3 things runners need to know about carbohydrates

Learn to balance carbs with protein and healthy fats

women running

One of the biggest nutrition topics runners ask about is carbohydrates.

  • Why do we need them?
  • When should I eat them?
  • When should I not eat them?
  • Which carbohydrates will make me fat?
  • Which carbohydrates are good?
  • Should I try a low-carb diet?

This article is going to delve into why runners need carbohydrates, why runners need carbs on the run and which ones are best, and why it might be beneficial to train without food some of the time.

Despite the fact that all athletes’ nutritional needs are different, most runners need to follow a diet that is high carbohydrate for the best training and racing results. I work with athletes all the time to help them determine how to fuel their bodies with enough carbohydrates, protein and fat from real food without overdoing it.

While most athletes can (and should) focus on carbohydrates for the majority of their calories, it is important to stress the fact that as an athlete, you are an experiment of one — you get to decide what diet, training schedule and recovery methods work for you. For example, there is plenty of anecdotal evidence that a high fat/low carb diet may work for some endurance or ultra-endurance athletes, but here I am making the recommendations for a higher carbohydrate diet for runners, based on the fact that your muscles’ preferred fuel source is carbohydrates/glucose.

1. Daily carbohydrate needs

There is a huge emphasis for runners to get lots of carbs in their diets to help them run. Honestly, carbohydrate intake is sometimes overemphasized. Carbs before running, during running, after running, all day after a run — runners often neglect protein and healthy fats. That is not to say carbs aren’t important. Carbohydrates from food are stored in the body as muscle and liver glycogen, which is used as fuel during exercise.

At low intensities, a greater amount of fat is used as energy (though carbohydrates are always being used), but as exercise intensity increases from low to moderate/high intensity, the use of fat as fuel decreases and carbohydrates are used as the primary fuel source. Well-trained muscles can store even more glycogen, which is good news for endurance athletes who need that energy at mile 20 and beyond.

Fueling an endurance athlete through training and racing requires about 2.5-4.5 grams per pound of body weight, or 55-65% total diet from carbohydrate (compared to 2.5-3.0 grams/pound for moderate exercisers and more than 4.5 grams/pound for ultra endurance athletes).

Many athletes like to “bookend” their training with those carbohydrates, which is the time our bodies need the carbs the most:

  • Eat breakfast sometimes (granola bar, cereal with milk, oatmeal, a banana with peanut butter, toast)
  • Fuel with carbohydrates during long runs sometimes (Gu, gels, chomps, candy, etc.)
  • Refuel with a mix of carbs and protein post-workout

Don’t neglect those carbohydrates right after a workout — whether it’s a post-workout snack or a full meal that contains carbohydrates and protein. This meal is important for recovery so athletes can accomplish their goals at their next workout.

2. The science of mid-run carbs

Once a workout goes over 90 minutes, glycogen/stored carbohydrates can get drained, especially for a moderate to hard intensity, prolonged workout. Eating some sort of carbohydrates on a run will help athletes to spare their glycogen stores, keep blood glucose from dropping and can help replenish glycogen stores before the next training session, therefore helping you perform better on training runs and at races.

During a training run or competition, aim for 40-60 grams of carbohydrate per hour (120-240 calories/hour) after that first hour of running. Most carbohydrate energy products (Gu’s, gels, chomps, etc.) contain different types of sugars, so it is important to practice with many different types of carbohydrate fuels during training to experiment with how your body will respond to the different fuels.

Some people may bring regular candy on their training runs, like gummy bears, but those pre-made carbohydrate products are usually formulated with electrolytes and also mix different types of sugars, allowing the body to absorb more carbohydrates per hour (more than 60 grams per hour).

Many carbohydrate products on the market contain maltodextrin (a very quickly and easily-digested carbohydrate) and a different type of sugar (simple sugars like glucose and fructose). Anything above what the body can absorb and use may cause gastrointestinal distress, so it’s important to practice fueling during training runs. I recommend practicing with many different types of carbohydrate fuels (solid, liquid, gels, different brands) to see how your body responds to them.

Check the label for this GU energy gel, containing maltodextrin and fructose for sugars + electrolytes at about 100 calories , 23 grams of carbohydrates.

Salted Watermelon Gu:
INGREDIENTS: Maltodextrin, Water, Fructose, Leucine, Sea Salt, Citric Acid, Natural Flavor, Potassium Citrate, Sodium Citrate, Calcium Carbonate, Valine, Green Tea (Leaf) Extract (Contains Caffeine), Gellan Gum, Isoleucine, Sunflower Oil, Sodium Benzoate (Preservative), Potassium Sorbate (Preservative).

3. Try training low, some of the time

As mentioned above, carbohydrates stored in the muscles and liver, in addition to any carbohydrates eaten on the run help runners keep their energy levels high, prevent blood sugar from dropping and help replenish glycogen levels for speedier recovery. This is especially true as intensity increases — when runners are pushing the pace or climbing a hill (anything at a higher intensity), they’re burning carbohydrates. Having full glycogen stores and eating carbohydrates on runs over 90 minutes helps to delay fatigue and “hitting the wall” by sparing the glycogen stores from getting depleted. Once glycogen stores are depleted, fat becomes the primary source of fuel for exercise.

Endurance training increases the body’s ability to oxidize fat, which in theory can help runners prolong endurance exercise without depleting their glycogen stores. It is more difficult for our bodies to use fat for energy, and if given the choice, muscles prefer carbohydrates to use for energy, but many athletes want to be able to burn more fat, to run longer in training and races without taking fuel with them or without “hitting the wall.” Being able to burn more fat means being able to tap into the nearly limitless fat reserves (50,000 to 60,000 calories of triglycerides stored in your body, compared to only about 2,000 calories of total body glycogen stored). In fact, some recent studies have looked into “training low,” or restricting carbohydrates for workouts. The research right now isn’t strong enough to say that eating a high fat diet benefits performance, and in fact, repeatedly performing with low glycogen stores have been shown to decrease endurance, especially at high intensities.

So, train low or no? It’s not so black and white.

Regardless of research, athletes can use the “train low” strategies to train their bodies to use fat more efficiently on runs.

They can to include some fasted workouts into their training schedule (not more than 50% of runs) to promote training adaptations and work their fat metabolism versus training each and every time with carbohydrates. According to Nancy Clark’s Sports Nutrition Guidebook, runners can try training with lower glycogen levels when they have a lower-intensity workout and keep themselves fueled for any high-intensity workouts.

Athletes can try eating a normal (higher carb) dinner the night before a long, slow training run, and wake up and run before breakfast, just taking water with them on a their runs. Most runners have enough energy to run at least 90 minutes, but may have to build up to running without fuel if they are used to usually running after eating. Athletes can also try training more than once a day, with that second training session being a low glycogen workout. Make sure to refuel right away after a workout to promote muscle recovery and glycogen storage.

Remember: Everyone is different

These strategies may not work for everyone, and likely will not work for every run. If someone is a very speedy marathon runner, a low-carb run or diet may not fit into their training. For best results, working with a registered dietitian with experience working with athletes can help you decide the best strategies to help you fuel your workouts.

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