The practice of running on an empty stomach, often referred to as “fasted running” or “morning exercise”, has been a subject of debate within the fitness and sports nutrition communities. For some, running fasted offers potential benefits like improved fat burn and weight loss, while others warn about the risks of fatigue, hypoglycemia, and potential negative impacts on performance and body composition.
As an endurance athlete or fitness enthusiast, understanding the pros and cons of running on an empty stomach can help you make informed decisions about your training regimen and fueling strategies. This article delves into the potential advantages and drawbacks of fasted running, exploring factors such as aerobic exercise, cortisol levels, personal trainer recommendations, and the role of pre-workout meals.
Potential Benefits of Running on an Empty Stomach
One potential benefit of running on an empty stomach is increased fat burn. Some studies suggest that fasted running may increase fat oxidation and fat burn compared to running after eating [1] [11]. This is because when carbohydrates are not readily available, the body is forced to rely more on stored fat for fuel [3] [7].
Another potential advantage is reduced energy intake. A few small studies found that fasted exercise can lead to lower energy intake over 24 hours [1] [11]. This could potentially aid in weight loss, though proper post-run fueling is crucial [4].
Fasted running may also offer the following benefits:
- Improved aerobic endurance: One small study found fasted exercise was associated with higher VO2 max, a measure of aerobic fitness [1] [11].
- Less digestive issues: Running on an empty stomach may reduce exercise-induced digestive problems like cramps, nausea, and diarrhea [1] [11] [6]. It can prevent stomach discomfort by avoiding food or liquid sloshing around during the run [2].
- Encouraging fat utilization: Fasted running may prompt the body to use fat reserves for energy rather than just glycogen, potentially enhancing endurance [4].
- Beneficial physiological changes: Fasted running may improve insulin regulation and lower cholesterol levels, improving health and performance [4].
- Mental benefits: Some runners report feeling a sense of accomplishment and fresh ideas early in the day after a fasted run [5].
It’s important to note that while fasted running may offer potential benefits, it should be balanced with regular carb-fueled workouts, especially for beginners [8]. Additionally, the evidence suggests that those who run fueled may outperform those who run fasted [9].
Drawbacks and Risks of Running on an Empty Stomach
While fasted running may offer some potential benefits, it’s crucial to be aware of the potential drawbacks and risks associated with this practice:
- Risk of Hypoglycemia (Low Blood Sugar): Running on an empty stomach can lead to dangerously low blood sugar levels, especially for individuals with diabetes or Addison’s disease [1] [2] [10]. This can result in dizziness, fatigue, and impaired cognitive function, increasing the risk of injury [3].
- Decreased Performance and Intensity: Fasted running may negatively impact exercise performance and intensity due to a lack of readily available energy sources [3] [10]. You may experience earlier fatigue, reduced endurance, and an inability to maintain high intensity or pace [1] [2].
- Muscle Loss and Hormonal Imbalances: Fasted exercise in the morning can elevate cortisol levels, potentially leading to muscle breakdown and loss [1] [10]. Additionally, it may disrupt hormonal balance, particularly in women, and reduce testosterone levels in men [7].
- Gastrointestinal Distress: If you consume a heavy or high-fat/protein/fiber meal before running, digestion can slow and impact your exercise [3]. Eating too close to exercise can also cause gastrointestinal discomfort [3].
- Increased Appetite and Overeating: Fasted running may lead to increased appetite and overeating later in the day to compensate for the depleted energy stores [2] [10]. This could potentially offset any potential weight loss benefits.
- Ineffective for Long-Term Weight Loss: While fasted running may increase fat burn during exercise, the body may compensate by reducing fat burn later in the day [1] [10]. Additionally, it may not necessarily promote more overall fat-burning or weight loss compared to running after eating [2].
It’s important to note that for most runners, especially those focused on performance, the potential drawbacks of fasted running may outweigh the benefits [6] [9]. Individual factors, such as fitness level, goals, and personal preferences, should be considered when deciding whether to incorporate fasted running into your training regimen.
