If you’re a gym rat by any means, you’ve likely heard of fasted cardio. However, it’s a widely debated topic among researchers, individuals, and fitness experts.
Does fasted cardio actually work? Does it help you burn fat faster? What are the benefits of fasted cardio?
Below I explore how fasted cardio works, what the benefits of fasted cardio are, and how you can incorporate fasted cardio into your workout routine.
What is Fasted Cardio?
Fasted cardio is cardio activity performed after not eating for at least 4-8 hours. Most people do it in the morning but it can be done anytime.
The main benefits of fasted cardio include weight loss, priming your body for optimal nutrient absorption, and an increase in insulin sensitivity which I’ll cover in more detail below.
How does it work?
It really comes down to one thing: insulin. Insulin is a hormone made by the pancreas that’s responsible for controlling your blood sugar levels. Insulin shoots up anytime you eat and helps convert the sugar in your blood into energy for immediate use or into fat for future use.
So when you exercise first thing in the morning before eating, your insulin levels are low. This means you’ll burn fat easier and faster because your body doesn’t have to worry about depleting your blood sugar levels before burning the fat stored in your liver and muscles.
What is glucagon?
On the other hand, glucagon is released when blood sugar levels are low. Glucagon is a hormone that:
- Breaks down fat stores into usable fatty acids for energy
- Stimulates the body to create glucose from amino acids
- And activates the breakdown of glycogen in the liver.
Insulin and glucagon work together to control your blood sugar levels, as well as direct where your energy comes from.
For a more detailed breakdown of how insulin and glucagon work and how it’s linked to burning fat, check out this video:
What are the Benefits of Fasted Cardio?
While most fitness experts agree that fasted cardio has its benefits, the studies are mixed.
A study in 2014 compared a fasted cardio group and a fed cardio group. The fasted cardio group performed their workout after fasting overnight. The fed cardio group consumed a meal before their workout. Researchers found next to no difference between the 2 groups and noted similar fat-loss benefits.
A 2016 study in the Journal of Nutrition and Metabolism had a similar experimental set-up. Yet, it produced different results. Researchers found that fasted cardio decreased individual’s’ energy intake over the next 24 hours and increased their fat burn.
So, what’s the truth? Who should you believe? It really comes down to your diet, your fitness level, and your fitness goals. Fasted cardio could potentially leave you feeling sluggish and on edge during your workout, especially if you’re new to exercise.
If this is the case, a small pre-workout meal may provide immense benefits for you. It could give you that extra push to amp up the intensity of your workout, meeting your desired fitness goals. Go for something light, like a banana or piece of toast.
However, fasted cardio has many benefits, especially if weight loss is your ultimate goal. Here are the 3 main benefits you’ll find if you decide to start doing cardio on an empty stomach.
1. Helps Burn Fat
As mentioned above, fasted cardio ups your fat burn since blood sugar and insulin levels are low after a 4-8 hour fast.
Yet if your goal is to build muscle, fasted cardio isn’t for you. Fasted cardio breaks down fat stores but may also use amino acids to fuel your body. Why does this matter?
If you want to build muscle, you need amino acids to build protein and muscle tissue. If there aren’t any amino acids, you won’t build muscle. Hence, nutritional supplement products containing amino acids, such as Optimum Nutrition Micronized Creatine Monohydrate Powder.
This is where diet comes into play. You can up your amino acid and protein intake to reduce these effects. For more on this, check out my article on does cardio kill gains.
In addition, the body is complex. What works for one person may not work for you. Go with what feels good for you, your body, and your fitness goals.
2. Optimal Nutrient Absorption
In a fasted state, your body is primed for optimal nutrient absorption. Your body aims to replace nutrients and electrolytes lost during your workout.
After fasted cardio, your body’s net balance of protein is negative. Why? Muscle protein is partially used for energy. Since the body strives for balance, it transitions from a catabolic state, where molecules are broken down for energy, to an anabolic state, where molecules are built up for use throughout the body.
When anabolic activity is higher than catabolic activity, the body is ready to absorb nutrients. These nutrients are used to build muscle, and in order to build muscle, energy is also needed. This is why a good combination of carbohydrates, proteins, and fats are essential after a fasted cardio workout.
Again, fasted cardio should only be performed if the quality of your workout isn’t affected. Quality should always be top of mind. If you aren’t killing your workout most of the time, you may need to reconsider your strategy and might want to consider eating beforehand.
3. Improves Insulin Sensitivity
Fasted cardio has proven to increase your glycogen stores and increase your insulin sensitivity.
You’re basically giving insulin a break. With the lack of spike in blood sugar, your body becomes more sensitive to increased blood sugar levels. This means your blood sugar levels are less likely to get out of whack, and you decrease your risk of diabetes.
While the above benefits sound great, it’s likely best to run the idea of fasted cardio by your family doctor before trying it. Again, everyone is different and pre-existing conditions may come into play.
The Best Fasted Cardio Workouts
So, you’ve decided to give fasted cardio a try, but where do you start?
