When I told friends I was eating nothing but fast food for a week, most immediately thought of the (in)famous Morgan Spurlock documentary "Super Size Me."

No, I would respond. I'm eating healthy.

As fast-food chains increasingly try to appeal to health-conscious Americans, supposedly nutritious items are popping up on menus more and more.

From KFC's grilled chicken to McDonald's (shockingly caloric) kale salad, massive restaurant chains want to signal to customers that nutrition and fast food can go hand in hand.

If these chains want to compete with the new wave of healthier fast-casual alternatives, they're going to have to prove they can become daily go-tos for nutrition-savvy millennials.

So I decided to see for myself how the chains, and my stomach, held up after a week of eating only at fast-food restaurants.