Fasted Workout - Good Or Bad?
21/4/2019
Written By: Ryan Chan |
|
Fasted workout generally means that a person working out without prior consumption of food. More specifically, on an empty stomach as compared to the usual fed state. Working out in a fasted state have gained its popularity when it is marketed to help you lose weight, especially body fats.
Today, we will compare fasted state workout to fed state workout with regards to general weight management and the development of muscles.
Today, we will compare fasted state workout to fed state workout with regards to general weight management and the development of muscles.
So what’s the theory behind Fasted Workout?
Our body generally prefer using carbohydrates, which comes from our food, as the fuel source for physical activity, more specifically glucose. The excess glucose that is not being use during our daily activities gets stored within our liver and muscles as glycogen for future use. This storage space is commonly known as the glycogen storage.
When we are in a fasted state, our glycogen storage will naturally be low due to the lack of food consumption. Tapping on this fact, working out during this period will then help to draw out the next best resource for fuel, your fats. Thus this is where the benefit of losing more body fats during fasted workout comes from.
At least that is what is in theory.
When we are in a fasted state, our glycogen storage will naturally be low due to the lack of food consumption. Tapping on this fact, working out during this period will then help to draw out the next best resource for fuel, your fats. Thus this is where the benefit of losing more body fats during fasted workout comes from.
At least that is what is in theory.
How our body prioritize which fuel to use?
During physical activity, our body primarily uses carbohydrates first due to the lack of oxygen intake to metabolise the fats as fuel. This is also the main reason why there is a difference between the type of fuel source used during aerobic and anaerobic exercises where there is a drastic difference when it comes to oxygen intake within our body.
During aerobic exercises such as brisk walking and jogging, our heartrate increases steadily and is sustained at a longer period of time, resulting in more oxygen intake into our body. This increase in oxygen intake tagged with the low-to-moderate intensity of aerobic exercises allows our body to burn more fats than carbohydrates for fuel. As such, our body generally burns around 60-80% fats and 20-40% carbohydrates during aerobic exercises.
On the other hand, during anaerobic exercises such as weight lifting and sprinting, our muscles require an immediate source of energy for work thus drawing mostly the glucose from the glycogen storage for fuel and producing lactic as a by-product during the process. As such, our body generally burns around 60-80% carbohydrates and 20-40% fats for fuel during anaerobic exercises.
However, you might have notice by now that we seem to be forgetting another possible fuel source – Protein. Protein in this case are your muscles, where during time of emergency, gets broken down to fuel your activity. It is your body’s least favorite fuel source and the one that you pray not to be broken down and wasted.
So in this case, when is the time of emergency?
When your glycogen storage is empty.
Let’s have a look now at the comparison between Fasted State Workout and Fed State Workout.
During aerobic exercises such as brisk walking and jogging, our heartrate increases steadily and is sustained at a longer period of time, resulting in more oxygen intake into our body. This increase in oxygen intake tagged with the low-to-moderate intensity of aerobic exercises allows our body to burn more fats than carbohydrates for fuel. As such, our body generally burns around 60-80% fats and 20-40% carbohydrates during aerobic exercises.
On the other hand, during anaerobic exercises such as weight lifting and sprinting, our muscles require an immediate source of energy for work thus drawing mostly the glucose from the glycogen storage for fuel and producing lactic as a by-product during the process. As such, our body generally burns around 60-80% carbohydrates and 20-40% fats for fuel during anaerobic exercises.
However, you might have notice by now that we seem to be forgetting another possible fuel source – Protein. Protein in this case are your muscles, where during time of emergency, gets broken down to fuel your activity. It is your body’s least favorite fuel source and the one that you pray not to be broken down and wasted.
So in this case, when is the time of emergency?
When your glycogen storage is empty.
Let’s have a look now at the comparison between Fasted State Workout and Fed State Workout.
Fasted State Workout VS Fed State Workout
Aerobic Exercise
Eg. Jogging, Swimming, Cycling, Elliptical etc.
Fasted State: Due to the fuel source and energy system used for aerobic exercise, working out in a fasted state during this type of exercise enhances the fat burning effect, drawing out more fats as fuel more efficiently. However, it is also worth noting that during any form of exercise, both fats and carbohydrates will always be used simultaneously. Thus under prolong moderate intensity aerobic exercise duration, where your glycogen storage is low to begin with, there will be a high chance where your body will turn to protein for energy due to the lack of glucose, resulting in the loss of muscle mass. Thus, it is recommended to keep aerobic workout during fasted state to less than 30 minutes. But do note that this duration is highly subjective to the intensity level of your aerobic exercise. The higher the intensity, the shorter the duration should be to prevent the loss of muscle mass. More explanation regarding workout duration can be found here.
