Federal health officials are moving ahead with plans to broaden access to a class of unproven injectable drugs called peptides. According to a government online posting Thursday, the Department of Health and Human Services submitted a plan to the White House that would allow temporary access to some of the products. Peptides are essentially unapproved, injectable drugs that have become popular among people looking to build muscle, look younger or boost energy. Health Secretary Robert F. Kennedy Jr. has described himself as “a big fan” of peptides and directed the Food and Drug Administration to consider loosening restrictions on their use.