Both nutrition and health are very competitive niches. They are also prone to spamming and you have to be careful to stay away from certain spam categories. You'll be up against sites written by the American Diabetes Association in Diabetes, for example. Just about every health category will have many of those. I think the only way to succeed in it, is if you have a very unique perspective and lots of very unique content to share.
I'd say go for it, too! If these are topics you're comfortable with, writing about them should be a breeze. Besides, I think that a lot of people are interested reading about health and nutrition, so capturing audiences should be easy