What is carb loading, and how can it benefit you?

Fueling is one of the most important aspects in maximizing athletic performance. Without adequate fuel, we can’t generate the energy needed to reach peak or sustained performance, which is especially true in endurance and ultra endurance sports.

In fact, when it comes to carbohydrates, it’s well established that performance over prolonged exercise, such a middle — long-distance running, cycling, or cross-country skiing, is heavily influenced by the availability of muscle and liver glycogen.

With this in mind, I was very surprised to read a recent study by Mendes et al 2025 showing a whopping 50% of elite triathletes do not take advantage of pre event carbohydrate loading strategies! Reading this, it struck me that it’s probably not just triathletes who may not be aware of the benefits of “filling the tank” before a competition. So let’s discuss the various strategies for glycogen super compensation (commonly referred to as carb loading) and how it can benefit you, whether you’re running a marathon, completing a triathlon, or any other endurance event.

What is glycogen…and what on earth is super compensation?

Glycogen is the stored form of carbohydrates in animals, when we eat carbohydrate our bodies convert it and store it as glycogen, primarily in the muscles and liver. When we exercise our muscles use these stored carbohydrates as fuel, and the more fuel we have available at the start of exercise (or competition), the better able we are to reach and maintain high performance over an extended period of time.

Super-compensation is where the body functions above its normal capacity in response to a stress. In this case, it refers to the muscle's ability to store significantly more glycogen following exercise. At rest, our muscles will store roughly 1.5g glycogen per 100g of tissue, but following exercise they can store up to 4g per 100g, that’s roughly 2.7x more fuel! Better yet, this can be held at a “supra-normal” level for 3–5 days after the protocol (Gorforth 2003, Arnell 2007), which means that by using carb loading in the days leading up to a competition you would have almost 3x the potential stored energy to benefit your performance.

So how do we go about carbohydrate loading?

Let’s start with a brief history of carbohydrate super-compensation.

The initial protocols introduced by Bergström et al in the 1960’s required a glycogen depletion workout and 3 days of following a high carbohydrate, low fat and protein diet. This was further adapted to having 3 days of depletion workouts, 3 days of low-carb/high fat diet and a further 3 day depletion before 3 days of carbohydrate loading.

By the 1980s the glycogen depletion workouts had been phased out of recommendations, instead replaced with a 3-day exercise taper one week out from competition, followed by 2 days of light exercise and an off day whilst undertaking 3 days of carb loading (with 70% of calories from carbs) (Sherman 1981). This scheme represents a slightly easier and more competition friendly approach, by dropping the glycogen depletion phases of the initial 3-6 day protocols and can be modified further to start the load during the tapering period, to further reduce the timeframe (Burke et al 2000).

BUT! There is a caveat to all of this…TIME. It may not be very convenient or beneficial for an athlete to disrupt their training and taper their workload a week out from competition. Luckily, though, by the early 2000’s, it was established that you can effectively carb load to “supra-normal” levels of muscle glycogen in just one day!

This offered the advantage of not requiring a full week of tapering, and could be completed when most convenient for the athlete, as soon as the day before the event or several days out. Very useful if you need to account for rest or travel in the week leading into competition.

This is all great, but how do we do this?

No matter which protocol you follow, whether it’s 3 days, 6 days or 1, you will need to increase your carbohydrate intake to load up on glycogen and take advantage of the super-compensation effect. There are a few points you will have to consider:

How much?

The best way to judge how much you will need is to consider carbohydrate amounts relative to body weight — the science says anywhere from 10-12g per kg body weight is enough to load for most people, especially on the 1-day protocols.

So if you weigh 50kg, You would aim for 500-600g of carbohydrates during your load. That’s quite a bit, and leads into the next point:

What type?

With that amount of carbohydrate going into your system, you will want to make sure you are as comfortable as possible. Food volume becomes an important factor, by choosing sources high in fibre, this may result in gastrointestinal discomfort and distress, as well as being an absolute mission to get down. Luckily, the science suggests higher glycemic index carbs are the best option, allowing for rapid glycogen replenishment following your last training session, and limiting the food volume and potential discomfort of large, heavy food boluses.

Foods you may want to focus on include: white rice, potatoes, breads, pasta, fruits, dried fruits and cereals. Lean on the lower protein and fat varieties of common meals — no cheese or meat on a pizza, for example, or going for a lower fat sauce on your pasta. If you would like to indulge a bit and include some desserts or sweet treats, again aim for lower fat versions such as sorbet over ice cream (this would also limit the potential risk of distress from high dairy or fat intakes).

It may also be beneficial to consider liquids and supplements during this time, which can make it easier to spread out and get down than whole food sources. Carbohydrate drinks, gels, and bars are all practical options.

How do you time all of this?

Spread the food out over the course of the day. How you do it is quite individual, but by spreading it out, you will limit discomfort associated with large meals. This also gives yourself a bit of variety, as well as ensure your glycogen remains high and topped up as you move around through-out the day.

