Marathon Nutrition 2. Race fuelling - start NOW.



This probably wasn’t the second blog you expected but with only 10 weeks to go, you need to get on with this now. Race nutrition is an aspect of marathon nutrition many leave until too late. I get quite an influx of emails with only a few weeks to race day to go wanting to discuss a fuelling strategy. Big no no! This is far too late. You need to start now.

Why Carbohydrate?

It is well documented that the main cause of fatigue in exercise over 60 min is diminishing energy stores. Our body mainly uses carbohydrate and fat for energy. Although we use a mix of both energy sources, carbohydrate is the preferred source as it is more readily converted to energy than fat. We generally have a small amount of glucose circulating in the blood, with most being stored in the muscle and liver as glycogen. However, herein lays the problem. We only have enough stored carbohydrate to last about 90 min of exercise, compared to fat where energy stores should theoretically power a runner for at least 1300kms! Some may be thinking, “Rely less on carbs and become more proficient at using fat for energy”, a growing trend in the Ultra community and a debate and blog post in itself. However, the importance of carbohydrate in exercise performance has been reported as early as 1939 (1), and one should not ignore the endless number of studies since that prove carbohydrate taken during prolonged exercise increases time to exhaustion. In simple terms, when glycogen stores become depleted, your muscles and brain run out of fuel, making us feel exhausted and drained. In an ideal scenario, if we take carbs when on the move we minimise this depletion by keeping the blood sugar level up, keeping stores a plenty and energy levels flowing.

When to fuel?

The longer we can preserve our stored carbohydrate, the better we will be fuelling when we race. If we can keep our blood sugar levels topped up, we can keep saving our stored carbohydrate for later in the race. With this in mind, it is important to maintain your energy levels as early as possible in the race. If you are waiting to take your first gel or drink until an hour into your run, your glycogen stores will already be getting low. The key is to start early at about 20 minutes into the race. Although you won’t necessarily be feeling low on energy, topping up the tank from the word go will only benefit you later in the race where fuelling may become harder due to fatigue and potential stomach problems.

How much to fuel ?

The American College of Sports and Medicine give a general recommendation to take between 30-60g of carbohydrate per hour during prolonged exercise (2). These recommendations are based on the fact that the body cannot absorb more than 60g of carbohydrate per hour (1g/min) when ingesting a single carbohydrate source such as glucose. However, during further prolonged exercise (those of you that run longer than 2.5hrs), if a “multiple” or “dual” carb source is consumed such as maltodextrin:fructose together, we can utilise up to 90g/hr instead of 60g/hr with a single source carb. This is because the two different types of carbs (maltodextrin + fructose) use different intestinal transporters for absorption hence increasing carbohydrate delivery and use. In reality though, this is a large amount of carbohydrate and probably not managed by many, but you can train your gut, so practice in training will see what you can tolerate. In light of all of this evidence, does it mean that if you can’t manage these amounts all is lost? The answer is no. A study by Maughan et al (3) found an intake as low as 16g/hr improved performance by 14% compared to water intake alone. If you find you really struggle to tolerate anything apart from water, evidence has suggested that even rinsing the mouth with a carbohydrate drink (without swallowing) could trick you brain into thinking it’s receiving energy and have an improvement on your performance (4). It can’t do any harm to try!

What to fuel with?

This is where individuality rules! First up is to experiment and see what works for you. Gels, energy chews, sport drinks, bars, real food…it is personal choice and down to tolerance and taste. Sports products are designed for fast absorption and ease of use but some people dislike them and find real food is the way forward. Sports drinks tick both boxes of fuelling and hydration and are a good base for your fuelling plan. If you are doing a race that provides drinks and food, find out what they are and train with that specific brand. This may mean that you can rely on the pit stops rather than carrying your own. Avoid anything that has high levels of protein or fibre, such as some energy bars, as these will slow down the absorption rate of your needed carbohydrate.

Practical Top tips

1 The science provides the guidelines but be flexible, as no matter what the science says, you are more constrained on the day by what your stomach dictates.

2 Find out what products are available on the course, training with them may mean you can rely more on check point nutrition.

3 Use your long training runs to conduct experiments of how much and what type of fuel you can tolerate.

4 To start, trial 20-30g carbohydrate per hour, little and often and aim to work up to 50- 60g/hr….remember your gut is trainable.

5 Set your watch time to bleep every 20-30 mins to remind you to fuel.

6 Start fuelling early whilst the gut is fresh and absorbs carbs easily, things might not be so easy a few hours into the race!

7 The Golden Rule - don’t do anything new on race day no matter how tempting they may look.


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