Experts agree that a sound nutrition plan is an important part of marathon training; however, exactly what that plan should look like is often debated.
Should you be following a high-carb or high-fat diet during training?
Here's the skinny on two of the top marathon nutrition plans to help you decide which one is right for you.
The High-Carb Plan: Giving Your Body What It Wants
For decades, coaches have been telling their runners to eat a high-carb diet both during training and on race day. The reason for this is simple: glycogen is your body's preferred source of fuel and eating a high-carb diet is the best way to ensure a steady supply of glycogen. Studies from the Journal of Sports Sciences show that by keeping your gas tank full, you can put more effort into your training workouts, which should translate to better performance on race day. As a rule of thumb, aim to take in 1 gram of carbohydrate per kilogram of body weight per 10 minutes of exercise you do each day. During the marathon itself, you should aim to take in around 60-90 grams of carbohydrates per hour.
The High-Fat Plan: Stoking Your Body's Fat-Burning Fire
Runners and coaches in the high-fat camp believe that the diet helps runners prioritize fat as a fuel source. A study published in Metabolism compared fat and carbohydrate oxidation in two groups of runners — one that ate a high-carb diet, and another that ate a high-fat diet. Test results showed that fat oxidation during exercise occurred at more than twice the rate in the high-fat group, even at higher effort levels. For runners who like to go long, a fat-adapted approach may make sense. It's important to note, however, that runners switching to this type of diet anecdotally report a transitional period of reduced performance as the body learns to adapt.
You Are What You Eat
While these two marathon nutrition plans sound very different, they do both encourage runners to center their diets around healthy whole foods while avoiding processed junk. Another important factor is to watch calorie consumption carefully, regardless of whether they come from fat or from carbohydrates. This is because both BMI (according to PLOS One) and body composition (according to the National Institutes of Health) are directly tied to marathon running performance — higher BMI and body fat are linked with slower running times.
Interestingly, the best marathon nutrition plan of all may be a specific combination of the two. An Applied Physiology, Nutrition and Metabolism study found that when distance runners who trained on a high-carbohydrate diet switched to a high-fat, low-carbohydrate diet for up to two weeks prior to race day, their bodies became better adapted at using fat for a fuel source. However, it's important to note that the runners switched back to their usual high-carb diet for the 1-3 days immediately preceding the race.