Today, we’re going to dive into a topic that generates quite a bit of debate in the fitness and health world: fasted cardio training. Basically, this is performing cardio exercises (such as running, swimming, and cycling) after an overnight fast, typically without having eaten beforehand.
The recurring question is: Should you do it? Well, as with many wellness-related matters, the answer isn’t a simple “yes” or “no”. Whether fasting while working out is beneficial for you will depend on several factors.
In this blog post, we’ll break down the potential benefits and important considerations. We’ll also guide you on what to eat after your fasted workout to maximize recovery and optimize your results. That way, you could make an informed decision that’s tailored to your specific needs and goals.
Before we dive into the potential benefits, it’s crucial to understand what exactly “fasted cardio” means. As previously mentioned, it refers to the practice of performing cardio exercises, such as running, swimming, cycling, or brisk walking, after an extended period without consuming food. Typically, this fasting period lasts at least 8 hours, and the exercise is often done in the morning before eating breakfast.
During this time, glycogen levels (the stored form of glucose) in the liver and muscles are relatively low, which, in theory, forces the body to turn to other energy sources – primarily using stored fat as fuel during the workout (1). Therefore, one of the most notable and sought-after claimed benefits of fasted cardio is weight loss (2).
However, it’s important to understand that this increased fat oxidation during exercise does not necessarily guarantee greater long-term weight loss. Weight loss is a complex process that depends on many factors, including overall caloric balance (consuming fewer calories than you burn), your diet composition, and the type and intensity of the exercise you perform (3).
Our previous post goes into great detail about the fasting workout.
Beyond the potential contribution to weight loss from greater fat oxidation, fasted cardio is claimed to positively influence:
That being said, it’s essential to recognize that results from fasted cardio vary significantly between individuals, and factors such as exercise intensity, duration of the fast, and overall diet play fundamental roles.
Speaking of individuality, we would like to pay special attention to differences between men and women. Female physiology is more complex, and hormonal fluctuations across the menstrual cycle could influence the body’s response to fasted exercise and, in general, the benefits of fasted cardio for women. It’s possible that women might need to adjust their approach and listen more closely to their body’s signals at certain times of the month (9). We would suggest discussing these and any individualized considerations or concerns with your healthcare provider.
Read more: Fasting Phases: What Your Body’s Really Doing When You Skip a Meal
The question of the ideal duration for fasted cardio is common, and while running on an empty stomach might sound appealing to speed up weight loss, there isn’t a one-size-fits-all answer. The optimal duration depends on several factors, including your fitness level, experience with fasted training, the intensity of the workout, and your individual goals.
Generally, 20-30 minutes of fasted cardio at low to moderate intensity (such as a brisk walk or a light jog) could be a good starting point for most people. This range could allow you to explore how your body responds to this training style without significantly compromising your energy levels (10).
Monitor how you feel: do you experience dizziness, weakness, or a dramatic drop in performance? If so, reduce the duration or intensity. As your body adapts, you could gradually increase the length of your sessions, but always listen to your body! And remember that hydration is essential, so be sure to drink water before, during, and after your workout.
Finally, you should keep in mind that overall nutrition and a healthy lifestyle are far more important than the specific time of day you do cardio. Ideally, consult a health professional to get personalized guidance and a plan tailored to your needs and goals.
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As with duration, there isn’t a single, universal answer. The optimal frequency to reap the benefits of fasted cardio in the morning depends on several individual factors, including your fitness level and personal goals.
Generally, doing fasted cardio 2-3 days per week could be a good starting point for most people. It’s essential to start gradually, monitor how your body responds, and adjust the frequency and intensity as needed.
If, after a few weeks, you feel comfortable and are experiencing the desired benefits, you could consider increasing the frequency to 4 or even 5 days per week. And as always, we remember the importance of giving your body enough rest and nutrition to recover properly.
As we’ve mentioned throughout this article, post-fasted cardio nutrition is important to ensure proper nutrient replenishment.
However, as the replenishment of nutrients will depend a lot on the intensity and duration of your fasted cardio, we’ll consider two key scenarios: low-intensity and/or short-duration cardio, and high-intensity and/or long-duration cardio.
