Can an employer decide not to hire you if you are a smoker or you are obese?

Can an employer decide not to hire you if you are a smoker or you are obese?
 i think that it depends on the job occupation because if the job has a rule against smoking than they can decide not to hire you. Because maybe at a doctors office they can't hire you because there is no smoking at a doctors office. It depends..

And if they don't hire you if you are obese then maybe it also depends on the job occupation cause if you are a yoga instructor or an instructor of some sort they don't want someone who is obese to be training others because maybe they want someone the trainees can look up to. But they can't just not hire you because you are obese because maybe you are a very good hardworking person.