In this article, we will look at a comparison of two training approaches, the so-called fasted and the post-meal or "fed" approach, and specifically in relation to endurance activity and running in particular.
Many of us have heard that the best form of weight loss is fasted cardio training. This claim is often based on the fact that reduced glucose and insulin levels lead to increased activity of the enzyme hormone-sensitive lipase, which is heavily involved in the breakdown of fats, and thus our body uses fat as the dominant source of energy. Many of the studies conducted so far confirm this claim, but it is necessary to look at the whole issue from a slightly broader perspective. It also shows, for example, that if the utilization of fats is increased during physical activity, the utilization of carbohydrates is enhanced during the rest of the day.
At the same time, if a training session is preceded by the consumption of a meal, the energy expenditure in the following training session may be increased to some extent. Several studies have directly compared the "fed" and "fasted" approaches in terms of weight loss. However, significant differences in weight loss have not been demonstrated and similarly for the active body mass parameter, i.e. muscle mass.
If we look at the comparison through the lens of athletic performance (especially endurance), there were also no significant advantages found for the "fasted" approach. It appears that, especially at lower intensities, neither approach significantly affects athletic performance, however, in some cases the "fed" approach was found to be preferable. This is the case, for example, in endurance activities lasting longer than 60 minutes or in high-intensity exercise - in these cases, fasting carries increased risks, especially those associated with hypoglycaemia (exhaustion, weakness, impaired performance, etc.).
This is where low glycogen levels prove to be a problem, and it could be even more of a complication in the case of multi-phase training, where insufficient glycogen stores can significantly limit physical performance. In fact, carbohydrates are one of the most ergogenic components of the diet and physical performance (especially of a high-intensity endurance nature) may be limited when they are deficient.
Therefore, fasted running is definitely not the only and best option for weight loss. More important than when we eat is what we eat and what our overall daily energy balance is. So again and again - CALORIC DEFICIT is essential for weight loss! Similarly, fasted running has not been shown to have significant positives in relation to athletic performance, on the contrary, in certain cases it may have more negative benefits.
We should therefore first and foremost focus on our own feelings, the quality of our performance and simply choose the option where we feel more comfortable. Much more important than worrying about whether to train before or after breakfast is to get up and get going in the first place!
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