By Lisa Baertlein and Chris Prentice LOS ANGELES/NEW YORK (Reuters) – The biggest overhaul of U.S. food nutrition labels in more than two decades is likely to help improve the diets of the most health-conscious consumers, but others may need more convincing. Public health advocates welcomed the new rules but said some of the groups most at risk for obesity and diet-related illness may not change habits without other measures to discourage sugar consumption, such as taxes on sugar and food advertising warning labels. The U.S. Food and Drug Administration on Friday announced new Nutrition Facts packaged food label rules that include disclosure of how much sugar is added to thousands of processed foods ranging from soda to spaghetti sauce.