We understand low-intensity cardio as brisk walking, a gentle elliptical session, or a relaxing yoga class. Generally, these activities last between 20 and 45 minutes and don’t significantly raise heart rate or dramatically deplete glycogen stores.
In this case, the urgency to replenish carbohydrates is lower. This doesn’t mean you should ignore post-exercise nutrition, but you could be more flexible and prioritize a balanced meal that includes:
Examples of post-cardio meals for low intensity include:
This scenario includes activities such as running at a fast pace, HIIT, intense cycling, or swimming at a vigorous pace, lasting more than 45 minutes (often over an hour). In this case, glycogen replenishment is crucial for optimal recovery.
Therefore, the priority here is to restore those stores and provide the nutrients needed to support your muscles after exercise:
Examples of post-cardio meals for high-intensity include:
Read more: Working Out While Fasting: How To, Benefits, And Tips
Although many people feel good and feel that they gain benefits from fasted cardio, there are a few things you should keep in mind. There isn’t a single rule that fits everyone. Whether fasted cardio works for you will depend on personal factors such as your activity level, how long you’ve been training, and how your body responds to fasting.
As previously mentioned, fasted cardio could put more demand on your body, especially if it’s high intensity. That’s why it’s worth assessing your training and how you feel during exercise before adding it to your routine. If you’re new to fitness, or you’re recovering from a period of inactivity, it may be more beneficial to start with low-intensity cardio after consuming a light meal, and then gradually progress to low-intensity fasted cardio.
Similarly, it’s important to listen to your body. If you experience dizziness, fatigue or any discomfort during fasted cardio, this suggests that it might not be the best option for you right now. Pay attention to how your energy, mood, and performance change throughout the day.
In summary, the key is moderation and self-observation. Experiment mindfully and adjust your routine according to your needs. And most importantly, if you have any questions or concerns about whether fasted cardio is right for you, we recommend consulting a qualified health professional.
Remember that health comes first, and it’s essential to make informed and safe decisions regarding your well-being.
It depends! Enough for what? If you’re just starting, it could be an excellent beginning to see how you feel and how well you tolerate it. If your goal is fat loss and you already have experience, 30 minutes could be fine if you’re doing high-intensity exercise. Listen to your body! It could be good to exercise on an empty stomach for some people. The answer varies – some people find that they feel lighter and burn fat more efficiently, while others experience fatigue and lower performance. Listen to your body and experiment to see what works best for you. You’ll get a ton of benefits from exercise, whether you’re fasted or not. No! In fact, it’s highly recommended. Water is essential for optimal performance and general health. Make sure you’re hydrated before, during, and after your workouts. Lower to moderate-intensity cardio tends to burn more fat in the moment. However, it’s important to remember that in terms of weight loss, fat burning mostly depends on your overall energy balance. This means reducing calorie intake and increasing physical activity, ideally both cardio and strength training. Generally, it also depends on consistency. The important thing is to find something you enjoy and can maintain in the long term. Aiming to maximize fat burning while preserving muscle during cutting phases is a common practice among bodybuilders. However, it’s important to emphasize that it’s not for everyone and should be done with caution and under the supervision of a professional. Fasted cardio could raise cortisol as a natural bodily response, particularly if it’s incredibly intense and prolonged. However, the increase is usually temporary and not necessarily harmful if it’s managed properly with adequate nutrition and rest.Frequently Asked Questions
Is 30 minutes of fasted cardio enough?
Is it good to work out on an empty stomach?
Does drinking water break fasted cardio?
Which cardio burns the most fat?
Why do bodybuilders do fasted cardio?
Can fasted cardio raise cortisol?
Fasted cardio is a nuanced topic. While some people report benefits such as a greater perceived fat burn during the session, these effects can vary from person to person. There isn’t a one-size-fits-all rule – the decision to do fasted cardio should be based on your training history, your goals, and your personal response to fasting.
Start gradually, listen to your body, and adjust the frequency, duration, and intensity according to how you feel. If you have any doubts, it’s best to consult a healthcare professional and tailor the plan to your needs.
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