Fueling Strategies for Running
The body’s muscles rely on two primary fuel sources: carbohydrates and fat [11]. Carbohydrates are broken down into glucose, which is the body’s preferred fuel during exercise [11]. When glucose is depleted, the body taps into stored glucose (glycogen) in the liver and muscles [11]. Once glycogen stores are exhausted, fat is then utilized as a backup energy source [11].
For intense or long runs, it’s crucial to consume a light, carb-rich snack 1-3 hours before running to provide energy [1]. Here are some fueling strategies to consider:
- Carbohydrate Loading: Long-distance runners should aim to obtain most of their calories from complex carbohydrates like pasta, oatmeal, and potatoes for sustained energy [11]. Before a long run, focus on simple carbohydrates that can be readily utilized, such as fruit, sports drinks, and energy gels [11]. Avoid high-fat meals before a run, as fats are not quickly converted to energy [11].
- During Exercise: For runs or races lasting longer than 90 minutes, aim to consume 30-60 grams of carbohydrates per hour through beverages or food [11]. Two cups of a regular sports drink contain approximately 30 grams of carbohydrates [11].
- Protein for Recovery: Protein is essential for muscle repair after a run [11]. Consume adequate protein throughout the day and within 30 minutes after a workout for optimal recovery [11]. Good protein sources include meat, chicken, fish, eggs, dairy, tofu, and beans [11].
- Personalized Nutrition Plan: Specific calorie, carbohydrate, protein, and fat needs vary by individual based on age, gender, activity level, and medical conditions [11]. Seeking guidance from a registered dietitian can help optimize your fueling strategy [11].
| Pre-Run Fueling | During Exercise | Post-Run Recovery |
| 200-300 calories, 3:1 ratio of carbs to protein [12] | 30-60g carbs/hour for runs >90 mins [11] | Protein within 30 mins for muscle repair [11] |
| Eat 1-2 hours before to allow digestion [12] | Sports drinks, gels, trail mix [11] [13] | Protein shake if meal delayed [13] |
| Bananas, rice, toast, cereal, energy bars [12] | Liquid/glucose refueling after 5-10km [13] | 1.2-2.0g protein/kg body weight [13] |
It’s recommended to add 100 calories to your daily intake for every mile run, with 65% of daily calories coming from carbohydrates [13]. Most runners find it better to fuel up with carbs the night before rather than a big breakfast, which can cause digestion issues [13]. For optimal running performance, fueling before and after runs is recommended, especially for those prone to injury, fatigue, or poor recovery [9]. Proper hydration and refueling with carbs and protein after a fasted run is important to aid muscle recovery and replenish glycogen stores [8].
Factors to Consider
There are several important factors to consider when deciding whether to incorporate fasted running into your training routine:
- Pace and Intensity: Maintain a relaxed, aerobic pace with a heart rate around 120 beats per minute during fasted runs to avoid overstressing your body [5]. Avoid high-intensity interval training or tempo runs, as your body may feel stiff and immobile in the morning [5].
- Timing: Perform fasted runs first thing in the morning, immediately after waking up and without eating breakfast [5]. Your last meal should have been consumed 6-8 hours prior to the fasted run [5]. If it’s still dark outside, wear a headlamp for safety [5].
- Duration: If you’re new to fasted running, start with a short 20-minute run and gradually increase to 40-60 minutes as your body adapts [5]. Experienced runners can attempt longer fasted runs up to 2 hours, but it’s advisable to carry an emergency carbohydrate ration just in case [5].
- Convenience: Run directly from your front door to avoid unnecessary time spent getting to a starting point [5]. Fasted runs can be done anywhere, even on vacation, to explore new areas early in the morning [5].
- Conditions: Don’t let weather conditions deter you from fasted running, as the fresh air and sense of accomplishment can be rewarding [5].
