Sometimes, losing weight can be easier than preventing it from coming back. So, finding ways to help Americans keep off the pounds they've shed is the focus of a new study launched by the U.S. National Heart, Lung, and Blood Institute (NHLBI). The Weight Loss Maintenance Trial will be done in two phases at four sites, and it will include 1,600 men and women in the first phase and 800 in the second phase. The first phase is a five-month weight loss program and the second phase will try to help people who lose at least nine pounds during the first phase to keep that weight off for 2.5 years. The study is currently recruiting volunteers. They must be overweight or obese, aged 25 and older, and be taking medication to control high blood pressure and/or high blood cholesterol. About 60 percent of the study subjects will be women and 40 percent will be black. "Maintaining weight loss is a critical element in the struggle against overweight and obesity, which have reached epidemic proportions in the Unites States. Two out of every three adults are overweight or obese. This study could yield answers that can help many Americans lead healthier lives," NHLBI director Dr. Claude Lenfant says in a news release. Overweight/obesity is the second leading cause of preventable death in the United States. People who are overweight/obese have a greater risk of heart disease, high blood pressure, high blood cholesterol, diabetes, stroke and some cancers. About 65 percent of Americans adults -- nearly 129 million people -- are overweight or obese. The four centers taking part in the study are: Duke University; Pennington Biomedical Research Center at Louisiana State University in Baton Rouge; Kaiser Permanente Center for Health Research in Portland, Ore.; and Johns Hopkins Medical Institutions in Baltimore.