What to Eat and Not to Eat Before a Marathon: The Ultimate Fueling Guide
                                
                                
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                                    4 min read                                
                            
                                According to sports dietitians, up to 70% of a runner's calories in the days leading up to a race should come from carbohydrates to maximize energy stores. Learning what to eat and not to eat before a marathon is critical for peak performance and avoiding gastrointestinal issues.