- Balance: Fasted runs should not be the only type of running you do, but rather one training tool used in combination with other workouts [5] [6]. Start with short, easy runs when trying fasted running before attempting longer or more intense workouts [6].
| Key Considerations | Guidelines |
| Pace and Intensity | Maintain a relaxed, aerobic pace (around 120 bpm) [5] . Avoid high-intensity workouts [5] . |
| Timing | First thing in the morning, 6-8 hours after the last meal [5] . |
| Duration | Start with 20 minutes, gradually increase to 40-60 minutes [5] . Experienced runners can go up to 2 hours with emergency fuel [5] . |
| Convenience | Run directly from your front door [5] . Explore new areas while traveling [5] . |
| Conditions | Run in any weather conditions for a sense of accomplishment [5] . |
| Balance | Use fasted running as one training tool, not the only type of workout [5] [6] . |
Additionally, it’s important to note that fasted running should only be done in heart rate Zones 1 and 2, not before high-intensity runs, and should only be done 1-2 times per week [7]. Fasted running may benefit those with prediabetes or metabolic syndrome, but is not recommended for most premenopausal women, underweight individuals, youth athletes, those recovering from injury, or those under high chronic stress [7]. If you are prone to fatigue, injury, or recovery issues, making fueling before every run a priority is recommended [9].
When to Avoid Running on an Empty Stomach
While fasted running can offer potential benefits for some individuals, there are certain situations where it’s advisable to avoid running on an empty stomach:
- Intense or High-Intensity Training: If you’re planning a high-intensity interval training (HIIT) session, a tempo run, or any other strenuous workout, it’s best to fuel up beforehand. Running on an empty stomach may not provide enough energy for these demanding exercises, leading to fatigue, poor performance, and an increased risk of injury [1].
- Training for a Major Race: If you’re training for a marathon, half-marathon, or any other major endurance event, fasted running is generally not recommended. The high energy demands of such training may be too much for the body to handle without proper fueling [8].
- Chronic Conditions or New to Exercise: If you have a chronic medical condition, such as diabetes, or if you’re new to exercise, it’s essential to consult with a healthcare professional before attempting fasted running. Running on an empty stomach may exacerbate certain conditions or pose risks for those unaccustomed to physical activity [1].
- Feeling Lightheaded or Unwell: If you feel lightheaded, dizzy, or unwell during a fasted run, it’s crucial to stop immediately and refuel. Continuing to exercise in this state can be dangerous and may lead to hypoglycemia (low blood sugar) or other complications [1].
| Situation | Recommendation |
| Intense or High-Intensity Training | Fuel up before the workout to ensure adequate energy levels [1] . |
| Training for a Major Race | Prioritize proper fueling to meet the high energy demands [8] . |
| Chronic Conditions or New to Exercise | Consult a healthcare professional before attempting fasted runs [1] . |
| Feeling Lightheaded or Unwell During a Run | Stop immediately and refuel to avoid potential complications [1] . |
It’s important to listen to your body and adjust your fueling strategies accordingly. While fasted running can be a useful tool for some individuals, it’s not a one-size-fits-all approach. Prioritizing your health and safety should always come first.
Hydration and Recovery
Proper hydration is crucial for runners, especially when engaging in fasted running. Here are some key guidelines to follow:
- Drink 17-20 fl. oz. (500-600 ml) of water about 2 hours before a sustained, fast-paced run [14]. This will ensure you’re well-hydrated before starting your workout.
- During the run, drink 5-10 fl. oz. (150-300 ml) of water every 15-20 minutes [14]. Staying hydrated will help maintain your performance and prevent fatigue.
- After the run, drink 16-24 fl. oz. (475-710 ml) of water for every pound (0.45 kg) lost during the run [14]. This will help replenish the fluids lost through sweating.
Water is the best option for hydration before, during, and after running [14]. However, sports drinks can also be beneficial in certain situations:
| Hydration Needs | Recommended Drink |
| Before/During Runs | Sports drinks with low carb concentration (<8%) [14] [16] |
| After Runs | Sports drinks with higher carb concentration (>8%) [16] |
| Electrolyte Replenishment | Sports drinks, gels, or salt tablets [15] [16] |
When running for more than an hour, aim to drink 50-250 ml (1.7-8.5 fl. oz.) of fluid every 20 minutes, up to a maximum of 750-1,000 ml (25-34 fl. oz.) per hour [15]. This will help maintain your hydration levels and prevent overhydration (hyponatremia).
