From gluten-free to all-Paleo, GMOs to grass-fed beef, our newsfeeds abound with nutrition advice. Whether sensational headlines from the latest study or anecdotes from celebrities and food bloggers, we're bombarded with "superfoods" and "best ever" diets promising to help us lose weight, fight disease, and live longer. At the same time, we live in an over-crowded food environment that makes it…