What is the difference between these sentences?
Tell me, doctor, shall I lose weight?
Tell me, doctor, will I lose weight?
What is the difference between these sentences?
Tell me, doctor, shall I lose weight?
Tell me, doctor, will I lose weight?
There is no difference in meaning between the two sentences. If you want to be pedantic you can follow the old rule:
Well, in traditional British grammar, the rule is that will should only be used with second and third person pronouns (you; he, she, it, they). With first person pronouns (I and we), the 'correct' verb to talk about the future is shall.
In everyday conversation the two modal verbs, "will" and "shall" are used interchangeably. I doubt that one in ten native English speakers would know the rule.