Established weight-loss companies are facing competition from upstart businesses even as they lose customers to changing tastes. Industry watchers say 2015 will be the year that many diet companies ditch celebrity endorsements, and instead focus on the weight-loss struggles of ordinary people. Those seeking to lose weight are increasingly forgoing foods labeled “diet.” Many are turning toward licensed professionals for counseling in behavior modification, a shift that some say is attributable to the Affordable Care Act, which requires most insurers to address obesity.