Updated: November 21st, 2018

What you eat during the days before a race can have a big impact on your performance, especially for events that last 90 minutes or more.

If your training has gone well and you are well-rested, but you still find yourself slogging through the last few miles of a race, your pre-race diet is the likely problem.

Specifically, your glycogen stores are depleted and your muscles run out of energy.

In this article you will learn:

How to maximize your glycogen stores by carbo-loading
What foods to eat and what foods are best to avoid
How to adjust your training to increase your glycogen stores
Nutritional tips to maximize performance on race day

Suggested Reading: How to Eat to Fuel Your Running Training.

Fat and glycogen – fuel for running

Your body uses two types of fuel when you run – fat and glycogen. The fat comes from your body fat stores and even the leanest runner has several pounds of fat they can use for energy.

A single pound of fat contains approximately 3,500 calories – enough to power you through 35 miles of running. That means a runner weighing 160 pounds with 12% body fat is carrying about 19 pounds of fat which is enough calories to run 670 miles! In short – you won’t run out of fat during your race, even if it’s a marathon.

In contrast, glycogen is stored glucose. When you eat bread, pasta, rice, potatoes, oatmeal, or any other type of carbohydrate, your body breaks these carbs down into glucose and uses it for immediate energy. Any remaining glucose is stored in your liver and muscles as glycogen, and the excess is converted to and stored as fat in your adipose tissue.

Runners tend to be very good at turning carbs into glycogen and then storing it for later use but, even so, these stores are still relatively small – especially compared to your almost unending fat stores.

A long run can significantly deplete your glycogen stores, and if you run out of glycogen, your muscles are not able to work as well as usual.

As glycogen levels start to fall, your body will start to use protein and fat instead. This is not a good mix of fuels. You’ll start to slow down, your muscles will hurt, and you will encounter what runners call the wall. The wall can be hard to overcome and could even force you to drop out of your race.

Maximizing your glycogen stores will enhance your performance and help you to avoid (or at least push back) the wall. This is called carbo-loading.

Carbo-loading – two methods

There are two accepted ways to carbo load, a classical method and a more conservative method. Both options can work but, for most runners, the classical method is a bit too hit-or-miss.

Two methods of carbo-loading

The classical method

This protocol was first used in the 1960s and starts seven days before your race. You eat no carbs and then go out on a very long, hard run to fully deplete your glycogen stores. For the next three days, you rest and eat very little carbohydrate and then, for the final three days, you continue to rest but switch to a very high-carb diet.

The first three days prepare your muscles to synthesize and store more glycogen than normal, and the final three days supply your starved muscles with the carbs they need. Because of the preceding depletion, your body should store more glycogen than usual so that, on race day, your glycogen stores are full as possible. This is called supercompensation.

However, there are drawbacks to this method:

A hard run seven days before race day could mean you start your event feeling tired
No training for six days before your race could impair performance
Running with depleted glycogen stores is hard – both physically and psychologically. This is less than ideal preparation for a big race
Eating a lot more carbs than usual can lead to abdominal bloating and stomach upsets – the last thing you need on race day
Some runners find it all-but impossible to eat enough carbs in three days to restock their glycogen stores and end up with less muscle glycogen rather than more
This method is only effective if used occasionally – 3-4 times a year

The conservative method

With the conservative method, you reduce your training gradually over 7-10 days, while eating a little more carbohydrate than normal. During regular training your carbohydrate intake should 50-70% of your daily calorie intake. During your pre-race taper, you should increase this to 80-90%, or roughly 3-5 grams of carbs for every pound of your body weight.

Because you won’t be training as hard as normal, there will be more carbs left over for glycogen storage, and the reduction in training volume and intensity should mean you are well rested when race day finally arrives.

Unlike the classical method, you won’t have to do your last workout in an all-but fasted state, and nor will you have to suffer three days of low carb dieting. You won’t have to force-feed yourself carbs during the final three days either.

Because it is less extreme, you can use this method more often and should experience fewer if any negative side effects.

The best foods for carbo-loading

Your body can convert any carbohydrate into glycogen, but it’s a process that takes time. Too much glucose at once can lead to a “glucose glut” and fat gain. To avoid this, you should choose carbs that digest relatively slowly.

These are largely unrefined and have a low to moderate glycemic index. The glycemic index is a chart that categorizes carbs according to how quickly they are converted to glucose.

Good examples include: Brown rice, Couscous, Quinoa, Whole meal spaghetti, Oatmeal, Bran flakes, Muesli, Bananas, Apples, Dates, Oranges, Potatoes (sweet and white), Plantain, Pumpkin, Beans.

Tips for best results

Because glycogen is so critical, it’s very important that your stores are full on race day, and that means eating more carbs. Don’t leave it to the night before – the famed pre-race pasta party – that’ll be too late. Instead, start carb loading 7-10 days before your event to make sure you’ll have all the energy you need to perform at your best.

Here are a few tips to make sure you get the most from carbo-loading.

Practice your chosen carbo-loading method a month or so before your big race to make sure you don’t experience any adverse reactions. This is especially true if you want to use the classical method.
During the last few days before your race, eat lower fiber carbs as an excess of fiber can upset your stomach. White bread, white rice, and white pasta are better than their brown/wholemeal counterparts at this time.
Don’t worry about weight gain during carbo-loading. Glycogen is glucose bonded to water and any weight increase is just a little extra water retention which will disappear as you use your stored glycogen.
Don’t overeat carbs the night before or the morning of your race. Not only will this have very little impact on your glycogen stores, you also run the risk of having a stomach full of undigested food that could make you uncomfortable and hinder your performance.
Despite carbo-loading, you should still consume carbs and fluids during your race to minimize glycogen depletion and ward off dehydration.
Don’t try and load up on water as well as carbs. If you drink a lot more water than you need, your urine output will increase, and you could end up dehydrated. Adjust your fluid intake according to your thirst and just drink your normal amount – 2-3 liters per day.

Summary

If you run out of glycogen during your race, your performance will drop
Carbo-loading is designed to make sure your glycogen stores are as full as possible on race day
There are two accepted methods: the classical method and the conservative method
Both method work, but the classical method can be less reliable.
With both methods, you eat more carbs while reducing your training volume to increase glycogen
While your body can convert all forms of carbs into glycogen, low and moderate glycemic index carbs are best.
Weight gain and increased glycogen stores go hand in hand as glycogen is glucose bound to water. Any weight gained will disappear as your glycogen stores are depleted.