Patty, let's just say that, as a former 320 lb. person, well, in some ways I am about as opposite from you as can be (and in some ways, very similar).
Just remember that running burns about 100 calories/mile; hence, in my case, there is really a minimal effect on my eating (perhaps 6-7 pieces of fruit a day extra?).
Also, it is very important to make sure that every run has a training purpose and to have some strict upper bounds on milage; it is all-too-easy to fall into the trap of running miles "just to burn calories" when one should be recovering.
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