Any graduate degree will help some. And if you don't have GPA problems, an MPH or MS in Nutrition (like the other posters listed), or any other non-science degree might be okay.
However ... if you have a weak undergraduate GPA or a low MCAT, you need to demonstate that you can do well in pure science courses. Because of this, a masters degree in biology, chemistry, or physics would be the best way to go.
Alternatively, you can do a post-bacc program. But if you are trying to redeem yourself academically, stick to biology, chemistry, and physics.