What is Carbohydrate Loading?
Carbohydrate loading or carb-loading is a nutrition technique used by athletes in an attempt to prolong optimal athletic performance and delay the onset of fatigue, or, ‘hitting a wall’.
Transforming Carbs in Food to Energy for Muscles
Throughout digestion, carbohydrate-containing foods are broken down into simple sugars such as glucose. These sugars are then absorbed into the bloodstream. A hormone called insulin is secreted by the pancreas which enables uptake of glucose from the blood by our liver and muscle cells, where it is stored as potential energy in the form of glycogen.
Your muscles are basically fuel tanks for glycogen. Carb-loading if done right, essentially allows you to store the maximum possible amount of glycogen or “fuel” for later use.
Successful carb-loading puts the muscle into a state of ‘supercompensation’, allowing you to hold up to twice the normal resting level of stored muscle glycogen.
From this stored form, the body can transform glycogen back into glucose through a process known as glycolysis, and provide energy when needed.
When is Carbohydrate Loading Appropriate?
Carbohydrate loading is beneficial for athletes competing in endurance events such as triathlon, iron man, cycling, and distance running where sustained efforts for long periods burn through muscle glycogen.
However, it is not only endurance sports that can experience benefit from a high carbohydrate intake in the lead up to an event. This is particularly true if there has been a recent training session or if there are multiple events within a short time frame (ie playing multiple games in a 3-day period).
Energy production during brief sprints (like those done in team sports such as soccer or rugby), is derived from the breakdown of phosphocreatine and muscle glycogen (anaerobic metabolism). Extended periods of multiple sprints eventually drain muscle glycogen stores, resulting in decreases in power output and reductions in general work rate during both training and competition.
Carb-loading is also utilised by bodybuilders in order to appear their ‘most muscular’ on stage. The extra glycogen and water that is stored in the muscle from carb-loading increases the visual appeal and physical size of their muscles for competition.
How to Do It
It used to be believed that you had to first deplete your muscles of glycogen to take advantage of their compensatory carbohydrate loading effects. Recent research has shown that this step is not necessary.
Current best practice to carbohydrate load can be simplified to:
Increase carbohydrate intake to 10–12 grams of carbohydrate per kg of body mass per day, for 36–48 hr leading up to the event. This will saturate your muscles with a maximal amount of glycogen.
Reduce training in days leading up to the event to ensure muscle glycogen is not being depleted, and complete rest is often advised the day before the competition.
- The amount and type of carbohydrate that people can tolerate without stomach upset
- There will be an additional weight increase due to the physical weight of the increased stored glycogen as well as the water weight that goes along with this (approximately 3g of water is stored per 1g of glycogen)
- During an overnight fast (ie the time you are sleeping) liver glycogen stores are reduced substantially, potentially up to 80%. A pre-event carb-rich meal and/or snack will help restore liver glycogen and ensure fuel availability
Sources of Carbs
Consuming so much carbohydrate for multiple days, or even one day can be difficult, so it is worth considering where these carbs are coming from.
Carb-loading is often done in conjunction with a low residue (i.e. a low fibre) diet. Utilising a lower fibre intake can help in multiple ways:
- Reduce the risk of gut issues during the race
- Achieve a small reduction in body weight due to less ‘residue’ in the gastrointestinal tract/bowels (this can also partially offset the mass of the additional muscle glycogen and stored water from loading)
- Help prevent feelings of fullness which may otherwise prevent you from being able to eat more during the loading phase
Suitable foods include easily digestible carbohydrates that are lower in fibre, palatable to the person eating them, and that are unlikely to cause stomach upset. Foods that wouldn’t often be recommended in a healthy diet such as sugary liquids and simple sugars/high GI foods can often be useful when carb loading.
Do’s and Dont’s
It is important to note that foods, especially when eating large volumes such as with carb-loading, can have differing effects on the body. It is therefore important that you trial foods before the event -like a ‘training run’ – to ensure there are no unforeseen gastrointestinal disturbances.
High fibre foods like grain bread, wholemeal pasta, brown rice, and large amounts of fruit, can cause gastrointestinal upset including constipation or diarrhoea, flatulence, and bloating which are all very uncomfortable sensations, particularly during vigorous exercise. These should be avoided where possible.
An important factor to be aware of is that trying to carb-load without a plan can make it difficult to consume enough carbohydrates to optimise performance.
For example, a 70kg athlete consuming 3g/kg/day might increase to double their carb intake to “carb load” and eat 420g of carbohydrates. Without a plan, this is still well under the 10-12g that is recommended, and this might not be enough to maximise performance.
This can occur if you are consuming higher fat or higher fibre carbohydrate sources, and getting full too quickly, or simply lacking awareness of how much carbohydrate is actually required. Keep fat intake low, and protein moderate.
Do some simple planning to ensure that sufficient carbohydrate intake is met. It is important to remember that carb-loading is not meant to represent a healthy diet. It is a functional method of temporarily enhancing performance and foods that may be recommended on a carb-loading plan are definitely outside of normal dietary recommendations. With that being said, a daily breakdown may look like this:
When NOT to Carb-Load
Remember, carbohydrate loading is typically only useful for events that place a very high demand on the body and its energy systems for a sustained time, or for repeated high-intensity bouts over consecutive days when glycogen depletion becomes a limiting factor.
It is not necessary for your Sunday 4km jog, your weekly touch footy game, nor every causal gym session you do. These sorts of events will benefit from having carbohydrate in your diet in general, but they don’t need to be ‘loaded’ for.
One-off short-duration events, or single short game/competition situations are unlikely to benefit from carb-loading. Unnecessary carb-loading can definitely promote excess weight gain if not being utilised correctly.
Tyler has a Bachelor of Nutrition and Exercise Sciences and completed his Masters of Dietetics through the University of Queensland after moving away from a long career in the fitness industry. As part of his education he worked with dietitians at the Brisbane Broncos rugby league club, is currently working with the Qld Women’s Rugby 7’s team, and has continued to follow his passion for performance nutrition.
Tyler is a believer in ‘practice what you preach’. Outside of helping people achieve their goals through diet and exercise, he competes in powerlifting and loves experimenting with his own nutrition and diet to find the best ways to support various training and body composition goals.