Recovery drinks with protein may also help your muscles rebound more quickly after a fasted run [14]. Additionally, plan your route to include water fountains or your car as a refill station, and set a timer to remind yourself to drink regularly during the run [14]. Early signs of dehydration include dry mouth and decreased energy or performance [14].
Remember, staying hydrated is essential for optimal performance and recovery, especially when running on an empty stomach. By following these guidelines, you can ensure that you’re properly fueled and hydrated throughout your fasted runs.
Practical Tips for Fasted Running
The easiest way to start fasted running is to go for a run first thing in the morning after waking up and before eating anything [6]. This allows you to take advantage of the overnight fast and maximize the potential benefits of fasted exercise.
When first trying fasted running, it’s recommended to start with a short, easy workout rather than a long run or speed workout, and gradually increase the duration and intensity as your body adapts [6]. Here are some practical tips to help you ease into fasted running:
- Start Small: Begin with short runs of 20-30 minutes at an easy, conversational pace [6] [8]. This will help your body adjust to the new routine without overwhelming it.
- Listen to Your Body: Pay attention to how you feel during and after your fasted runs [8]. If you experience dizziness, lightheadedness, or excessive fatigue, it may be a sign that you need to refuel or adjust your approach.
- Hydrate Well: Proper hydration is crucial when running on an empty stomach [14]. Drink water before, during, and after your run to prevent dehydration and maintain optimal performance.
- Timing and Frequency: Fasted running should only be done in heart rate Zones 1 and 2 (easy to moderate intensity) [7], and should be limited to 1-2 times per week [7]. This will allow your body to recover and adapt to the new stress.
- Off-Season Experimentation: The best time to experiment with fasted running is during the off-season or base-building phase [8]. Start with easy runs and gradually increase the intensity as your body adapts.
| Tip | Guideline |
| Start Small | Begin with short runs of 20-30 minutes at an easy pace [6] [8] . |
| Listen to Your Body | Pay attention to how you feel and adjust accordingly [8] . |
| Hydrate Well | Drink water before, during, and after your run to prevent dehydration [14] . |
| Timing and Frequency | Limit fasted runs to heart rate Zones 1 and 2, 1-2 times per week [7] . |
| Off-Season Experimentation | Experiment during the off-season or base-building phase, starting with easy runs [8] . |
Remember, fasted running is not suitable for everyone, and it’s essential to listen to your body and adjust your approach accordingly [6] [7] [8]. If you experience any adverse effects or have concerns, it’s best to consult with a healthcare professional or a qualified coach.
Individual Experimentation
Fasted running, or running on an empty stomach, typically refers to running first thing in the morning before consuming any food or after an overnight fast of 10 or more hours [7] [9] [6]. While it may work for some runners who don’t experience significant performance declines or digestive issues [6], it’s essential to approach fasted running with an individualized and experimental mindset.
To support your body’s recovery and repair after a fasted run, prioritize consuming high-protein snacks like edamame, eggs, nuts, and hummus [17]. These protein-rich foods will help rebuild and maintain muscle mass. Additionally, pair these proteins with complex carbohydrates to replenish your body’s glycogen stores [17].
| Post-Run Recovery | Purpose |
| High-protein snacks (edamame, eggs, nuts, hummus) | Support muscle recovery and repair [17] |
| Complex carbs (whole grains, fruits, vegetables) | Replenish glycogen stores [17] |
| Stretching (60-90 minutes) | Improve flexibility and range of motion [17] |
| Foam rolling | Loosen myofascial tissues and reduce soreness [17] |
| Quality sleep (7-9 hours) | Allow the body to repair and recover [17] |
| Ice bath (15 minutes) | Reduce inflammation and soreness [17] |
| Cross-training (yoga, swimming) | Give running muscles a break [17] |
To further aid recovery, spend 60-90 minutes on stretching, using tools like ropes to target key areas like your hips and hamstrings [17]. Incorporating foam rolling can also help loosen up myofascial tissues and improve flexibility [17]. Prioritizing 7-9 hours of quality sleep per night is crucial, as it allows your body to repair and recover from the stress of fasted running [17].
