Intermittent Fasting and Running: A Winning Combination or a Terrible Mistake? 

Run, fasting, run. 

This scheme could be your winning strategy for new running sessions. The thing is, intermittent fasting boasts many benefits but assures some drawbacks as well. Especially during running sprees, you should be wary of your calorie intake as your body needs enough fuel to run. 

I guess you’re either a running enthusiast who wants to incorporate intermittent fasting or someone who is sincerely curious to know whether or not HIIT and IF can work together at all. 

I should caution you before you jump directly into this discussion: there is no clear answer to this question. Yes, it’s frustrating, I know. Truth be told, you will have to rely on yourself and try out various options to uncover the most effective way on your own.

I have no idea what kind of goals you’re pursuing: weight loss, enhanced endurance, and/or better body composition, or you simply yearn to find out how hard you can challenge yourself.

The rule of thumb here is simple: go slowly and smoothly. No need to exhaust yourself. Intermittent fasting and running: a winning combination or a terrible mistake? To be fair, it’s up to you to decide, as no one knows your body as well as you do. 

This discussion should help you get closer to the truth and get a clearer answer which will contribute to your making the right personal choice. 

Can I run while intermittent fasting?

In general, yes, you can run while fasting. Intermittent fasting and running for beginners and more advanced joggers still may be tough. Since running is energy-demanding, you should consider a few things: 

1. Your workout schedule and their intensity;
2. The type of fasting;
3. Your body needs;
4. Post-run recovery.

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Your workout schedule and their intensity

Here’s the lowdown, intermittent fasting and running is an exasperating combination leading to benefits and drawbacks as well. You shouldn’t go for long, sweating runs during the fasting period. 

It’s no rocket science that intermittent fasting can provoke fatigue and low energy (14). No wonder that intermittent fasting might lead to low blood sugar which causes you to feel tired and weak. 

Plus, intermittent fasting may be responsible for sleep disturbances in some people, which can make you tired and moody for the rest of the day. Hence, pumping it all up with high-intensity training is not the best option for you. Check out the Intermittent Fasting Exercise instead. 

There are two things you could do to combine intermittent fasting and healthy running: start running shorter distances and at lower speeds. You won’t get exhausted that quickly. In addition to this, make sure you’ve obtained enough calorie fuel before your run. 

Eating before running is a good way to prepare your body for effective physical performance. Plus, studies highlight the positive outcomes of exercising after you consume food. The major benefit is prolonged aerobic performance (5). You can plan your runs to be during your eating windows to allow you to fuel up first. 

The type of fasting

There are seven common ways to intermittent fasting: 

• Fast for 12 hours a day. The rule here is to abstain from food for 12 hours each day.
• Fasting for 16 hours. Also called, a 16:8 fast leaving an eating window of 8 hours.
• Fasting for 2 days a week. A 5:2 diet where you eat a normal amount of food on 5 days of the week and reduce your calorie intake to 500-600 calories on 2 non-consecutive days.
• Alternate-day fasting. Fast every other day. On fasting days some people reduce their calorie intake to 500 while others abstain from solid food altogether.
• A 24-hour weekly fast. A more extreme form of intermittent fasting involves not eating food for 24 hours straight. People on this diet plan drink water, tea, and other calorie-free drinks during the fasting period.
• The Warrior Diet. One of the most challenging forms of intermittent fasting. On the Warrior Diet, you eat very little, usually just a few servings of raw fruit and vegetables, during a 20-hour fasting window, then consume one large meal at night. The eating window is usually only around 4 hours (15).
• The 36-Hour Fast is another difficult type that you should try only after you’ve practiced the previous fasting types and discussed it with your healthcare provider.

For sure, engaging in short or long runs during the last three types of fasting would likely be difficult if not unsafe. 

It will be beneficial for you to run after you’ve had your meal during the eating period. This will help you avoid the potential risks of intermittent fasting combined with running. 

Your body needs

Always listen to your body’s needs. Intermittent fasting brings out various risks, starting from headaches (9) to possible dehydration (during the first fasting days, the body releases large amounts of water and salt in the urine. This process is also called diuresis (8). Without replacing the fluids and electrolytes, you can become dehydrated.

That’s why you should always stay hydrated when you begin running during fasting periods. Also, if you’re feeling weak, dizzy, or fatigued, stop running and do a recovery pause. 

Even with milder types of fasting, it can be challenging to enjoy your running routine during fasting. 

Post-run recovery

After your running race, always recover healthily. It includes: 

• Rehydration. Ideally, drink around 16-20 ounces of fluid for every pound you lose.
• Try keeping your feet elevated for 15–25 minutes.
• Consume a recovery meal containing protein, preferably in liquid form. Don’t drink processed fruit juices or other sugary substitutes (13).
• Of course, don’t forget about the cooling down mode in the form of stretching.

It’s important to refuel your body with enough nutrients before you start fasting again.. 

Read more: Beach Running Workout 101: A Comprehensive Guide to Sand Training

Do athletes do intermittent fasting?

Yes, there are athletes who eagerly start their intermittent fasting journey. Some studies demonstrate the potential motivation and benefits of intermittent regimes. A 2017 scholarly article from the academic publication called The Journal of the International Society of Sports Nutrition focuses on diets and body composition in athletes.

The researchers explored the research on intermittent fasting and other diets and body composition. They concluded that intermittent calorie restriction does not confer any advantage over continuous calorie restriction for improving body composition (12).

This is not the end though. There is another research in the journal Sports that has highlighted the fat-burning and weight-loss qualities of intermittent fasting in non-athlete populations, which have yet to be demonstrated in athletes  (10).

The researchers advise that athletes who want to lose weight using an intermittent fasting diet should be careful about when and how they exercise, train, and compete (10).

