From the Mayo Clinic: "researchers found that healthy young people who put on as little as 9 pounds of fat, specifically in the abdomen, are at risk for developing endothelial cell dysfunction. Endothelial cells line the blood vessels and control the ability of the vessels to expand and contract. ... [researchers] recruited 43 healthy Mayo Clinic volunteers with a mean age of 29 years. They were tested for endothelial dysfunction by measuring the blood flow through their arm arteries. The volunteers were assigned to either gain weight or maintain their weight for eight weeks, and their blood flow was tested. The weight-gainers then lost the weight and were tested again. ... Endothelial dysfunction has long been associated with an increased risk for coronary artery disease and cardiovascular events. Gaining a few pounds in college, on a cruise, or over the holidays is considered harmless, but it can have cardiovascular implications, especially if the weight is gained in the abdomen. ... Among those who gained weight in their abdomens (known as visceral fat), even though their blood pressure remained healthy, researchers found that the regulation of blood flow through their arm arteries was impaired due to endothelial dysfunction. Once the volunteers lost the weight, the blood flow recovered. Blood flow regulation was unchanged in the weight-maintainers and was less affected among those who gained weight evenly throughout their bodies."