Meet Mark. He’s an experienced runner preparing for the Tucson Marathon. He’s completed marathons before, but this time, he has a specific goal: achieve a personal record. Mark is consistent with his training and knows the basics of running nutrition. He’s read articles about carbohydrate intake, how much protein he should eat, understands that fueling before a run is important, and has experimented with different strategies. Despite these efforts, he continues to experience the same frustrating problem: around miles 10–12 of his longer runs, his energy starts to decline. Some days, he feels great. Other days, he struggles to maintain his pace despite feeling physically prepared for the workout. He’s putting in the training, but he doesn’t feel like he’s reaching his full potential. That’s where working with a sports dietitian comes in. Credit: Sam Siliton Step 1: Understanding the Runner, Not Just the Miles During our first appointment, we’re not