For a long time, there has been a debate about which is the ideal fuel for the body: fats or carbohydrates? The reality is that there is no need to choose one over the other, since our body is capable of using both efficiently according to the demands of the activity performed. This ability is known as metabolic flexibility.
When to use carbohydrates or fats?
The body uses different metabolic processes to generate energy, and the choice of fuel depends mainly on the intensity and duration of the effort. For example, during high-intensity activities—such as weight lifting or explosive training—the use of carbohydrates is preferred. In these situations, the body activates anaerobic glycolysis, which quickly transforms stored glycogen into ATP, allowing an immediate supply of energy.
In contrast, during low- to moderate-intensity exercise, such as walking or jogging at a steady pace, the body mainly uses fat. The oxidation of these lipids occurs in aerobic metabolism, a slower but highly efficient process for providing sustained energy. This pathway favors the use of lipid reserves and contributes to improving metabolic health.
Metabolic processes: aerobic and anaerobic
The body has two main routes for ATP production:
- Aerobic Metabolism: It uses oxygen to break down fats and generate energy. This is the ideal process for lower intensity and longer duration activities, as it allows for a continuous supply of ATP.
- Anaerobic Metabolism: It does not depend on oxygen and is based on the rapid conversion of carbohydrates to obtain ATP. This process is crucial during intense efforts, although the amount of energy produced is lower compared to aerobic metabolism.
Strategies to enhance metabolic flexibility
The key to optimizing physical performance and overall health is to train the body to optimally utilize both fuels. This can be achieved by structuring the training routine and nutrition to suit the specific demands of each type of activity.
High intensity days
During days dedicated to high-intensity training, such as strength training, the body needs an energy source that responds immediately. During these workouts, it is essential to increase carbohydrate intake before and after the activity. This approach not only ensures a rapid supply of energy, but also stimulates cellular pathways, such as the mTOR pathway, that promote protein synthesis and muscle development. The goal on these days is clear: maximize performance and meet the energy demands of short, powerful efforts.
Low intensity days
In contrast, on days dedicated to low- to moderate-intensity aerobic exercise, such as long walks, it is recommended to maintain a moderate or low carbohydrate intake. This strategy encourages the body to use fat as its main source of energy, activating metabolic pathways such as AMPK, which enhance lipid oxidation and improve metabolic health. In this way, the body develops a greater capacity to burn fat efficiently, which promotes both recovery and a healthier body composition.
Conclusion
The debate over which fuel is “better” fades away when you understand that your body adapts and uses both carbohydrates and fats based on the specific needs of each activity. The real strategy lies in training metabolic flexibility: enhancing carbohydrate use for intense efforts and favoring fat oxidation during lower intensity activities. This balanced approach not only improves physical performance, but also contributes to better health and optimal body composition in the long term.