Why?
Carbohydrate is your bodies preferred fuel source, especially when it comes to high intensity or long duration (90 minutes +) activity. Fat also takes up a large component of the substrates used for energy during exercise. However, because it takes longer to convert into energy it’s less efficient and lends itself to lower intensity exercise.
So, it makes sense to fuel up on carbohydrates prior to a big race. This will ensure your muscle glycogen stores are full, therefore giving you a performance boost of ~2-3%. But how much? When? What type of carbohydrate?
How much?
There are varied opinions on the amount you should consume. This could depend on, experience, predicted time (ability level), muscle mass, body fat %, insulin sensitivity, previous intake, gender etc.
Typical recommendations are within the range of 8-10g/kg of body mass. Some suggest going as high as 12g/kg, but this should be restricted to very high-level endurance athletes. Some more conservative recommendation, range more from 5-8g/kg.
Lower (not eliminate) your protein and fat intake as it will slow down digestion and at this point in time we aren’t too concerned with body composition. This way calories aren’t increased too much, just a change in macronutrient ratios/proportion.
With consuming this much carbs, expect the number on the scales to go up! This is completely normal. Increased glycogen will cause you to store more water, therefore resulting in weight gain (1-2 kg/2-4 lbs).
When?
Many debate whether to do a depletion phase before carb loading. This is where you restrict intake before loading. However, the consensus in recent years is that this phase isn’t necessary.
2-3 days prior to the race is more than adequate. Some research suggests 1 day protocols are enough.
If you’re a serious runner, ideally you would have testing out some carb loading a few weeks prior to identify how you feel and what works best for you.
Eat little and often, big meals will have you feeling bogged down with food. The last thing you want on the start line is the feel lethargic.
Don’t eat a big meal late at night, it might not digest very well and may disrupt sleep. Try to get most if not all your carbs in before 6pm.
Morning of the race, eat well in advance e.g. 2 to 3 hours before the start to avoid any discomfort. Still carb heavy, to maximise readily available, not just stored carbs.
During the race, especially past the point of 90 minutes, top up your energy by using energy gels and sports drinks etc. Carbohydrate mouth rinses have also been found a useful tool.
What type?
Pasta, Oats, Bread, Rice, Bagels, Potato, Cereal……
However, consider fibre content and volume of food. Too much fibre can cause gastric distress (stomach issues). With regard to volume, per 100g of potato there is roughly 17g of carbs. For a 70kg male to eat 700g of carbs from potato, they would need to eat over 4kg of potatoes.
Incorporate some carbs with less fibre and volume – think easily digestible, think higher sugar (but don’t go mad on junk). In essence, strike a balance between whole food sources and sugary extras.
Try not to eat drastically different foods, stick to preferred choices you know your body will tolerate.
Typically I would advise against large quantities of fruit for carb loading as it’s broken down into a sugar called fructose which is metabolised into liver glycogen, not muscle glycogen.
References:
Burke, L. M., Hawley, J. A., Wong, S. H., & Jeukendrup, A. E. (2011). Carbohydrates for Training & Competition. Journal of Sports Sciences, 29(sup1), S17-S27.
Hawley, J. A., Schabort, E. J., Noakes, T. D., & Dennis, S. C. (1997). Carbohydrate-Loading & Exercise Performance. Sports Medicine, 24(2), 73-81.
Hawley, J. A., & Leckey, J. J. (2015). Carbohydrate Dependence During Prolonged, Intense Endurance Exercise. Sports Medicine, 45(1), 5-12.
Spriet, L. L. (2014). New Insights into the Interaction of Carbohydrate & Fat Metabolism During Exercise. Sports Medicine, 44(1), 87-96.
Stellingwerff, T., & Cox, G. R. (2014). Systematic Review: Carbohydrate Supplementation on Exercise Performance or Capacity of Varying Durations. Applied Physiology, Nutrition, & Metabolism, 39(9), 998-1011.
Bussau, V. A., Fairchild, T. J., Rao, A., Steele, P., & Fournier, P. A. (2002). Carbohydrate Loading in Human Muscle: An Improved 1 Day Protocol. European Journal of Applied Physiology, 87(3), 290-295.
