Should You Exercise on an Empty Stomach?

• Empty stomach exercise means that you haven't eaten for at least about 10 hours before training, which can lead to partial or complete depletion of glycogen stores.
• It is often associated with intermittent fasting, which involves alternating periods of eating and fasting (for example, in the form of 16/8).
• Skipping meals before exercise can reduce performance, motivation and enjoyment of exercise in some individuals, and it can lead to a drop in glycaemia, dehydration or increased muscle protein catabolism.

Why is empty stomach exercise popular?

Empty stomach exercise, or fasted exercise, has climbed so high on the popularity scale primarily because of circulating myths. Although most of them have been debunked thanks to long and extensive studies, a large part of the population still believes them. One common myth is that fasted exercise helps maximise fat loss. This belief is based on the idea that the body has to use stored fat as "fuel" since it has no other resources (mainly carbohydrates) available at that moment. However, individuals are more likely to experience reduced performance, motivation and enjoyment of exercise.

Fasted exercise is also often combined with the practice of intermittent fasting. Various modifications of intermittent fasting (e.g., 12/12 or 16/8) have been shown to have a positive impact on a number of health parameters. Since many people prefer to exercise in the morning, it is not surprising that these seemingly‑for‑all effective methods combine and, unfortunately, often converge negatively.

What is the truth behind these myths?

Empty stomach exercise is a debated topic mainly because of various myths and superstitions. Some of these may be based on partial truths, while others are completely unfounded. But how can we make sense of it all?

Myth: Fasted exercise will accelerate fat‑burning

Reality: Yes, if you go into a workout on an empty stomach, your body will likely be forced to use stored energy. However, the final effect can vary and depends on several factors, including the type of exercise, intensity, the individual's current fitness level, body composition, etc. Even if fats are used as the main source of energy during exercise, this effect will not be reflected in the final outcome of overall weight loss.

Myth: Fasted exercise leads to loss of muscle mass

Reality: Losing muscle mass when exercising on an empty stomach is not automatic, especially if you stay within the optimal range of your daily intake. (For more information and tips, see the article What is basal metabolic rate and how to calculate it?) With a proper diet and adherence to an appropriate training plan, empty stomach exercise can be a safe form of exercise. However, prolonged fasting and lower meal frequency throughout the day can be challenging for maintaining muscle mass as it may be difficult to consume the necessary amount of energy and nutrients in just 1‑2 servings.

Myth: Exercising on an empty stomach is ideal for everyone

Reality: The suitability of this practice, like many aspects of a healthy lifestyle, depends on individual factors, including health, fitness level, mindset and type of exercise. While some people may feel sick after even a small breakfast before less intense exercise, others won't consider working out without replenishing their energy first.

Myth: Fasted exercise increases performance

Reality: This is a myth in most cases. Without energy replenishment in the form of food, individuals often experience lower energy and performance levels. This is why it is a good idea to listen to your body and actively adapt your exercise plan according to your needs.

Myth: Fasted exercise is dangerous and harmful to health

Reality: As we outlined in the previous points, for some, exercising on an empty stomach can be a beneficial and satisfying. Just because most people prefer to eat before working out doesn't mean it's the norm. However, if you have health issues, particularly involving problems with glycemic control, you should definitely consult a professional, such as a physician or nutritional therapist, before incorporating fasted exercise.

Are there any risks?

1. Reduced performance: Most people may experience reduced performance during fasted exercise. When the body is not provided with a supply of energy — especially carbohydrates — for a long period of time, particularly before exercise, glycogen stores (the energy source stored in the muscles and liver) can be partially or completely depleted. This can cause a loss of energy and faster exhaustion, affecting endurance, strength and overall performance during exercise. It can also impact cognitive function, concentration and coordination, increasing the risk of injury.
2. Lack of motivation and enjoyment of exercise: Empty stomach exercise can cause feelings of fatigue, irritation and reduced ability to concentrate, negatively affecting the mental aspect of exercise. In addition, many may find it psychologically challenging to find the motivation to exercise. A 2021 study suggests a psychological impact on individuals, leading to potential overeating the previous evening. Participants who knew they would exercise in the morning without eating ingested more calories the previous evening.
3. Low blood sugar: This is related to the points described above. Given the absence of previous food intake, blood glucose levels may be significantly affected. Of course, a healthy body has mechanisms to maintain normal glucose levels after prolonged fasting, but in people prone to impaired glycaemic control, this can also cause hypoglycaemia. Therefore, it is important that individuals who wish to exercise on an empty stomach know their health status well and take into account individual needs to prevent potential issues.
4. Risk of dehydration: Exercising on an empty stomach may also increase the risk of dehydration due to previous prolonged fasting. This may result from a lack of fluids from meals or simply forgetting to drink during a stretch of fasting. This leads to fatigue, poor performance, and, in extreme cases, dehydration, promoting muscle weakness.
5. Fainting, dizziness, trembling: And we are back to lower blood sugar or hypoglycaemia. Individuals with impaired glucose regulation should be particularly cautious, but symptoms such as dizziness, tremors, drowsiness, and, in extreme cases, fainting can also be experienced to some extent by healthy individuals. It should be emphasised that responses to fasted exercise can vary between individuals, and proper preparation — including a balanced diet the night before and after exercise — is key to minimising the risk of these side effects.

The key to a quality and healthy workout

As mentioned several times above, personal preference is key. If you find it easier to exercise on an empty stomach, it is certainly a possible and, with some precautions, safe route to take. So, what to keep in mind and not to skip when training on an empty stomach?

1. Realistic goals: Set clear and realistic goals for your training within your means. Planning will help you stay motivated and monitor your progress.
2. Exercise variety: Incorporate as much natural movement that you enjoy into your plan as possible. This will help develop different aspects of fitness and reduce the risk of overloading or tiring of one type of exercise.
3. Proper technique: Pay attention to proper exercise techniques to minimise the risk of injury. If you are unsure of your abilities, consult a professional trainer to help you learn how to perform the exercises correctly. 
4. Gradual increase in intensity: This point is related to realistic goals. Increasing the weight or volume of an exercise too quickly can increase the risk of overload and injury.
5. Adequate rest: Make sure you get enough rest between workouts or training days. This is essential for muscle recovery and preventing overtraining.
6. A balanced diet: Eat a varied and balanced diet. Each of your meals should contain all macronutrients and enough vitamins and minerals for optimal performance and recovery. 
7. Hydration: Insufficient fluid intake can not only negatively affect performance and slow recovery but also impair cognitive function.
8. Include stretching: Don't skip stretching before or after your workout to ensure flexibility and mobility. This will help prevent injury and strain and improve your training routine.
9. Listen to your body: Pay attention to your body's signals. If you're exhausted or even a little sore, reduce the intensity of your workouts or give yourself more time to recover.
10. Quality sleep: Sleep is the foundation of everything. For many reasons, sleep is crucial for regenerating the body, restoring energy reserves and optimal mood, and much more.

Bottom line

Although empty stomach exercise may seem like a more effective form of workout without enough research, the truth is usually elsewhere. Myths about maximum fat loss or increased performance have been proven to be largely incorrect. On the contrary, the risks associated with this practice include decreased performance, lack of motivation or energy to exercise, greater dehydration, and more. However, some people are comfortable with this form of exercise, in which case be sure to consider your individual needs and goals. The purpose of this article is to remind you that achieving your goals is not so much about whether you exercise with a full or empty stomach but rather about the overall setup of your training plan and diet.