In a study published in the American Journal of Public Health, researchers determined that 15 minutes of brisk walking per day is not enough exercise to stave off obesity. Physicians from the Geneva University Hospital in Switzerland calculated that a person's weight gain is equivalent to an average of 100 extra calories consumed each day. To gauge the amount of exercise needed to burn these extra calories, researchers studied the physical activity of 3014 male and 2996 female subjects between 1997 and 2001.
Although 15 minutes of walking was not enough to burn the extra calories consumed, the investigators found that, if the subjects increased their time to 30 minutes of brisk walking or 60 minutes at a slower pace, that would be more than enough to compensate for the extra calories. The doctors are continuing to test their prediction about the amount of exercise needed to prevent obesity.