Final answer:
Among the options given, surgery is often the single most effective medically proven method for treating various medical conditions such as obesity, isolated solid cancers, irreversible contraception through sterilization, and severe cases where other treatments are inadequate.
Step-by-step explanation:
The question is asking which method is the only medically proven one out of the options given: surgery, medication, time, and therapy. In the context of various medical conditions and treatments discussed, surgery is often the single most effective or definitive method. For example, bariatric surgery is recommended as the most effective medical treatment for obesity when other methods like diet, exercise, and medication do not suffice.
Similarly, in the treatment of isolated solid cancers, surgery that removes the tumor mass and sometimes the local lymph nodes can cure localized cancer or prolong survival when it's not entirely localized. Additionally, sterilization, a surgical procedure for contraception, is considered highly effective and usually irreversible. Lastly, other medical conditions may also warrant surgical interventions when less invasive treatments fail to yield expected outcomes or in severe cases.