How to effectively carbohydrate load for optimal race performance

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.