Additionally, trying an ice bath for 15 minutes can help reduce inflammation and soreness [17], while cross-training with low-impact activities like yoga or swimming can give your running muscles a much-needed break [17].
Conclusion
The practice of running on an empty stomach, or fasted running, has sparked debate within the fitness community. While it may offer potential benefits such as increased fat burn and improved aerobic endurance for some individuals, it also carries risks like decreased performance, muscle loss, and an increased risk of hypoglycemia. Ultimately, the decision to incorporate fasted running into your routine should be based on individual factors, goals, and consultations with healthcare professionals or qualified coaches.
At the end of the day, finding the right fueling strategy that optimizes your performance and aligns with your lifestyle is crucial. Whether you choose to experiment with fasted running or prefer to fuel up before your workouts, prioritizing proper hydration, balanced nutrition, and adequate recovery remains essential for any runner. By listening to your body and adjusting your approach accordingly, you can create a sustainable and effective training regimen that supports your overall health and fitness goals.
FAQs
Is Running on an Empty Stomach Recommended?
Running on an empty stomach can lead to increased fat burning since the body uses stored fat for energy due to lower glycogen levels. Over time, this can result in fat loss. Additionally, fasted workouts can enhance insulin sensitivity, aiding in better blood sugar management.
How Does Running Without Eating First Affect Your Body?
Running without eating first may contribute to health benefits such as increased fat burning during exercise and potentially reduced calorie intake throughout the day. Regular practice might also improve the body’s response to blood sugar spikes post-eating.
What Are the Benefits and Drawbacks of Running Regularly?
Running offers several advantages, including high calorie burn, which supports weight loss, and the potential to experience a runner’s high. However, it does place significant stress on the joints, presenting a notable drawback.
What is the Maximum Time You Can Run on an Empty Stomach?
The duration one can run on an empty stomach varies by individual but generally, short and easy runs under an hour are manageable. Over time, it’s possible to gradually increase the duration without significant issues, although the intensity of these runs is likely to stay low.
References
[1] – https://www.healthline.com/health/exercise-fitness/running-on-an-empty-stomach
[2] – https://www.verywellfit.com/is-it-ok-to-run-on-an-empty-stomach-2911553
[3] – https://www.quora.com/Is-it-better-to-run-on-an-empty-stomach-or-after-eating-for-cardiovascular-fitness
[4] – https://therunningchannel.com/should-you-run-fasted-to-run-faster/
[5] – https://blog.runningcoach.me/en/2022/08/01/fasted-running-what-is-important-to-consider/
[6] – https://marathonhandbook.com/fasted-running/
[7] – https://alpinefuelnutrition.com/the-pros-and-cons-of-running-fasted/
[8] – https://medium.com/runners-life/fasted-running-should-you-do-it-and-how-4d8af64fcc5a
[9] – https://www.tcmevents.org/post/can-running-fasted-improve-performance
[10] – https://www.220triathlon.com/training/run-training/the-benefits-and-risks-of-fasted-running-on-performance
[11] – https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/fueling-your-run-with-good-nutrition
[12] – https://www.runnersworld.com/uk/nutrition/a774073/how-to-fuel-your-long-runs/
[13] – https://formnutrition.com/us/inform/nutrition-for-runners-how-to-fuel-yourself-before-during-and-after-a-run/
[14] – https://www.rei.com/learn/expert-advice/trail-running-hydration-basics.html
[15] – https://www.runnersworld.com/uk/nutrition/a761780/rws-complete-guide-to-hydration/
[16] – https://www.runnersneed.com/expert-advice/nutrition-and-hydration/how-to-stay-hydrated.html
[17] – https://www.redbull.com/us-en/running-recovery-tips