Carbohydrate Loading - Tapering

Jan 23, 2025

By luis martinez mora

We often wonder what carbohydrate intake we should consume in the days leading up to a competition to ensure we have greater energy reserves during the event. And indeed, adopting short-term nutritional strategies to prepare for a race is very helpful. There's a lot of misinformation about this, and the question often arises:

What should we eat the week before to optimize our performance?

The answer is that what we eat the week before a competition won't help us on its own. We need to integrate it into a much broader nutritional plan . If we do it right, we can increase muscle glycogen stores by up to 50%, that is, from 300 to 400 grams.

Several protocols have been developed since it was discovered that performance could be enhanced with a carbohydrate loading phase prior to competition. These protocols share the same goal: to fully replenish the body's glycogen stores.

What is carbohydrate loading? What is the purpose of carbohydrate loading?

Before beginning with carbohydrate loading protocols, it's essential to understand what it is and its purpose. Carbohydrate loading, also known as tapering, is a nutritional strategy primarily used by athletes to maximize muscle glycogen levels before a competition or high-intensity sporting event.

It consists of deliberately increasing carbohydrate intake in the days leading up to the competition, in order to increase glycogen reserves in the muscles and liver.

Glycogen is the primary energy source during high-intensity exercise, so maintaining optimal reserves can improve athletic performance and delay muscle fatigue. Carbohydrate loading is typically phased, beginning several days before the event and involving a reduction in physical activity to promote glycogen storage.

Carbohydrates are the body's primary source of energy, and adequate fueling can improve endurance, strength, and recovery during prolonged exercise.

The Classic Model

It was in the 1960s that the first muscle biopsies began to be performed, allowing researchers to take samples of muscle tissue and study and measure the glycogen stored in the muscle tissue. (1) It was discovered that:

Glycogen concentration decreases during exercise, especially high-intensity exercise.
Higher concentrations of glycogen in the muscle resulted in less fatigue and better performance

From this point on, studies began to be done to see how muscle glycogen concentration could be increased and thus try to increase athletic performance.

One of these studies popularized the first carbohydrate loading protocol, the famous " Scandinavian diet ".

Protocol steps

Seven days before the competition, a very intense training session is undertaken to deplete glycogen stores. Then, for the next three days, carbohydrate intake is reduced to a minimum, followed by three days of very high carbohydrate intake.

With this carbohydrate loading protocol , it was observed that glycogen overcompensation was achieved, leaving the stores much fuller than if a moderate amount of carbohydrates were eaten every day. (1)

Disadvantages of this carbohydrate loading protocol

As Professor A. Jeukendrup tells us, this protocol presents some "little problems" that must be taken into account.

The first problem is that it involves extremely intense glycogen depletion training just 7 days before the competition. This training can leave you excessively fatigued or even with muscle soreness.

Similarly, by making such a strict restriction on carbohydrate intake during the 3 days following this glycogen depletion, the feeling of both physical and mental fatigue is very pronounced.

Restricting carbohydrate intake to maintain the necessary calorie intake necessitates a high-fat diet, which can cause significant gastrointestinal discomfort. Furthermore, to ensure supercompensation, it's recommended to stop training once glycogen stores are depleted through intensive training.

For many athletes who come from relatively high training volumes, having to stop abruptly 6 days before the competition represents a much greater sacrifice and punishment than dietary restrictions.

In general, although this protocol was highly effective, the side effects mentioned by Professor A. Jeukendrup may mean that these "minor problems" outweigh any benefits it may provide.

The Modified Model (2)

For this reason, in the eighties other slightly more conservative and moderate carbohydrate loading protocols began to be studied to minimize the negative effects, but still achieving good results.

In the new protocols, glycogen-depleting exercise was eliminated , and as training was reduced towards racing, carbohydrate intake was gradually increased.

Glycogen concentrations appear to be very high even after 6-7 days. Although glycogen loading did not reach levels as high as in the traditional protocol, race results were also good.

This carbohydrate loading protocol is based on following a normal nutritional plan without altering any macronutrient by adding or subtracting it, and then increasing carbohydrate intake by 8-12 gr/kg of weight for 3 days prior to competing.

Moderate protocol or 1 Day (3)

Studies conducted in the 1990s demonstrated that high-level, well-trained athletes could achieve similar muscle glycogen concentrations with just one or two days of carbohydrate loading and reduced training on those days. (In less well-trained athletes, this appeared to take a little longer.)

That's why it's very important that you don't increase your fat or protein intake in the days leading up to the competition and that you follow a nutritional plan tailored to your needs. It has been shown that increasing fat intake 7 days before the competition, along with a complete exclusion of carbohydrates, when loading 2-3 days before, doesn't result in as much muscle glycogen synthesis as the moderate or 1-day protocol .

As you can see in the chart, pre-competition nutritional guidelines below 8 grams of carbohydrate per kilogram of body weight are insufficient to obtain the maximum benefit from tapering or carbohydrate loading . Ensure you reach this minimum amount to achieve peak performance on race day.

On the other hand, all of this should be practiced in non-target competitions in order to test foods, digestion, tolerance, and load levels. This ensures that in the week leading up to a target competition, we don't try anything new and consume the maximum amount of carbohydrates tolerated per day, avoiding problems like osmotic diarrhea.

For shorter duration triathlons , such as the sprint distance, the 24-hour period before the triathlon will provide adequate time to normalize muscle glycogen stores and can usually be achieved with a high-CHO diet of at least 6g of CHO per kg of body weight during the 24 hours prior to race day (8).

For triathlons lasting longer than 90 minutes , glycogen supercompensation can be beneficial, and most well-trained or elite-level athletes can achieve this in the 36 to 48 hours prior to competition by increasing their dietary carbohydrate intake to approximately 10 to 12 grams of carbohydrate per kilogram of body weight. (9)

Final notes on carbohydrate loading protocols

To date, the Classical Model has been shown to have more disadvantages than advantages (including gastrointestinal problems, poor recovery, mood alterations, and risk of injury).

It is based on the principle of carbohydrate depletion/loading . There is a preliminary phase in which the subject is brought to a carbohydrate-deficient state by reducing intake by 90%, and a second phase in which a large carbohydrate load is provided, thus achieving a preventive response from the body consisting of supercompensation (an increase in muscle glycogen reserves).

On the other hand, the Modified Model is based on the classic one, with the difference that in the depletion phase the subject is administered only 50% less carbohydrates than were administered before the protocol

The pros and cons of carbohydrate loading

This protocol can improve performance by 2 to 3%, and endurance by up to 20%. However, this applies to activities lasting longer than 90 minutes. (2,4,5)
Each gram of carbohydrate is stored with 2.7-3 grams of water, meaning that 0.5 kg of carbohydrates results in a 2 kg weight gain. Therefore, it is necessary to assess whether it is preferable to gain weight or sacrifice glycogen reserves. (6)
It contributes to a better perception of fatigue and, therefore, better energy management throughout the competition. (7)

Therefore, as a general recommendation, carbohydrate loading should be performed when:

The competition is high intensity for 90 minutes or more.
The athlete's diet should be less than 7-8 g CHO/kg of body mass/day.
There are no medical contraindications, with special attention to diabetic athletes.