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Marathon Training: Are You Eating Enough Carbs?

I’m going to state the obvious here, but running a marathon and half marathon are very different then running a 5K or 10K. I’m not talking about the difference in distance — I’m talking about the difference in nutrition needs. For the most part, nutrition isn’t a limiting factor to performance for the 5K and 10K, but once you get over two-hour mark in racing, nutrition play a vital role in how well you perform.

As a runner, if you want to perform at your best, you need to start thinking about the food you eat as sources of nutrients: carbohydrates, proteins, fats, vitamins. Each of these nutrients plays a crucial role that either supports or inhibits energy production, recovery and health.

I’ll be focusing mainly on carbohydrates because they are by far the most important nutrient for marathoners. Carbs are your body’s main source of energy: They aid in fat metabolism (a.k.a. using fat as a fuel source), and they prevent protein from being used as energy. A diet low in carbohydrates will certainly prohibit performance.

Carbs figure in to the two essential parts of marathon nutrition: daily nutrition and long-run nutrition. Let's break them down below.

Daily Nutrition

Daily nutrition is what you need to eat everyday in order to maintain healthy nourishment and support daily energy and recovery requirements. Everything you eat throughout the day falls into this category: breakfast, lunch, dinner and snacks. For the most part, these needs are all the same — a healthy balance of all nutrients —but it’s the amount of each nutrient needed that changes for people training for a marathon.

Since carbohydrates are the main source of fuel for endurance events, you’ll need to be sure to have a diet high in high-quality carbohydrates. If your total carbohydrate intake is insufficient, you’ll start to feel excess fatigue, like you’re constantly running on empty. To avoid the crash, your daily carbohydrate intake should be directly tied to the amount of training you do. Current recommendations are:

  • 3 to 4 grams of carbs per kilogram of bodyweight for 30 to 45 minutes of exercise

  • 4 to 5 grams of carbs per kilogram of bodyweight for 46 to 60 minutes of exercise

  • 5 to 6 grams of carbs per kilogram of bodyweight for 61 to 75 minutes of exercise

  • 6 to 7 grams of carbs per kilogram of bodyweight for 76 to 90 minutes of exercise

  • 7 to 8 grams of carbs per kilogram of bodyweight for 91 to 120 minutes of exercise

  • 8 to 10 grams of carbs per kilogram of bodyweight for more than 120 minutes of exercise​​

To be clear, we're talking about complex carbs here — not plain ol' white sugar, which is a simple carbohydrate. Complex carbs are ones that are accompanied by other nutrients, particularly fiber, so they are more filling and satisfying. Examples are steel cut oatmeal (Note: not the instant kind), whole grains such as farro, quinoa, bulgur, brown rice (not white); and beans or lentils such as black beans, pinto beans or kidney beans.

One other thing to note is that protein is also an important daily nutrient. That's because protein contains amino acids, which are a necessary building block for muscle growth and recovery. Exact amounts vary person to person, but it is suggested that runners consume somewhere between 0.7 to 1.0 grams of protein per pound of body weight. Aim to get your protein allotment in smaller doses throughout the day.

Long-Run Nutrition

Long-run nutrition is what you take in while you’re running. Just like a gas tank in a car, your body has an upper limit as to how much fuel it can store in the form of carbs and fat. Because of this limit, most runners will need to take in carbohydrates while running. While exact amounts will vary it is recommended most runners consume 30 to 60 grams of carbs per hour of exercise. (Note: Gu Energy Gels average about 22 grams of carbs per packet.) It’s important you start taking fuel in with the first hour to avoid hitting the wall later.

The key here is practice this during your long runs so when it comes to race day you’ve ironed out exactly when you’ll take in fuel, and what kind of fuel works best for you.

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