First off, plan a morning where you have plenty of time to workout then eat breakfast before starting your day.
Second, try any of the cardio workouts below. Get your fat burn on and that cardio workout completed!
1. Air Bikes
A HIIT workout on an air bike is one of the best forms of cardio you can do. It maximizes weight loss and can help you tone your body.
Go for a minute as hard as you can, then a minute of low-intensity. Continue to alternate between the two for 20-30 minutes to complete a full workout.
High-intensity interval training workouts aren’t just limited to the air bike. You can do HIIT workouts almost anywhere.
They’re quick and provide an excellent metabolism boost. Below I outline a 15 minute HIIT workout you can do first thing in the morning.
Set a timer for 1 minute intervals. The first minute is high-intensity – this means giving it all you’ve got. The second minute is low-intensity and is an active recovery move.
Alternate between these 2 intensities for the 5 exercises below. Do 3 rounds for a total of 15 minutes.
Plank Hold (low-intensity):
Lie facedown on a comfortable surface, with your hands under your shoulders and your legs straight back. Lift yourself up into a full plank position. Your hands should be directly under your shoulders and you should form a straight line from your head to your toes. Make sure to engage your core! Try to hold this position for 1 minute.
Boat Hold (low-intensity):
Sit on a comfortable surface, with your knees bent and your feet planted on the ground in front of you. Carefully lift your feet up off the ground and extend your arms straight in front of you. Try to hold this position for 1 minute.
High Knees (high-intensity):
Stand tall with your feet hip-width apart. Bend and drive one knee up toward your chest. As you lower your foot back down to the ground, bend and drive your opposite knee up toward your chest. Alternate legs as quickly as you can.
Squat Jumps (high-intensity):
Lower down into a squat. Push off from your heels and jump up, then return back to the start position. Repeat.
Mountain Climbers (high-intensity):
Begin in a full plank position. Drive one knee up toward your chest. As you send your knee back, drive your opposite knee up toward your chest. Continue to alternate sides as fast as you can.
If you’re looking for a longer fasted cardio program, try the 30-Minute HIIT workout below. Challenge yourself and remember to give it all you’ve got during these high-intensity intervals.
3. Fasted Sprints
Fasted sprints are another form of HIIT cardio. You give it your all during the sprints, then take a short break. Sprints are tough to keep up for a full minute, so I recommend alternating between 20 seconds on and 20 seconds off.
Another way to do it is to set a distance. Run your set distance then, walk back to the start. Like HIIT cardio, your metabolism will get a boost and you’ll burn fat in a shorter amount of time.
4. Outdoor Workouts
The great outdoors has proven to have significant impacts on mental health, including improving your mood and overall quality of life.
So, why not take your workout outside? Go for a run or a bike ride first thing or take your HIIT workout outside. Start your day off right!
You won’t only boost your body’s fat burning capabilities, but you’ll feel better overall and have improved mental clarity.
You’ll also give your body a chance to wake up naturally with some much-needed sunlight. The combination sets you up for a successful day.
What to Eat After a Fasted Cardio Workout
What you eat after a fasted cardio session depends entirely on your fitness goals. If you want to gain muscle, amp up your protein amount. Although, no matter what your goal is, you should consume enough protein to replace what was potentially lost.
For optimal fat loss, aim for a post-workout meal of 40% protein, 30% carbs, and 30% fat. In both instances, it’s important to ensure your body gets protein, carbs, and fats. However, the ratio varies based on your goals.
Why do you need all 3? Your body uses each differently, and they are all important to maintain regular and optimal functioning. Plus, you don’t want to create any sort of nutrient deficiency by attempting to reach your fitness goals.
Another aspect to note is your calorie count per day. If your goal is to lose weight, you need a calorie deficit to do so. If you want to gain muscle, you need a calorie surplus. Keep this in mind when planning your post-workout and daily meals.
Supplements for Fasted Cardio
There are also many supplements that you can take in conjunction with fasted cardio. I explore a few of these below.
Studies have proven that caffeine has fat-burning effects. As long as you don’t get heartburn from it, have your cup of joe before your workout – it could potentially increase your fat burn.
Surprisingly, caffeine increases your daily energy expenditure. This means it amps up the number of calories you burn. Caffeine can also help you push through that morning fatigue, especially when you haven’t eaten in 8 hours.
Yet, it doesn’t come without its downsides. Caffeine can cause sleeping issues, particularly in those that don’t regularly consume it, and it has been linked in excessive amounts to anxiety disorders.
Make sure to not exceed the recommended amount of caffeine pills. Always read the labels of the supplements you buy. For individuals that don’t consume caffeine on a regular basis, it may be best to take a lower dose.
- HIGHEST QUALITY: Lab-tested for potency and purity. We...
- SUPPORTS MUSCLE PROTEIN SYNTHESIS: Serves as a building...
- AIDS STRENGTH PERFORMANCE: Improves power output,...
- Help build mass^May improve recovery^Helps preserve...
