Will a Nutrition BS degree be more useful as an Endocrinologist or a Gastroenterologist?

... and why?

.....I'm aware that I have to attend medical school. I'm looking for a second major. I'm majoring in Biochemistry and I'm think about adding the Nutrition major as well.

it wont make much difference at all. It wont be given much weight at all for med school, residency or fellowship applications. Major and minor in what you want right now. Your decision regarding endo and GI are far, far away and should have no bearing on the decisions you make today regarding your education. If I were you, I honestly would just concentrate on the major and not bother with a second major. It will only add more stress to your life and not contribute much to your med school admission. That is where the focus should be now, just getting into med school Concentrate on getting into the best med school you can and apply your energy to something else that will help you there, such as research or volunteer work.

the Endo needs you as they deal with diabetics all day long