It is true that a bio major is more "traditional" for pre meds, and for that reason, you may be asked to explain your change of major. Don't let that bother you though. If someone "harshly questions" you, their real intention is to see how you respond. As long as you have a sincere reason for wanting to go MD and can explain your interest in nutrition (and its relationship to medicine as oNichole said), then you should have no prob with this.
Personally I think a bio major would help you more in the long run, and I would stick to bio as a major, but that's just me.