Carb-Loading Before Racing & Training
Updated: Jun 15, 2022
As a dietitian and runner, I am all about optimising performance or training outcomes through fuel.
If you’re an experienced runner you will know how much more enjoyable a run is when you’re well fueled and properly hydrated. Getting your fuel right for your training runs might be the difference between your run being hard work and your run being really, really hard work which may of course influence how far and how fast you run in training. More importantly, if you’re running competitively, getting your race day fuel right can really improve your performance.
There are a lot of people sharing their opinion on the Internet, people who have written books and people trying to sell products that will try to convince you that their way is the right way but here I have summarised the best available scientific evidence on the optimum way to fuel yourself for performance and remember: nutrition is science, not opinion.
Fuel: The Basics
When we talk about fuel for exercise we are basically taking about carbohydrates.
The basic function of carbs in our body is to provide energy. I think we trap on about energy quite a bit but it is worth thinking about energy in our bodies in a more abstract way to help to understand it.
Just like all our electronic goods need energy in the form of electricity, our bodies need energy to function. Some electrical items like hairdryers, need a lot of electricity to function for short periods and some, like fridges need a small amount of constant energy. Our bodies are the same, our lungs, livers and other organs need a little bit of constant energy and when we exercise, our muscles, heart and lungs need a lot of energy.
The energy that our body uses is glucose which we get from carbohydrates in our food.
Carbs come in many different forms, from the complex starches like bread and potatoes, to the moderately complex like milk sugar, to the simplest forms like table sugar and syrup.
When we eat any form of carbohydrate our body gets to work to break it down to glucose.
As discussed, we need constant energy just for our lungs and our brains to function and for that reason, you use significantly more energy during a 6 hour nights sleep than you do during a 1 hour run. So in order for our bodies to continue to work at all times we have three ways of making sure glucose is always available.
The easiest way for our bodies to have glucose is when it is still in our bloodstream after a meal. In electrical terms, this is a relatively small supply that is sitting in the wires (I don’t know if that is possible electronically…but you get the idea).
When we eat more carbohydrate than we need at a meal (intentionally to fuel up or unintentionally because we’re greedy!) and we have more glucose than we immediately need, we store it in our muscles and livers as glycogen so that it is available later. Glycogen is a bit like a battery. Stored energy that will eventually run out. This is so important for endurance exercise because optimising glycogen stores allows us to keep up our pace when the glucose from the last meal has been used up - which is pretty quickly.
As a last resort, if all of the glucose in the blood stream is used up and the stored energy in the batteries in your liver and muscles is used up, we turn to our biggest source of energy - body fat. This is when athletes talk about ‘hitting the wall’ because fat has to be converted to glucose via quite a complex process so it delivers energy quite slowly and when you’re relying on it to fuel challenging exercise it doesn’t get to your muscles quickly enough which causes fatigue.
That said, if you’re trying to get your body fat percentage down, this is why fasted cardio is so challenging but so effective because you are forcing your body to use your fat stores rather than relying on glycogen. But that’s a story for another day.
So it’s the day before the big race and you want to optimise your performance. Clearly, it would be ideal if your diet had been perfectly balanced and meeting all your nutritional needs for the preceding months and years but for the purposes of this article we’ll focus on the last few days pre-race.
At this point, we want to concentrate on making sure that your batteries are fully charged (meaning your glycogen stores are replete) and that you have a plan to make sure that you’ve got some glucose in your blood stream at the start of the race.
So, for events that last 60-90 minutes, make sure you rest for 24 hours before, and the day before, consume 7-10 grams of carbohydrate per kilogram of body weight.
To give you an idea, a slice of bread is about 10g of carbohydrate, a large bowl of cereal is about 40g and 150g cooked pasta is 50g of carbohydrate so this is quite achievable.
If you’re running a full marathon or more, you will need to taper your exercise for a week leading up to the event and aim for 8-10g of carbohydrate per kilogram of body weight per day for 203 days before the event. Fortunately the days of heavy carb loading regimens are over!
On race day, in an ideal world, you would have a carbohydrate-rich meal of around 3g of carbohydrates per kilogram of body weight 3-4 hours before the event. Usually though, events are in the morning and getting up at 4am to eat pasta isn't usually that appealing, so if you prefer to sleep then just make sure you've had a carb-heavy meal the night before.
It is also important that you include your fuelling plans in your training at least twice because you don’t want to be surprised on race day by that that 4am bowl of pasta may have unwanted digestive effects at a suboptimal time!
For most people, avoiding a heavy meal 2-4 hours before racing is important but it is useful to have a high-carbohydrate snack 30-60 minutes before racing if you can tolerate it. We’re looking for 50g of quite refined carbohydrate at this point so a slice of toast or a couple of slices of malt loaf or yogurt and honey with a glass of orange juice would be ideal. This will provide you with that extra boost for the start of the race.
Another thing that has been shown to improve performance is caffeine. Between 3-6mg of caffeine (equivalent to about 2 cups of coffee depending on your weight) 40 minutes before races and training can be really effective. Increasing this dose doesn’t make any difference so please don’t start taking a fist full of caffeine tablets on the start line and make sure you trial using caffeine in your training before race day. If you’re not used to having caffeine or you know that you are particularly sensitive to it, don’t use it for this purpose.
During long distance races, performance can be improved by consuming 30-60g of rapidly absorbed carbohydrate per hour.
Good examples would be a bottle of sports drink or jelly babies which conveniently contain 5g carbs per sweet so it’s easy to make sure you’ve had the right amount!
The rest is down to sheer determination and good hydration!