Omitting carbohydrates from morning meals or even skipping whole breakfasts has become fashionable among many diet trends. You can read that protein ad fat breakfasts (i.e. without carbohydrates) are a way to maintain a good mood and concentration in people suffering from postprandial drowsiness, with glycemic disorders or a way of reducing body weight. The question is whether what is good and convenient for some will be just as good for others, for example for athletes?
Carbohydrates and physical performance in athletes
As you might expect, sports nutritionists consistently stick to a high-carbohydrate diet. This is due to the fact that carbohydrates are one of the main sources of energy for the body during exercise. What’s more, the demand for them increases with the intensity of the physical effort. Therefore, consuming them in the right amount and the right time can have a huge impact on exercise performance. . According to prof. Kerksick, who has been studying the impact of nutrition on the performance of athletes for years, the pre-workout meal is very important and should contain up to 4 g of carbohydrates per kg of body weight and be consumed 1-2 hours before training (Kerksick et al., 2017). The question is whether it is possible to combine both strategies – leaving out carbohydrates in the first part of the day (or even skipping the entire breakfast) and compensating for this with more carbohydrates at lunchtime?
The team of Prof. Metcalf set out to investigate a possible solution, in a study where 11 fit cyclists (VO2max: 61±5 ml/kg/min) underwent two time trials on a 20 km distance (Metcalfe et al., 2021). In the first case, the afternoon effort was preceded by both breakfast and lunch, and in the second case, only by a “fortified” lunch, so that the amount of carbohydrates was equal in both time trials. The average power output was demonstrated to be 3% (~9W) lower in the no-breakfast group.
The results of this study suggest that skipping breakfast (or carbs in breakfast) can negatively impact performance in the later part of the day, even when we manage to catch up on carbs later on that day. Consumption of carbohydrates well in advance of training may affect the amount of muscle glycogen, the synthesis of which takes many hours. The longer you exercise, the more important the glycogen stores are.
Summary
In conclusion, consuming carbohydrates before workout can help improve performance during prolonged, high-intensity exercise. However, in the case of long and very intense workouts, a single pre-exercise meal may not be enough to maximize the athlete’s physical performance.

Bibliography
Kerksick, C. M., Arent, S., Schoenfeld, B. J., Stout, J. R., Campbell, B., Wilborn, C. D., Taylor, L., Kalman, D., Smith-Ryan, A. E., Kreider, R. B., Willoughby, D., Arciero, P. J., VanDusseldorp, T. A., Ormsbee, M. J., Wildman, R., Greenwood, M., Ziegenfuss, T. N., Aragon, A. A., & Antonio, J. (2017). International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition 2017 14:1, 14(1), 1–21.
Metcalfe, R. S., Thomas, M., Lamb, C., & Chowdhury, E. A. (2021). Omission of a carbohydrate-rich breakfast impairs evening endurance exercise performance despite complete dietary compensation at lunch. European Journal of Sport Science, 21(7), 1–22.