People who were overweight and then lost weight, especially belly fat, can improve blood vessel function no matter what diet they chose, U.S. researchers say. Lead investigator Kerry J. Stewart, a professor of medicine at The Johns Hopkins University School of Medicine in Baltimore, who is also director of clinical and research exercise physiology at The Johns Hopkins Heart and Vascular Institute, studied 60 men and women who weighed an average of 215 pounds at the start of the program. Being overweight increases the risk of cardiovascular disease, especially if the fat is accumulated in the belly above the waist, Stewart said. Half of the participants went on a low-carb diet while the others followed a low-fat diet. All took part in moderate exercise and their diets provided a similar amount of calories each day. In the six-month weight-loss study, the researchers found the more belly fat the participants lost, the better their arteries were able to expand when needed, allowing more blood to flow more freely. The researchers found participants in the study who were on a low-carb diet lost about 10 pounds more, on average, than those who were on a low-fat diet. The findings were presented at the American Heart Association scientific meeting in San Diego.