Fed State: As compared to fasted state, it is true that our body will not be able to draw out the fats as effectively as fasted state during the workout. However, one can definitely benefit more from being able to sustain a longer and more intense aerobic workout with less risk of muscle wastage. Looking at it from this perspective, the total calories output will definitely increase coming from a longer and more intense fed state workout and this might in terms lead to a bigger calories deficit for weight management, drawing deeper into the body’s storage fuel for the body to continue functioning.
Eg. Jogging, Swimming, Cycling, Elliptical etc.
Fasted State: Due to the fuel source and energy system used for aerobic exercise, working out in a fasted state during this type of exercise enhances the fat burning effect, drawing out more fats as fuel more efficiently. However, it is also worth noting that during any form of exercise, both fats and carbohydrates will always be used simultaneously. Thus under prolong moderate intensity aerobic exercise duration, where your glycogen storage is low to begin with, there will be a high chance where your body will turn to protein for energy due to the lack of glucose, resulting in the loss of muscle mass. Thus, it is recommended to keep aerobic workout during fasted state to less than 30 minutes. But do note that this duration is highly subjective to the intensity level of your aerobic exercise. The higher the intensity, the shorter the duration should be to prevent the loss of muscle mass. More explanation regarding workout duration can be found here.
Fed State: As compared to fasted state, it is true that our body will not be able to draw out the fats as effectively as fasted state during the workout. However, one can definitely benefit more from being able to sustain a longer and more intense aerobic workout with less risk of muscle wastage. Looking at it from this perspective, the total calories output will definitely increase coming from a longer and more intense fed state workout and this might in terms lead to a bigger calories deficit for weight management, drawing deeper into the body’s storage fuel for the body to continue functioning.
Anaerobic Exercise
Eg. Weight Training, Sprinting, High Jump etc.
Fasted State: The lack of glucose within your glycogen storage will drastically affect your performance, especially on your strength and energy level. To compensate with the lack of ideal fuel source, your body will turn to break down your muscles for fuel to sustain your anaerobic workout. In this situation, ironically, you are training to develop more muscles but in the process, you are burning them to fuel your training. The lack of energy might also result in the lack of focus, increasing the chance of possible injuries. Thus, it is not recommended to participate in anaerobic workout during fasted state.
Fed State: During fed state where your body’s glycogen storage is generally high, one might benefit better from being able to push through an intense anaerobic workout, such as lifting heavier weights and sprinting uphill, to achieve greater long term result such as building more lean muscle mass which will result in higher metabolic rate, as compared to a temporary increase in the utilization of fats during one fasted state workout.
Eg. Weight Training, Sprinting, High Jump etc.
Fasted State: The lack of glucose within your glycogen storage will drastically affect your performance, especially on your strength and energy level. To compensate with the lack of ideal fuel source, your body will turn to break down your muscles for fuel to sustain your anaerobic workout. In this situation, ironically, you are training to develop more muscles but in the process, you are burning them to fuel your training. The lack of energy might also result in the lack of focus, increasing the chance of possible injuries. Thus, it is not recommended to participate in anaerobic workout during fasted state.
Fed State: During fed state where your body’s glycogen storage is generally high, one might benefit better from being able to push through an intense anaerobic workout, such as lifting heavier weights and sprinting uphill, to achieve greater long term result such as building more lean muscle mass which will result in higher metabolic rate, as compared to a temporary increase in the utilization of fats during one fasted state workout.
2 Bonus Points – Probably the nail in the coffin
By now you should have a sense that a fasted workout will definitely be less intense and less muscle sparring that a fed one.
So why is intensity so important other than burning more calories during a workout?
It is because of the Excess Post-Exercise Oxygen (EPOC). The higher your workout intensity is, the greater the EPOC will be. EPOC is the phase where your body uses oxygen to restore muscle glycogen and rebuild muscle proteins damaged during exercise. Research have shown that you can burn up to 75 calories more an hour or 33% more calories in general, 16 to 36 hours after workout. To make things even better, 80% of the calories burn during EPOC are actually from fats. Thus a low intensity workout coming from being in a fasted state will create little to almost no EPOC effect. Meaning, there will be little to no post workout fat burning effect. This itself will definitely offset the different in terms of the amount of fats burnt during a single workout between a fasted and a fed state. This effect is also similar comparing strength training to steady-state cardio as mentioned in this article.
