Can Delaying Eating Carbs Hurt Performance a Day Later?

In a recent randomized crossover trial, researchers looked at whether delaying eating carbs hurt performance, when participants performed high-intensity exercise the next day.

The Who, What and How

Researchers looked at 9 recreationally active young men, with an average age of 24. They examined a change in a gene associated with mitochondrial biogenesis (PGC-1α mRNA content). They also looked at mRNA and protein content of other genes associated with metabolism, HIIT capacity, muscle glycogen resynthesis, heart rate, and rate of perceived exertion (RPE), as well as blood lactate. This was all to find out if delaying eating carbs hurt performance a day later.

In this randomized crossover trial, participants did a high intensity interval training (HIIT) workout twice, completing 10 sets of 2 minutes of cycling at close to maximum power, with a minute rest between sets. 12 hours prior to the workout, all of the participants ate a standardized high carb diet. In a 3-hour timespan after the workout, the men were then either instructed to immediately eat carbohydrates (2.4 grams per kg of body weight) or a noncaloric, taste-matched placebo, which represented the delayed carb intake group. Total carb intake over the next 24 hours were the same between the two groups.

After the 24-hour recovery period, the participants again performed an HIIT workout, this time until exhaustion.

Prior to each bout of exercise, researchers recorded heart rate, RPE, an blood lactate, as well as after the 1st, the 5th, the 10th and the last interval. Muscle biopsies were also taken immediately before and after exercise, and three, eight and 24 hours after to look at glycogen, mRNA and protein content.

So, did delaying eating carbs hurt performance?

Researchers found that the men who delayed carbohydrate consumption post-exercise had impaired high-intensity exercise performance the next day, and those who ate carbs immediately after exercise performed better during their HIIT workout the next day, completing about four more intervals than those with the delayed consumption. Those with the delayed consumption performed worst. Immediate carbohydrate ingestion after exercise also led to a lower RPE on the 5th and 10th intervals.

Restricting carb intake after exercise can reduce muscle glycogen resynthesis,^[1] and inadequate muscle glycogen content can negatively affect performance in subsequent training sessions.^[2] Because of this, having adequate carbohydrate is better for endurance adaptations, because it essentially lets you do more work and sustain an elevated heartrate for a longer period of time.^[3]

Read the whole study here: https://pubmed.ncbi.nlm.nih.gov/39263899/

More Resources for Fueling for Training

• Pre-Workout Nutrition Course, taught by Kyla Channell, MSc
• Pre- Intra- and Post-Workout Recipe Book

References

1. Henriette Pilegaard, Takuya Osada, Lisbeth T Andersen, Jørn W Helge, Bengt Saltin, P Darrell NeuferSubstrate availability and transcriptional regulation of metabolic genes in human skeletal muscle during recovery from exerciseMetabolism.(2005 Aug)
2. Hearris MA, Hammond KM, Seaborne RA, Stocks B, Shepherd SO, Philp A, Sharples AP, Morton JP, Louis JBGraded reductions in preexercise muscle glycogen impair exercise capacity but do not augment skeletal muscle cell signaling: implications for CHO periodization.J Appl Physiol (1985).(2019 Jun 1)
3. Impey SG, Hearris MA, Hammond KM, Bartlett JD, Louis J, Close GL, Morton JPFuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis.Sports Med.(2018 May)

can delaying eating carbs hurt performance