Carbohydrate loading

What is carbohydrate loading and why do people do it?

Carbohydrate loading is a nutrition strategy used by endurance athletes to maximise their muscle glycogen stores (i.e. ensuring their fuel tank is topped up as much as possible). This typically starts a couple of days prior to their endurance event in conjunction with tapering off in training.

Carbohydrate loading can extend the duration of steady-state exercise by ~20%, and improve performance over a set distance or workload by 2-3% (Hawley et al 1997b).

With maximal fuel on board, it makes sense for one to be able to last longer before fatigue sets in. This applies for exercise events lasting more than 90minutes - when muscle glycogen starts to get depleted and energy production becomes limited by the amount of carbohydrate you eat during your race.

Who would benefit from carb loading?

If you are participating in endurance events lasting more than 90 minutes, you would likely see a performance improvement on race day if you carb load. That is, if you have been consuming adequate energy and carbohydrate in your day-to-day living as well. If energy availability is low and carbohydrate intake is low during training, you may not be responsive to carbohydrate loading leading up to their event.

When to start carb loading?

Muscle glycogen typically gets replenished within 24-36 hours in the absence of muscle damage. That's why the carbohydrate loading phase goes hand-in-hand with tapering to ensure minimal muscle damage for maximal glycogen storage and starts ~2 days before race day.

However, in reality, carbohydrate loading involves careful planning, trialling in training, training the gut to optimise tolerance (i.e. minimise gut issues), making tweaks and then finally executing it 2 days prior to race day. So, when you sign up for that endurance event and commit to a training plan, that is the time to engage the support of an Accredited Sports Dietitian and work out your nutrition plan for training as well as race day.

How to carb load?

It really depends on you and what amounts of carbohydrate you can tolerate without feeling too full or experience gut issues. The general guide is to aim for 10g CHO/kg/day (CHO = carbohydrate) but that depends on what your usual carbohydrate intake is like and if you need extra time to adapt and work up to a higher carbohydrate intake.

If you haven't had the chance to try carb loading throughout your training and don't know what e.g. 10g CHO/kg/day looks like for you in terms of food, you may be in for a shock. But don't panic, you can still 'carb load'. Just have more carbohydrate foods across the 2 days at every meal and snack, more than you usually would. Be guided by your comfort level. Aim for lower protein, fibre and fat. Just remember, without a carb loading plan, you may not be eating enough and may 'hit the wall'/'bonk' during your race. So then, you really need to focus on race day nutrition to make sure you have enough fuel throughout your race (at least get this planned out -> aim for 30g-60g CHO/hr during the race).

An Accredited Sports Dietitian can support you with your nutrition and take the stress out of trying to figure it out yourself. Give yourself 3-6 months when working with a sports dietitian to fine tune your nutrition plan as you would likely be doing tweaks along the way to find that sweet spot that works for you. The nutrition knowledge and skills you gain alongside a sports dietitian can assist you in becoming independent in planning future races. Having a nutrition and hydration plan sets you up well and ready for race day.

References:

Hawley JA, Schabort EJ, Noakes TD, Dennis SC. Carbohydrate-loading and exercise performance: an update. Sports Med 1997b;24:73-81.