Leucine is an amino acid that contributes to protein synthesis, the building of muscle. In relation to fasted cardio, leucine won’t cause insulin levels to spike. Consequently, it won’t reverse the effects of doing fasted cardio.
You can buy leucine at most health food stores. It’s also offered on Amazon. I recommend the PrimaForce L-Leucine Powder. Throw it in a smoothie or shake after your workout.
- 1G HMB PER CAPSULE – HMB can stimulate protein...
- PRESERVE & PROTECT MUSCLE – helps support muscle...
- LEAN MUSCLE MASS – aids in building lean body mass*
- STRENGTH – supports muscle strength to help you...
- SCIENTIFICALLY-TESTED – HMB is a well-studied...
HMB, or hydroxy methylbutyric acid, reduces muscle breakdown. One study even found that it “improves muscle mass and function.” Although not as effective as Leucine in building muscle, this supplement can be found in powder or capsule form.
I suggest trying the capsule form from Optimum Nutrition. A single capsule is enough to help preserve and build muscle.
- HIGHEST QUALITY: Lab-tested for potency and purity. We...
- ENHANCES MUSCLE GROWTH: Shown to increase muscle mass...
- SUPPORTS ENDURANCE: Enables you to exercise longer and...
- PROMOTES RECOVERY: Helps your muscles recover after a...
- Supports endurance^Potent arginine precursor^Supports...
Citrulline Malate is proven to improve performance and decrease post-muscle soreness. It, also, works to protect the body from cell-damaging substances.
Amazon offers a variation of Citrulline Malate from PrimaForce. It comes as a powder and is recommended to take before your workout. The only recorded side effect is stomach discomfort, which occurs in 10-15% of individuals.
Rauwolscine & Yohimbine
- Increases Fat-Burning From Exercise
- May Enhance Mood And Sexual Well-Being
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Rauwolscine is an alpha-receptor. Yohimbine is a chemical derived from the bark of the yohimbine tree. Rauwolscine and yohimbine are linked to fat-loss, particularly in elite athletes. If you’re training hard and fat loss is your goal, this supplement may prove beneficial.
Check out Rauwolscine by Singular Sport on Amazon or PrimaForce Yohimbine. Be aware that there are various side effects of using these products, such as gastrointestinal issues, anxiety, a faster heart rate, and high blood pressure. It may be best to test out the waters with lower dosages to start.
Cardio While Intermittent Fasting or Water Fasting
Intermittent fasting is where you alternate and cycle between periods of eating and fasting. For example, many people follow the 16/8 method, where 16 hours of fasting is done, with 8 hours for eating.
Why do intermittent fasting? It helps burn fat by pushing your body into ketosis. It can be a great method to control or maintain your weight and to limit your body fat percentage. If the goal is to burn fat, then doing fasted cardio before breaking your fast is ideal. This way you can replenish your protein stores in your post-workout meal.
It’s also crucial to ensure you get the proper nutrients when doing an intermittent fast. You have a shorter window to eat. This means you have to make sure you are eating nutrient-dense food, no garbage.
Water fasting, in contrast, is a set period where the only food or beverage you consume is water. Many use it as a quick way to lose weight. However, many water fasts last for longer period, such as 24-48 hours, making it vital to ensure it is done safely. Run it by your doctor before diving in.
However, exercising during a lengthy water fast may burn the wrong kind of tissue, such as muscle, leaving you weak and lacking gains. It’s often recommended to do low-intensity exercise if you must exercise at all.
Q: Is fasted cardio better than regular cardio?
A: Not necessarily. Studies show mixed results. One study indicated that body compositions didn’t change when fasted cardio groups and non-fasted cardio groups were compared. Yet, another study showed obvious fat oxidation and a decrease in energy intake 24 hours after individuals completed their fasted cardio.
Q: How long should I fast for before my fasted cardio session?
A: Many people like performing fasted cardio first thing in the morning, since this means you have 8 or more hours of fasting before your workout. However, 3-4 hours is sufficient enough to deplete insulin stores, which is the main driving force behind fasted cardio.
Q: Is it better to do cardio in the morning or at night?
A: The morning tends to prove best time and time again. Fasted cardio works best in the morning, since you haven’t eaten anything all night. Cardio in the morning also bumps up your metabolism first thing, increasing your energy and calorie burn for the rest of the day.
Q: Does running burn fat or muscle?
A: Running can burn fat or muscle. It basically depends on the length of your run. If you’re running for shorter durations, your body will only dive into the first 2 fuel sources – glucose and fat. If you run for longer periods, such as over 2 hours, your body may turn to muscle for energy.
Fasted cardio provides an array of benefits, especially if your main goal is weight loss.
Yet, it’s not for everyone. Talk with your doctor if you have any concerns or questions. Check in with yourself throughout your workout. How do you feel? Does it differ from your regular workout? If so, how?
Furthermore, remember to keep hydrated throughout your session. Fasting doesn’t mean you can’t drink water. Plus, staying hydrated prevents fatigue and promotes optimal muscle recovery.
Have you tried fasted cardio? What works for you? What doesn’t? Comment below!