Carb Loading: When It Works and When It Doesn't
TL;DR — Carb loading only works for efforts lasting approximately 90 minutes to two hours. Shorter than that? Then it's unnecessary, as your internal reserves are sufficient. In the one to two days leading up to it, aim for 8 to 10 grams of carbohydrates per kilogram of body weight per day, eat low-fat and low-fiber foods, and train gently. Loading does not replace refueling during the effort itself. My fuel plan tool calculates your loading based on your weight.
Carb loading is one of the most misunderstood parts of a fuel plan. Many athletes do it out of habit before every race, even if it's too short to benefit. Others skip it when it could make all the difference. In the complete guide to fueling for cycling, loading is part of the bigger picture. Here, I explain when it works, when it doesn't, and how much you need.
What carb loading actually does
Your muscles and liver store carbohydrates as glycogen, your internal sugar reserve. This reserve is limited. With carb loading, you consciously eat more carbohydrates in the days leading up to a long effort, so that this reserve is maximally filled at the start. The effect: you can rely on your own reserves longer before you need to refuel, and you postpone the moment you run out of energy.
The 90-minute limit
This is where it often goes wrong. For efforts shorter than approximately 90 minutes to two hours, loading is pointless. Your normal reserves are already more than enough to cover the entire effort. Extra loading yields nothing but a full and heavy feeling at the start. Only for longer endurance efforts, a long ride, a half or full marathon, a triathlon, does loading become useful. There, a full reserve can save you from the dreaded slump in the final part.
How much: calculate based on your weight
The guideline for loading is expressed per kilogram of body weight. In the one to two days before a long race, aim for about 8 to 10 grams of carbohydrates per kilo per day. For an athlete weighing 70 kilos, this amounts to 560 to 700 grams of carbohydrates per day. That's a lot, and you won't achieve it with an extra plate of pasta alone. It requires a conscious shift of your entire day towards carbohydrate-rich, easily digestible foods.
Important here: reduce your fat and fiber intake on those days and keep your training gentle. Fiber and fat fill your stomach without replenishing much glycogen, and rest ensures that you don't immediately use up the stored reserve. My fuel plan tool automatically calculates your loading number once you enter your weight and race.
What to load with
Loading is precisely the time for ordinary food. White pasta, white rice, white bread, oatmeal, ripe bananas, potatoes, pancakes. Fast, easily digestible carbohydrates without much fiber. This is not the time for my fruit performance bars: they are fuel during exercise, not a way to stack hundreds of grams at the kitchen table. Honestly, and it saves you money.
| Effort | Carb loading needed? |
|---|---|
| Under 90 minutes | No, reserves are sufficient |
| 90 min to 2 hours | Light loading can help |
| Long race, 2 hours plus | Yes, 8 to 10 g/kg/day |
Loading is the beginning, not the whole plan
A full reserve at the start is powerful, but it runs out. During a long effort, you must continue to refuel, because even a maximal load does not cover three, four, or five hours. Loading and refueling during the effort work together. If you want to know how much you need along the way, read how to distribute your bar and gel during your effort. No guesswork. Fuel. Fuel your flight.
The science
The role of glycogen stores in performance and the dosage of carbohydrate intake are established in controlled research on carbohydrate metabolism during prolonged exercise. King and colleagues (2019) substantiate the relationship between carbohydrate dose, glycogen metabolism, and performance.
References
King AJ et al. Liver and muscle glycogen oxidation and performance with dose variation of glucose-fructose ingestion during prolonged exercise. Eur J Appl Physiol 2019. doi:10.1007/s00421-019-04106-9
Frequently Asked Questions
From what duration is carb loading useful?
From approximately 90 minutes to two hours of effort. Shorter than that, your body has enough of its own reserves, and loading adds nothing.
How many carbohydrates per day during loading?
About 8 to 10 grams per kilo of body weight per day, in the one to two days before the race.
Should I stop training during loading?
Don't stop, but temper it. Gentle training ensures that you don't immediately use up the stored reserves.
Can I carb load with energy bars?
That is not the intention. You load with ordinary, carbohydrate-rich foods such as pasta and rice. Bars are fuel during the effort itself.
Does carb loading replace eating during exercise?
No. A full reserve runs out during long efforts. You must continue to refuel along the way.
