minimum of half an hour a day. They wanted to get sedentary people off the sofa.

Many people did that light exercise. Their health benefited by a decrease in heart disease, premature death, stroke, type 2 diabetes, osteoporosis, and certain cancers. But their waistlines stayed the same or grew.

The National Academy of Sciences' Institute of Medicine calls for 60 minutes or more a day of activity to prevent weight gain and to get more benefits. About 120 million people in the U.S. are overweight or obese.

Doctors at Harvard Medical School say people have to stop kidding themselves about what it takes to control weight. It takes intensity, and it takes time. For half of the 60 minutes. You need to break a sweat and breathe heavily. The rest can be 10-minute periods of moderate activity.

Obesity experts at the University of Colorado Health Sciences Center in Denver say that if everyone did 30 minutes of activity a day, it would be huge for public health. But it wouldn't make them lose weight. (Only one in three people even do the 30 minutes of moderate exercise.)

If you are meeting the 30-minute guideline and your weight is inching up, do more. Some people have success when they do 45 to 60 minutes of moderate exercise.