With the autumn marathon season upon us, it is time to think about race week nutrition. If you have been training for a marathon or any endurance event you have probably heard people talking about carbohydrates and carbohydrate loading or carb loading for short. But what is carb loading? How do you do it? Does it matter for race day? These are just a few of the questions we will be covering today. By the end, you will feel confident in knowing what carb-loading is and how you complete the load during the lead-up week.

What is carb-loading and why does it matter?

Carb-loading is the process of increasing the amount of carbohydrates you eat in the days leading up to a marathon. It ensures the muscles in your body are holding onto as much glycogen as possible. When we eat carbohydrates they are broken down within the body into glucose and then stored in our muscles as glycogen. Glucose is the body’s preferred energy source especially when doing events like marathons. 

Ensuring your body has adequate amounts of glycogen stored helps to ensure you don’t hit the wall during the marathon. A carb-load when done well can also have a significant benefit on your performance and has been proven to increase performance by 2-3%¹. To put this into perspective if you are aiming for a 4-hour marathon this could lead to you running 4-7 minutes faster.

When to start carb-loading?

You’ve probably seen advertised pasta parties the night before a marathon and might be thinking ‘ok so that’s all I do eat loads of pasta the night before’. But it’s not that simple. You want to increase your carbohydrate intake for 3-4 days before the marathon. This will ensure that your body has adequate glycogen stores and that you are replacing any you are using during your taper runs.

How many carbohydrates do I need?

The recommended amount of carbohydrates to consume per day is 10-12g per kg of body weight (3.6-4.5g per pound of body weight). For a 60kg individual, this would mean consuming between 600-720g carbohydrates per day. I know this seems like an overwhelming amount of carbohydrates to consume.

Weight (Kg)	Total number of carbs
50	500-600
55	550-660
60	600-720
65	650-780
70	700-840
75	750-900

Don’t increase your food intake

When doing a carb-load you don’t want to increase the overall amount you are eating. You just want to increase the carbohydrate content of your diet and in turn fat and protein will reduce. High levels of fat in your diet in the lead-up to the marathon can cause GI distress especially if it is not something you are used to.

Do increase your fluid intake

You will find that you need to drink a little more during this period. For every gram of glycogen stored our body stores 3-4 grams of water. This isn’t a bad thing as it will help our body be hydrated for race day. It can cause a slight weight gain on the scales but this is not something to be concerned about. If you are sensitive to the number on the scales then best not to weigh yourself during this period. The weight gain is not fat being stored within your body it is the water weight associated with the increased glycogen stores which will disappear as you use the stores.

Limit fibre during this period

Another thing you want to avoid during your carb-loading period is a high-fibre diet. Reducing the amount of vegetables consumed will help decrease the amount of fibre in your diet. This will also help prevent GI distress on race day itself.

What foods to enjoy during a carb-load

Some good foods to include during the carb-load period include:

• White rice
• White pasta
• White bread
• Fruit juice
• Fruit smoothies
• Pretzels
• Sweets
• Sports drinks

What foods to avoid

You want to limit foods that are high in fat or fibre including:

• Whole grain bread
• Whole grain pasta
• Muffins
• Crisps
• Pizza
• Creamy sauces
• Pastries

What does a carb-load day look like?

Here is a sample day of eating for someone aiming to consume 500g of carbohydrates:

On the above mentioned sample you would consume 515g carbohydrates.

Recap

• Doing a carb-load prior to your marathon can increase performance by 2-3%
• Start increasing your carb intake 3-4 days out from the race
• Eat easy-to-digest simple carbs such as white pasta
• Go easy on foods high in fibre such as too many veggies and whole grains
• You are aiming for 10-12g carbs per kg of body weight

Other articles mentioned in this blog post:

1 – Carbohydrate Loading and Exercise Performance: An Update