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 get their body weight down to the point where they look like a professional athlete in order to derive any health benefits," says study co-author David Thompson, Ph.D., a health economist at Policy Analysis in Brookline, MA. "That's just not true, and it tends to be self-defeating."

Janet Helm, a St. Louis dietitian and spokeswoman for the American Dietetic Association, says one of the main challenges dieters face is staying motivated. Making your goal more moderate can help combat burnout. "If you can focus on losing each at a time—and recognize that there are benefits for every step you take—it can be more encouraging," says Helm.

If you're currently at a healthy weight, Thomson suggests that you focus on what's kept you there, a healthy diet and a normal exercise routine. "If someone at a healthy weight tried to lose 10 percent of their body weight they could become vitamin and mineral deficient or develop an eating disorder."