Federal health advisers are meeting to review a group of controversial chemicals called peptides. The unapproved injections have become a popular wellness trend, promoted by influencers and celebrities for building muscle, healing injuries and other uses. The two-day meeting underway Thursday comes at the direction of Health Secretary Robert F. Kennedy Jr., who has described himself as a “big fan” of peptides. Some of the outside experts invited by the FDA have financial ties to the peptide industry, including several doctors who run clinics that offer the injections. The panel will vote on whether the FDA should allow seven of the most popular peptides to be produced by pharmacies.