Appealing to ethos is appealing to the credibility of the person saying something. In this case, you talk about doctors and since the advice is about health, doctors are good for giving health advice, so they gain credibility as health experts when they say something like that more than if a coal miner said it, for example.
I think the answer might be True, because generally speaking you need to state your thesis and your 3 main points anyway, in order to inform the reader the purpose of what they're about to read.
