Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In



Carb Up To Crush Your Runs

There's a lot of confusing carb information out there. Thankfully, our RDN is here to clear things up.

Lock Icon

Become a member to unlock this story and receive other great perks.

Already have an Outside Account? Sign in

Outside+ Logo

All Access
Fall Sale
$1.52 / week*

  • A $500 value with everything in the Print + Digital Plan plus 25+ benefits including:
  • Member-only content on all 17 publications in the Outside network like Outside, SKI, Backpacker, Clean Eating, and more
  • Today’s Plan training platform with customized programs
  • Gaia GPS Premium with hundreds of maps and global trail recommendations, a $39.99 value
  • Professional race photos from FinisherPix
  • Annual subscription to Outside magazine
Join Outside+
Trail Runner Magazine

Print + Digital
Special Price
$0.50 / week *

  • Annual subscription to Trail Runner magazine
  • Access to all member-exclusive content on
  • Ad-free access to
Join Trail Runner

*Outside memberships are billed annually. You may cancel your membership at anytime, but no refunds will be issued for payments already made. Upon cancellation, you will have access to your membership through the end of your paid year. More Details

When it comes to food and nutrition, we tend to overcomplicate things.  Eat this, not that. Run fasted, restrict sugar.   Unfortunately, much of the controversy stems from observations and sensationalized media headlines vs. actual data, leaving the consumer more confused from their Google search than they were before. 

One of the top casualties of this confusion is carbohydrates. Instead of enjoying our bread, pasta, or cookies, athletes might restrict food for performance and weight loss and feel a twinge of guilt every time they attend to their hunger.

RELATED: Trail Runner’s Guide to Carbohydrates

What are Carbohydrates?

Carbohydrates can be divided into three types: sugars, starches, and fibers that are found in food.  When you eat carbohydrates, they are broken down into glucose, fructose, and galactose. Once broken down, they are taken into cells and used to create adenosine triphosphate (ATP) through two processes called glycolysis and cellular respiration. ATP is what allows you to perform and run efficiently.   

RELATED: Understanding Glycogen, Your Body’s High-Performance Fuel

What about Carbohydrates and Running Performance?

Our bodies are smart.  They store carbohydrates in our muscles and liver to use for energy production when we are sleeping, in between meals or exercising. The average runner stores about 2,000-2,500 calories worth of carbohydrates, while a trained athlete might be able to store a bit more.  On average, that would keep you running for about 90 minutes to 2 hours!

Once you run out of stored carbohydrates, without an additional intake of carbohydrates (like taking a gel), the body will shift to using solely fat stores (fat oxidation) and protein (muscle) for energy production.  Unfortunately, the process is much slower, resulting in feelings of mental fatigue and reduced output – meaning, you’re going to go slower.  Injury risk also increases as muscle protein breakdown increases.  

When you run, you are always using some carbohydrates and some fats for fuel.  The contribution percentage of each of these macronutrients depends on the exercise intensity you are performing.  The higher intensity you are going (ie higher percentage of your VO2max), the more carbohydrates your body prefers for energy production. 

In the running world, there is a popular idea that training on low glycogen stores will improve long-term fat oxidation rates, allowing the body to spare glycogen stores and reduce the need for as much outside carbohydrate intake.  

RELATED: Should Women Fuel Differently Than Men?

Risks of Carbohydrate Restriction?

Knowing what we know about carbohydrate manipulation and training, if a runner still is considering carbohydrate restriction as a means to improve training, we still need to consider the downsides of carbohydrate restriction.  

In a sport that already has a high incidence of Low Energy Availability (LEA), restriction of any macronutrient (carbohydrates included) can perpetuate the idea of undereating and be detrimental to long-term health and performance.  Long-term LEA can lead to altered hormones (low testosterone in males and functional hypothalamic amenorrhea (loss of period) in females).  These conditions alone are associated with impaired risk of bone injuries, cardiovascular disease, and decreased ability to train and recover.  

RELATED: Ask The Coach: Long Run Fatigue

So what should you do?

At this time, there’s not enough evidence to recommend carbohydrate restriction for performance.  That doesn’t mean it won’t work for some runners, but, you should take into account the negative health impacts, including to mental health, when making dietary decisions.

Overall consensus: Eat the cookie!