Good question, I think about this all the time.
What got me interested in nutrition (and the environment/animals) was actually the documentary Food, Inc. Oddly enough, it hadn’t occurred to me until then that what I ate was even connected to my health. After watching that, I watched Food Matters. That was the turning point. I ordered books like The China Study and others on raw veganism, and after reading them, decided that I would begin my own health journey. I was vegetarian for 2 months before I transitioned to a vegan diet. Before I knew it, I no longer found my favorite junk foods appealing. (I guess knowing what was in them had something to do with that!)
A lot of books and documentaries later, I also began to consider what products I put on by body. This led me to donate all of my beauty and skin products to a program that recycles cosmetics, as well as to ditch shampoo and conditioner for no-poo.
And here I am.. Blogging and eating vegetables!