I would say such a study is difficult to perform, somebody from the set of people requiring a structured system like weight watchers might be from a different s

I would say such a study is difficult to perform, somebody from the set of people requiring a structured system like weight watchers might be from a different set of people who lose weight through other approaches. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4777230/#!po=5.84416 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4777230/#!po=5.... indicates there are definitely approaches people in the US can take and have taken to reliably maintain weight loss over extended periods of time.