What is Fasting Aerobic Exercise?
Fasting aerobic exercise refers to performing cardiovascular activities, like running or cycling, after a period of fasting, usually overnight. In this state, the body lacks immediate energy from food, which encourages it to use stored fat as fuel.
The science behind fasting aerobic is based on the body’s metabolic response:
- Post-Meal Exercise: The body uses carbohydrates from recent meals as its primary energy source.
- Fasted Exercise: In the absence of carbohydrates, the body shifts to burning fat for energy.
While this sounds like an ideal fat-loss strategy, the reality is more nuanced.
Basic Metabolic “Truths”
- Consuming a meal or snack before exercise essentially provides the body with nutrients, specifically carbohydrates, proteins, and fats (depending on the composition of the meal).
- During aerobic exercise, depending on its intensity, the body utilizes these components at different rates to generate energy for exercise. Specifically, in the case of aerobic exercise such as running, the preferred energy source for the body is the carbohydrates in the bloodstream (sugar) and the stored carbohydrates in the body (glycogen).
- It has been shown that when these carbohydrates are provided exogenously before exercise (i.e., by consuming a meal), the body prefers to use them as an energy source over stored fat. This is particularly evident during low or moderate-intensity exercise (where oxygen consumption is below 75% of maximum oxygen consumption – VO2 max).
- On the other hand, for the same intensity of exercise and in a fasted state (absence of carbohydrates), the body turns to body fat as a “fuel” for exercise.
So far, everything indicates that exercising in a fasted state leads to higher utilization of stored fat as an energy source for exercise.
It is important to note that this metabolic adaptation (i.e., increased fat utilization during exercise in a fasted state) is mainly characteristic of less-trained individuals. Conversely, trained individuals continue to derive significant energy from stored body fat, even if they have consumed a carbohydrate-containing meal before exercise.
Fasting Aerobic Exercise and Long-Term Weight Loss
Although studies in this specific area are limited, whether or not a meal is consumed before exercise does not seem to significantly affect overall daily calorie expenditure or long-term weight loss.
In other words,
There doesn’t seem to be any advantage in long-term fat loss when exercise is performed in a fasted state compared to exercising after consuming a meal.
Moreover, it is worth mentioning that the above metabolic adaptation does not seem to confer any advantage (or disadvantage) regarding the preservation of muscle mass, whether an individual is in a fasted state or not.
Performance and Fasting Aerobic: Does It Impact Your Workout?
Given that fat loss is not the sole goal of exercise, it is important to examine how food consumption affects exercise performance and the preservation of muscle tissue. A sustainable weight loss plan should incorporate a balanced diet that may include weight loss supplements for Women for added convenience, along with regular exercise.
Regarding the first aspect, current data indicates that the performance of moderate-intensity exercise is not significantly affected by whether a meal has been consumed beforehand or not. However, this does not hold for high-intensity exercise (near VO2 max), where consuming carbohydrates before the meal provides greater assistance in performance compared to exercising in a fasted state.
As for the preservation of muscle mass, relevant studies do not reveal any advantages or disadvantages based on whether an individual is in a fasted state or not.
What you should remember:
- Performing aerobic exercise in a fasted state leads to higher utilization of stored fat as an energy source (thus potentially greater fat loss) during exercise.
- However, there appears to be no difference in long-term weight or fat loss whether exercise is performed after consuming a meal or not.
- In cases of high-intensity exercise (near VO2 max), consuming a meal beforehand may improve performance.
The Bottom Line on Fasted Aerobic Exercise
When it comes to weight loss and fat loss, there doesn’t appear to be a significant advantage to exercising in a fasted state compared to consuming a meal beforehand. The utilization of stored fat as an energy source during exercise is influenced by factors such as exercise intensity and an individual’s training level. Ultimately, what matters most is finding an exercise routine that works for you and supports your long-term fitness goals.
