Middle-aged female dieters, take heart. It's not too late to lose a significant amount of weight if you make the right changes and stick with them, according to research presented at the annual meeting of the Obesity Society.

Women who are committed to make changes can lose 20 pounds, says Karen Foster-Schubert of the Fred Hutchinson Cancer Research Center in Seattle.

They need to write down what they eat, prepare food at home instead of eating out and make weight loss a priority, says lead investigator Anne McTiernan, director of the Prevention Center at Fred Hutchinson.

Researchers recruited 439 overweight or obese postmenopausal sedentary women, average age 57, average weight 185. They were assigned to one of four groups: diet only, exercise only, diet and exercise, or no lifestyle changes.

Participants in the diet-only group worked with registered dietitians weekly for six months, then monthly for six months to change their eating habits. They learned how to keep food records, shop for healthful foods and prepare lower-calorie dishes.

Those in the exercise-only group were encouraged to exercise moderately, working up to 45 minutes of aerobic exercise five days a week. Three of those weekly sessions were supervised by exercise physiologists.

The third group was given both the diet and exercise components of the plan. The fourth group was given no diet or exercise guidance. After a year, the diet-and-exercise group had lost about 21 pounds; the diet-only group 18 pounds; and the exercise-only group almost 5 pounds. The control group did not lose a significant amount.

Although men were not included in the study, they too might lose weight if they made such changes, Foster-Schubert says.