Carbohydrates and fats are the primary fuel sources for running and ultramarathon running. Everybody has adequate fat stores to fuel any 50k, 50 mile, 100 mile or even 250 mile ultra and there is no need to eat extra fat to load up before an event. Carbohydrates are another story. Humans have limited stores of carbohydrates in our blood, muscles, and liver which can be depleted in any event longer than a 50k (and typically even in road marathons). We store carbohydrates in the form of glycogen (in muscles and the liver) and glucose (in the blood). A 70kg runner will have about 5g of glucose in the blood, 85g glycogen in the liver, and 300g of stored muscle glycogen. 

A well-trained 70kg runner will burn about 200-220g of glucose per hour in zone 2 (which most of an ultramarathon will be spent in). This means an average runner will deplete their stored glycogen/glucose in under 2 hours. It's important to remember the body never wants to run out of glucose completely and will force running pace to slow substantially well before glucose stores are exhausted. This means pace might have to slow 1 and a half hours into a race if not before. 

There are two main ways to extend this time to exhaustion and improve performance: carbohydrate loading before an event and consuming carbohydrates during the event. Today we are going to focus on carb loading. 

Carbohydrate loading has been around since the 1960s but has evolved over time as more research has been published. In the 1960 it was believed that you had to do a glycogen depletion phase first in order to have carbohydrate loading work, but that has since been proven incorrect. Modern carb loading consists of simply eating increased amounts of carbohydrates in the days leading up to an event/race.

Current research recommends eating 10-12g carbohydrates per kg body weight in the 36-48 hours before a race. 

For our 70kg runner, this would mean eating 700-840g of carbs per day (2800-3360 calories from carbohydrates!). Yes this is a lot and in order to eat that much carbs, we'd need to decrease the amount of fat and protein in your diet. It's recommended to decrease fat consumption and maintain moderate protein consumption. To eat this much carbs, you also want to think about eating less fiber filled foods. White rice, bread, pasta, cereal, pancakes, bagels, and sports drinks can be the easiest sources to eat. Fruit and fruit juices can also be consumed. 

Race morning, it is recommended to eat 1-4g carbohydrates per kg body weight, ideally 4 hours before race start. 

For our 70kg runner, this would mean eating 70-280g carbohydrates. Again limiting fat and fiber is recommended and moderate amounts of protein. 

A proper carb load will lead to significantly increased glycogen storage in muscles and the liver. Carbohydrate loading as described above can double glycogen stores in the body which can drastically improve race performance, especially in ultramarathon events. 

Below are lists of most common nutritional sources during ultra running training and racing to easily allow you to optimize your carbs per hour for peak performance. There is a list for each of these categories: Drink Mixes, Gels, Gummies, Bars and Waffles, and Whole Foods that list the amounts of carbs, sugar, protein, fat, and sodium in each product/food source. 

My goal is to make is easy for you to calculate how many carbs (and other nutrients) are you consuming with your current plan and be able to modify/improve your nutritional plan to optimize training and racing performance and recovery.

Related articles that are must reads to go along with this:
How to get high carbs per hour. 
How to Maximize Race Day Performance and Minimize GI Distress. 
​Carbs are King/Queen! 

We have all heard that carbs are king and we will feel better and perform better while consuming a high number of carbs per hour (60-125g/hour), but how do we do that? 

Step one is start looking at different foods and energy products to see how many carbs they contain per serving. Make a list of them so it's easy to calculate carbs per hour. 

Step two is look at the list and figure out which foods/products you know you already like and your GI system handles well. Figure out which foods/products you can eat per hour to reach your carb goal. 

If you're newer to high carb fueling, start with a goal of getting 60g carbs/hour. Some examples are below. ​

I am a big proponent of high carb intakes during training and racing and research backs this up also. Recently I ran the 28k at Big Alta by Freetrail and Daybreak Racing in beautiful Marin County, California and wanted to use my race as an example of high carb intake during racing. ​

First of all, the Big Alta is an amazing weekend of trail running and I would highly encourage you to go race or watch next year. 2024 was the first year of the race and it amazing. Race weekend was so fun with the 50k on Saturday and the 28k on Sunday. I watched some friends race the 50k on Saturday and hung out at some aid stations and the finish line and it was such a great vibe. Sunday I raced the 28k with a bunch of friends and had a blast. 

In endurance sport, including ultra marathon running, carbs are king/queen. Carbs are our primary fuel source and the one that allows us to perform at our best. Yes we are always burning some percentage of our calories from fat, but maintaining optimal levels of blood glucose through the regular consumption of carbs during endurance running is the only way to perform at our best.