And to end things off, one of the biggest red flag when participating in any workout is not to lose muscle mass. However, researches have shown that working out during a fasted state resulted in more than twice the amount of muscle loss as compared to a fed state workout. On top of that, there were less muscle development to aid in the increase of overall metabolic rate.
Here’s a simple example
Person A did fasted state cardio for 30 minutes and burnt 200 calories. Of which, 170 calories (85% fats – more sensitive) come from fats which equal to about 19 grams of fats.
On the other hand, Person B did a 30 minutes HIIT workout under a fed state and burnt 350 Cal. Of which, 70 calories (20% fats) come from fats which equal to about 8 grams of fats. Over a 24 hours period, his body undergo the EPOC effect, burning 16% (humble estimation) more calories throughout the day. That equals to an additional 288 calories (taking total calories a day as 1800 calories) or 32 grams of fats burnt, bringing the grand total of fats burnt to 40 grams.
Thought Person A burnt more fats during his workout, Person B clocked in more calories burnt during his workout and burnt more fats throughout the day. On top of that, we have not taken into account of the possible muscle development for Person B which will increase his metabolism leading to an increase in overall calories burnt.
So why is intensity so important other than burning more calories during a workout?
It is because of the Excess Post-Exercise Oxygen (EPOC). The higher your workout intensity is, the greater the EPOC will be. EPOC is the phase where your body uses oxygen to restore muscle glycogen and rebuild muscle proteins damaged during exercise. Research have shown that you can burn up to 75 calories more an hour or 33% more calories in general, 16 to 36 hours after workout. To make things even better, 80% of the calories burn during EPOC are actually from fats. Thus a low intensity workout coming from being in a fasted state will create little to almost no EPOC effect. Meaning, there will be little to no post workout fat burning effect. This itself will definitely offset the different in terms of the amount of fats burnt during a single workout between a fasted and a fed state. This effect is also similar comparing strength training to steady-state cardio as mentioned in this article.
And to end things off, one of the biggest red flag when participating in any workout is not to lose muscle mass. However, researches have shown that working out during a fasted state resulted in more than twice the amount of muscle loss as compared to a fed state workout. On top of that, there were less muscle development to aid in the increase of overall metabolic rate.
Here’s a simple example
Person A did fasted state cardio for 30 minutes and burnt 200 calories. Of which, 170 calories (85% fats – more sensitive) come from fats which equal to about 19 grams of fats.
On the other hand, Person B did a 30 minutes HIIT workout under a fed state and burnt 350 Cal. Of which, 70 calories (20% fats) come from fats which equal to about 8 grams of fats. Over a 24 hours period, his body undergo the EPOC effect, burning 16% (humble estimation) more calories throughout the day. That equals to an additional 288 calories (taking total calories a day as 1800 calories) or 32 grams of fats burnt, bringing the grand total of fats burnt to 40 grams.
Thought Person A burnt more fats during his workout, Person B clocked in more calories burnt during his workout and burnt more fats throughout the day. On top of that, we have not taken into account of the possible muscle development for Person B which will increase his metabolism leading to an increase in overall calories burnt.
Conclusion
It is not right to say that working out in a fasted state is good or bad. Rather, there are things to take note of if you wish to work out during a fasted state such as keeping the workout intensity low and shortening the duration of your workout to prevent muscle loss. At the same time, fasted state workout is especially useful for people who faces problem with insulin resistance as it has greater impact in improving insulin sensitivity due to the optimal amount of glucose within the body during the workout.
However, apart from simply focusing on burning more fats during a workout, one should look at a more sustainable long term strategy in reducing body fats and managing weight. This includes burning more calories to create greater caloric deficit as well as building muscle to increase metabolism. In this case, a fed state workout will be more recommended.
However, apart from simply focusing on burning more fats during a workout, one should look at a more sustainable long term strategy in reducing body fats and managing weight. This includes burning more calories to create greater caloric deficit as well as building muscle to increase metabolism. In this case, a fed state workout will be more recommended.
Articles You Might Be Interested