As an example, you could spread the carbohydrates out with 3 large meals, snacks, and drinks:

Breakfast:

Large bowl of cereal, Glass of orange juice, Banana, and berries (100g carbs).

Snack:

Rice cakes with Jam, dried mango, and an energy/carbohydrate sports drink (100g carbs).

Lunch:

Large bowl of Pasta in carrot and tomato sauce (100g carbs).

Snack:

Energy bar, Large Orange, Apple Juice. (80g carbs).

Dinner:

Jacket potatoes, tuna, low-fat mayonnaise, baked beans. Sorbet (120g carbs).

Other things to consider:

- The emphasis here is on carbohydrates, so protein and fat can take a back seat during the loading phase, aim to minimize them when possible — technically, keeping them to around 15% each of total calories means they won't limit your capacity to eat the necessary carbohydrates.

- Hydration is important. It’s REALLY essential during a carb load, as you will pull water into the muscles (3g water per gram of carbs) which can make you quite dehydrated — maintaining at least your normal intake is recommended and listen to your thirst, drink more if you feel you need it.

- Pick foods you tolerate well — this is not the time to introduce new foods, which may potentially upset your system.

- Do a “dry run” if you don’t have an established personalised plan so you can get an idea of what works (or what doesn’t!) before the event.

If you are competing in an endurance event soon and want evidence-based advice on how to prepare and eat on race day, contact me here on my website, or shoot me an email. If you have a competitive season coming up, you may want to consider my performance nutrition and competition services. Information can be found here: https://www.craigjoycecoaching.com/shop?Category=Sports%2520Services

References

BERGSTRÖM, J., & HULTMAN, E. (1966). Muscle Glycogen Synthesis after Exercise : an Enhancing Factor localized to the Muscle Cells in Man. Nature, 210(5033), 309–310. https://doi.org/10.1038/210309a0

Price, T. B., & Sanders, K. (2017). Muscle and liver glycogen utilization during prolonged lift and carry exercise: male and female responses. Physiological Reports, 5(4). https://doi.org/10.14814/phy2.13113

Gonzalez, J. T., Fuchs, C. J., Betts, J. A., & van Loon, L. J. C. (2016). Liver glycogen metabolism during and after prolonged endurance-type exercise. American Journal of Physiology-Endocrinology and Metabolism, 311(3), E543–E553. https://doi.org/10.1152/ajpendo.00232.2016

Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259. https://doi.org/10.1093/nutrit/nuy001

Mendes, M. P., Marinho, A. H., Moura, F. A., Bádue, G. S., Ferreira, G. A., de Araujo, G. G., Lima-Silva, A. E., & Ataide-Silva, T. (2025). Self-reported carbohydrate supercompensation and supplementation strategies adopted by Olympic triathlon athletes. Brazilian Journal of Medical and Biological Research, 58. https://doi.org/10.1590/1414-431X2024e14189

Danforth, W. H. (1965). Glycogen Synthetase Activity in Skeletal Muscle. Journal of Biological Chemistry, 240(2), 588–593. https://doi.org/10.1016/s0021-9258(17)45214-8

Hingst, J. R., Bruhn, L., Hansen, M. B., Rosschou, M. F., Birk, J. B., Fentz, J., Foretz, M., Viollet, B., Sakamoto, K., Færgeman, N. J., Havelund, J. F., Parker, B. L., James, D. E., Kiens, B., Richter, E. A., Jensen, J., & Wojtaszewski, J. F. P. (2018). Exercise-induced molecular mechanisms promoting glycogen supercompensation in human skeletal muscle. Molecular Metabolism, 16, 24–34. https://doi.org/10.1016/j.molmet.2018.07.001

Sedlock, D. A. (2008). The Latest on Carbohydrate Loading: A Practical Approach. In Curr. Sports Med. Rep (Vol. 7, Issue 4). www.acsm-csmr.org

Sherman, W. M., Costill, D. L., Fink, W. J., & Miller, J. M. (1981). Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. International Journal of Sports Medicine, 2(2), 114–118. https://doi.org/10.1055/s-2008-1034594

Burke, L. M., Hawley, J. A., Schabort, E. J., Clair Gibson, A. S., Mujika, I., Noakes, T. D., St Clair Gibson, A., & igo Mujika, I. (2000). Carbohydrate loading failed to improve 100-km cycling performance in a placebo-controlled trial. http://www.jap.org

Arnall, D. A., Nelson, A. G., Quigley, J., Lex, S., Dehart, T., & Fortune, P. (2007). Supercompensated glycogen loads persist 5 days in resting trained cyclists. European Journal of Applied Physiology, 99(3), 251–256. https://doi.org/10.1007/s00421-006-0340-4

Goforth, H. W., Laurent, D., Prusaczyk, W. K., Schneider, K. E., Falk Petersen, K., & Shulman, G. I. (2003). Effects of depletion exercise and light training on muscle glycogen supercompensation in men NIH Public Access. Am J Physiol Endocrinol Metab, 285(6), 1304–1311. https://doi.org/10.1152/ajpendo