Intermittent fasting involves systematic periods of zero food intake. This way of eating not only has the potential to reduce your overall calorie consumption but also helps limit the amount of glucose entering your system and trains your body to become fat-adapted.
But what happens when you workout while intermittent fasting? Is it safe to exercise and can it help to maximise your results?
Is it Safe to Exercise While Intermittent Fasting?
If you have a weight loss or fitness goal, no doubt you’re exploring ways to enhance your performance or manipulate your body composition.
The research into the benefits of intermittent fasting and exercise is growing, and not only is it proving to be safe, but it also may help you reach your health goals quickly. This is because fasting before exercise may help to reduce your energy intake and increase fat oxidation, both of which have potential benefits for weight management and changes to body composition
The Pros and Cons of Exercising in a Fasted State
There are several pros and cons to consider before you start working out in a fasted state.
Pros of exercising while fasting
- You can burn more fat as that your glycogen stores will be depleted
- It can help stabilise blood sugar levels and improve insulin sensitivity
- Exercising while fasted may boost your growth hormone and testosterone production
- It may increase your mental endurance and reduce your tension later in the day
Cons of exercising while fasting
- You may not have as much energy to fuel your workout, particularly in the beginning or if you have run out of energy stores
- You may not be able to experience significant gains in muscle mass
- You are at greater risk of electrolyte depletion and dehydration
How Should You Time Your Exercise While Intermittent Fasting?
The recommended time to schedule your workout is at the end of your fast. While it may be uncomfortable to exercise after 16 hours of fasting, however, you do get to refuel after the session.
If you’re new to intermittent fasting, it may take your body to adjust. It’s common to experience fatigue or an inability to push as hard as you’re used to.
One of the main reasons for scheduling exercise at the end of your fast is that it takes the body on average 10 to 12 hours to use up your glycogen stores and switch to burning fat. Refuelling after exercise also gives you the opportunity to provide your body with the nutrients it needs to repair and recover.
However, like all things relating to nutrition and exercise, when you time your workouts can be highly individual. Working out before the end of a fasting window will suit people who perform well on an empty stomach.
If you’re someone who doesn’t like to work out on an empty stomach and wants to focus on your post-workout nutrition, it may be better to workout out during your feeding window. This may help you increase your performance and recovery.
When you time your exercise will also be dependent on the type of intermittent fasting you have chosen. If you choose alternate day fasts or a regime such as the 5:2, you have the option to exercise on the days you are consuming a higher number of calories or on the restricted days.
The key is to listen to your body and recognise what you can push through or the signals that suggest you should stop. There’s a clear difference between being uncomfortable and being in pain. If you’re in pain, you may need to rethink your approach.
How Should You Eat After Your Workout to Break Your Fast?
One of the reasons intermittent fasting is popular for weight loss is that the limited eating window means you are eating fewer meals. While this can lead to a reduction in weight, it’s particularly important to make every meal count and opt for nutrient-dense food watching your intake of refined carbs and processed foods.
When you’re adding exercise into the mix, it’s even more vital you are refuelling adequately post-workout to support recovery, repair and muscle growth. This means opting for a whole food diet that largely features protein, complex carbohydrates and healthy fats.
Here are some refuelling ideas to break the fast after your workout:
- Smoothie with zucchini, spinach, chia seeds, nut butter and yoghurt
- Overnight oats with protein powder and berries
- Eggs with veggies
- Tuna with avocado and crackers
If you are adopting an intermittent fasting method that restricts your calorie intake during your eating window or feeding days, such as the 5:2, ensuring you have your most nutrient-dense meal after your workout may help improve your recovery.
Will Exercising in a Fasted State Help You Lose More Weight?
If weight loss is your goal, incorporating exercise into your regime may help you reach your target weight faster.
Studies have found the combination of exercising and fasting maximises the breakdown of glycogen and fat for energy. Doing a workout while in a fasted state has the potential to lower both your body weight and body fat percentage.
However, what you eat, portion control and how you exercise still matters. Generally speaking, your appetite increases after working out and it can be very easy to overeat when you break the fast. While you may have reduced your eating window, you can still eat too many calories which will make reaching your weight loss goal difficult.
If you’ve hit a weight loss plateau while fasting, you need to rethink your nutrition and the intensity and frequency of your workouts.
Can You Increase Muscle Mass While Intermittent Fasting?
It’s a myth that you will automatically lose muscle mass while intermittent fasting. If you are still fueling your body with enough protein and nutrient-dense foods throughout your day.
When you exercise in a fasted state, overtime you will increase autophagy. This facilitates muscle growth which can be further enhanced if you are doing resistance training.
If you are wanting to retain your muscle and facilitate repair, the timing of your workout and post-workout fueling is particularly important. Schedule your workout when you can follow it up with a high-protein meal that is rich in the amino acid leucine. Essential amino acids, particularly leucine help to immediately increase muscle protein synthesis and prevent muscle loss.
However, if you are wanting to achieve substantial muscle gain, fasting may not be the best solution for you as it’s very difficult to build muscle while in a calorie deficit. It is also possible that your body will start breaking down some muscle to use protein as fuel for your fasted workout.
Tips for Exercising When Fasted for Weight Loss
- Opt for a program that incorporates both resistance training and cardio to burn fat while preserving muscle mass.
- Do your cardio workout while fasted for maximum fat burning.
- Drink plenty of water throughout the day and during your workout.
- If you’re struggling with energy, ensure you’re replacing lost electrolytes.
- Choose low-intensity activities such as walking and yoga when you’re on a long fast to avoid fatigue and dehydration. Schedule your high-intensity activities during a feeding window or when you can refuel after your fasting periods.
- Plan your post-workout meals carefully to ensure you are replenishing nutrients and facilitating the repair of muscles and tissues.
Explore in more detail
- A Beginner’s Guide To Intermittent Fasting
- A Guide To The 16:8 Fast
- A Guide To The 20:4 Fast
- A Guide To The 5:2 Fast
- Intermittent Fasting And Exercise
- Intermittent Fasting And Hormone Balance
- Intermittent Fasting And Keto
- Intermittent Fasting And Type 2 Diabetes
- Intermittent Fasting And Weight Loss
- Intermittent Fasting: Tips To Starting Your First Fast
- Side Effects Of Intermittent Fasting
- Tips For Intermittent Fasting Success
- Top FAQs Of Intermittent Fasting