If your doctor has advised you to lose a relatively large amount of weight (25 pounds or more), don't get hung up on that number. According to new research, losing just 10 percent of your body weight can be as beneficial to your health as dropping 40 or 50 pounds. The study, published in the October issue of the American Journal of Public Health, reports that overweight people who lose and keep off 10 percent of their body weight greatly increase their life expectancy and reduce their risk of coronary heart disease, hypertension, stroke and diabetes. "Most people think they need…