There's a temptation, when in the midst of serious training, to think you have to adhere to some inanely strict new diet — that you have to learn a whole new way of eating to pair with your new life as a capital-R Runner. But no, the key is to keep it simple. "Your body knows what it needs, and really it's just a balanced diet," says Honerkamp. "If you eat a balanced diet, all the nutrients you need are there. It's just eating smart — not having a heavy meal after 6 or 7 o'clock, eating breakfast, which a lot of us skip. You know, having yogurt and some berries versus skipping that." And don't fall prey to the opposite, either. "One of the things for new runners is that they think they can eat whatever they want," says Honerkamp. It's like, you're running five miles three days a week — it's great, but it doesn't mean you can eat a Big Mac every day."