Former Surgeon General C. Everett Koop, on a new crusade to slim down the one-third of Americans believed to be overweight, kicked off his "Shape Up America!" campaign at a White House ceremony today. At his side: First Lady Hillary Rodham Clinton, with whom he joined forces on health care reform. Launch of the non-profit Koop Foundation's effort was timed to follow a report from the Institute of Medicine describing the difficulties of shedding pounds and attacking commercial weight-loss programs for causing ineffective yo-yo dieting. But outside the White House, a group of marchers criticized Koop for sending a message that overweight people could shape up easily. For his part, Koop says obesity-related conditions are the second leading cause of death in the U.S., after smoking, and that even modest weight loss can help obese people significantly improve their health.