I have an MD/MPH with a biostatistics concentration. Having a stats background seemed to be a hot topic on the trail, and allows you to speak intelligently about research. In addition, I had the opportunity to do all sorts of ortho research during my MPH year (which is a bit of a joke compared to med school). It did look a little suspect to smaller programs, but to any place academic it is nothing but a plus (provided you do something like stats or epi) if you do something fluffy like health education, it may be suspect. Like most anything else on the trail, you have to make sure you have the right spin.
In addition, since starting residency, the stats background has helped me get into some projects, and has boosted me into other research situations that can only help in the future. Even should you decide to can research all together when you finish, it will still help you critically evaluate the literature. Really a no lose situation (particularly if you are young, and even more particularly if your med school is picking up the tab like mine was)