What happens when you jog while fasting?

Your body is changing when you jog or run while fasting, there’s no doubt. There are versatile Stages Of Intermittent Fasting generally impacting your result. 

Just look into a couple of studies addressing the benefits of intermittent fasting for runners: 

1. A meta-analysis in 2020 suggests that although study outcomes are conflicting, intermittent fasting may decrease fat mass and body mass (6). If weight loss is your reason for running, then intermittent fasting may help as well.
3. A small study in the Journal of Applied Physiology discovered that people (men) who consistently trained in a fasting state for six weeks demonstrated metabolic adaptations compared to those who ate before working out (1).
4. Another small study found that exercising after fasting overnight resulted in performance improvements in cyclists (4).

Overall, whether it’s jogging or long-distance running while fasting, you can reap the potential benefits. You should never forget that those benefits may not be your case. We are different and our bodies react differently. 

Your job here as a jogger or runner is to experiment with different options. Pick up the easiest fasting type and implement it into your jogging regime. Observe how you’re feeling for the first two to three weeks. 

Don’t ignore backfires: dizziness, fatigue, or exhaustion. You don’t want to hurt yourself. On top of that, intermittent fasting and running benefits are going to be more visible if you use professional help. 

Contact your healthcare provider and discuss the important steps to make your running-fasting routine more productive and less harmful. 

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What are the negative side effects of intermittent fasting?

Despite all the wonderful things I wrote about the possible benefits of intermittent fasting for runners, there are potential pitfalls for them too. 

Nothing is perfect. We, human beings should know it as we aren’t perfect on our own.  

Here I’m presenting you the possible negative side effects of intermittent fasting:

1. Some intermittent fasting plans are not good for athletes, as they are mostly low-carb. An article in the academic journal Nutrition suggests the importance of carbohydrate consumption for athletes who train for competition. 

In many intermittent fasting plans, dieters eliminate carb-rich foods to lower their calorie consumption on fast days. In reality, carbs are crucial in an athlete’s diet. They break down as energy to burn during training and competitive performances. The study states that athletes shouldn’t adopt a carb-restricted diet because they need enough energy to perform (3). Nonetheless, the study also highlights that more research is needed at this point. 

2. Intermittent fasting and marathon training are probably not a good idea to do together. One 2020 review in the Journal of Sports Medicine on fasting’s impact on performance advises endurance athletes to avoid high-intensity training while in a fasted state (7). 

This means you shouldn’t test intermittent eating regimes while training for the half marathon or marathon.

3. A 2017 review on the benefits and harms of intermittent fasting notifies of the possible risks of this dietary plan. The undue effects are: 

• mood swings
• extreme hunger
• low energy levels
• overeating on days without restricted calories
• obsessive thoughts about food
• irritability
• fatigue
• difficulty concentrating (14).

Besides all this, no matter how long you’ve been running or how avidly you’re good at it, you shouldn’t practice intermittent fasting if you are: 

• underweight
• have eating disorders
• suffer from type 1 diabetes
• have medication-controlled type 2 diabetes
• have undergone recent surgery
• suffer from mental health conditions
• have fever or illness (11).

Breastfeeding and pregnant women should abstain from any fasting regimen as well (11).

Read more: Running 3 Miles: Calories Burned, Weight Loss Success and Everything Else You Need to Know

Is fasted cardio real?

Indeed. It is a real thing that some people do. 

Fasted cardio entails working out on an empty stomach usually in the morning before your first meal. 

Here’s what it looks like. You wake up, brush your teeth, wash your face, put on a sporty garment, and start working out. You either go for a run, or trek to the gym for the bodyweight workout, or simply engage in physical activity at your house. 

After 30-40 minutes of training on an empty stomach you enjoy your healthy breakfast, whether it’s eggs, oats, or chicken with rice. 

Fasted cardio boasts both benefits and downsides. You have disclosed most of them in the previous segments.  

Please note that doing longer or more intense training on an empty stomach may be harmful to you. I recommend that you keep it to 30-45 minutes. Even 20 minutes of fasted cardio should be enough, as you keep your body moving therefore promoting your well-being. If you have any medical conditions or take medications, talk to your healthcare provider about doing fasted exercise to determine if it is safe or appropriate for you.

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The Bottom Line

Intermittent fasting and running: a winning combination or a terrible mistake? You have reached the end of this article and surely have your own conclusions about whether to run during fast or not. 

Let’s summarize all the aspects of this question to revise the mentioned points. 

If you want to combine running and intermittent fasting you should consider a couple of factors: your workout schedule and their intensity; the type of fasting; your body needs; and post-run recovery.  

Obviously, striving for harder fasting methods can negatively impact your running sessions as running itself requires a lot of power and endurance. 

However, once you pick up milder intermittent fasting methods, include a lot of protein and carbohydrate-rich food in your non-fasting periods, and stay hydrated, your chances to reap the potential benefits will rise.

Some athletes do intermittent fasting for good reasons: they feel it helps them trim more fat and promote endurance. Let me highlight that fasting may be vital for runners for its potential to reduce inflammation. 

There is a flip side though, as intermittent fasting isn’t perfect. It may actually provoke real side effects, such as dizziness, fatigue, irritability, mood swings, etc. 

By the way, most fasting plans might involve low-carb diets which are not beneficial for athletes. Pay attention to another thing – there are people who shouldn’t follow fasting regimes at all. 

Lastly, your health is your priority. I’m not the one to decide whether you should or shouldn’t include intermittent fasting in your running routine. Listen to your body, observe how you feel, and under no circumstances ignore pain or any other irritable feelings when running during the fasting period. 

In case you do, contact your healthcare provider and discuss your individual situation and goals with them.