89. DOES THE FREQUENCY OF CARBS INGESTION DURING RACES MATTER?

Photo by Stefan Scheepmaker on Unsplash

In the previous KisW Research Notes, we saw a lot about the importance of carbohydrates for long duration cycling performance.

Carbohydrates are stored in the body mainly as muscle and liver glycogen. While fat is a virtually unlimited resource, unfortunately, glycogen is not. For example (1), a 70kg man with 10% of body fat have stored approximately:

• 2400 kcal as muscle glycogen

• 375 kcal as liver glycogen

• 68000 kcal as fat

.

Data from Maunder et al. (1)

Depletion of glycogen is linked to fatigue. For example, low muscle glycogen levels seems to disrupt the ionic mechanisms that permits muscle contraction (calcium release, sodium and potassium regulation).

So, how to maintain sufficient/optimal glycogen levels during exercise? Theoretically there could be three ways:

1. Increase the capacity to burn more fats at specific exercise intensities.

2. Optimize starting glycogen level through diet and recovery

3. Oxidizing more exogenous (ingested during exercise) carbs

The last point is the rational behind all the ‘Carbolution’ that occurred within the cycling world in the last 5-10 years, which has led pro road cyclists to ingest more and more carbs during races (even >120 g/h during the longest and hardest stages).

About carbs ingestion during races to optimize performance, we have seen the following points:

1. The Total Amount Ingested

   90 grams per hour seems to be the optimal amount to maximise performance. Studies that investigated 110-120 grams per hour did not find any positive additional effects on performance (2) or glycogen sparing (3) when compared to 90 g/h. However, these studies have been conducted on trained but not professional athletes. Future studies can verify if similar results are obtained on pro cyclists, or higher than 90 g/h can boost world-class athletes’ performance, given that they have a higher energy expenditure and consume more carbs during races when compared to lower level athletes.

2. The Type of Carbs Ingested:

   • When you target below ~60 g/h or lower: you can just don’t care about the type of carbs you ingest (glucose vs fructose). You should be able to absorb everything.

   • Between ~60 and ~90 g/h: glucose to fructose ratio of 2:1 should be used. In this way you are adding fructose while being sure to no exceed 60 grams per hour of glucose, which seems to be the average saturation level of gastrointestinal glucose transporters.

   • When going over ~90 g/h:

     You should increase the ratio of fructose ingested, so a glucose to fructose ratio of 1:0.8 or even 1:1 (if total carbs amount is higher than 120 g/h) should be used to not go over ~60 grams per hour of glucose and so to avoid overdosing gastrointestinal glucose transporters.

   • Note that this threshold value (~60 g/h) could depend also on your body size (read more here).

3. Body Size:

   Larger athletes can oxidise (use to produce energy) more exogenous carbs during exercise than smaller ones, both at the same relative and absolute intensity.

   Body size explains 35-40% of the differences in exogenous carbs oxidation during exercise between different individuals. This is why we put the symbol ‘~’ in the above suggested amounts of carbs. In addition to body size, some level of variability between different athletes in the ability to absorb and use exogenous carbs during exercise can be related to different levels of gut glucose transporters between different individuals, which might be increased through gut training.

4. The form of carbohydrates ingested during exercise (solid vs gel vs fluid):

   This doesn’t affect exogenous carbs utilisation (how much of the carbs ingested the body uses to produce energy) or performance. So, you can choose the form that you like the most. Of course, you should also consider the logistics and feasibility of a feeding strategy in a certain moment of race. It is not easy to eat a sandwich when an opponent is attacking.

An additional fifth parameter that would be interesting to understand is whether even the frequency of carbohydrates ingestion during the race matters.

When the total amount ingested is the same, does the frequency of carbs ingestion during exercise influence performance, glycogen sparing and gastrointestinal symptoms?

A hot off the press (2025) study published on European Journal of Sport Science by Jones and Colleagues (Liverpool John Moores University, UK) tried to answer this question. (1)

---

WHAT DID THEY DO?

• 20 recreationally active males (~ 24 years old, ~ 50 VO2max) participated in this study.

• The cycled for 3 hours at first lactate threshold (139 ± 29 W) on two different days and conditions:

  1. HIGH FREQUENCY CARBS (HFC): consuming 90 g/h of carbs as 22.5 g every 15 min.

  2. LOW FREQUENCY CARBS (LFC): consuming 90 g/h of carbs as 45 g every 30 min.

  You can see that the total amount of carbohydrates ingested was the same (90 g/h), with the only difference being the frequency of their ingestion.

• Following the 3 hours at first threshold, they performed a time to exhaustion cycling trial at an intensity corresponding to 150% of the first threshold (209 ± 43 W), which should correspond to an intensity above the second threshold/FTP.

---

WHAT DID THEY FIND?