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Home arrow Fitness arrow Running arrow Intermittent Fasting and Running: Can You Run While Fasting?

Intermittent Fasting and Running: Can You Run While Fasting?

Written by Isabel Mayfield
Fact checked by Rosmy Barrios, MD
Last update: May 10, 2023
14 min read 1585 Views 0 Comments
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Combining intermittent fasting and running can help you lose weight. But it’s important to weigh the benefits against the risks.

intermittent fasting and running

Can intermittent fasting and running help you lose weight faster without risking your health? Or affecting your performance?

You can fast to reduce body fat and acquire a leaner body. According to some studies, you may even boost your running performance.

But simply skipping meals isn’t the best way to go about it. You have to get intermittent fasting and running right for them to work. Otherwise, you may only damage your body.

Read on to find out what intermittent fasting for runners is. Discover the benefits of time-restricted eating while running and tips to get it right.

What Is Intermittent Fasting?

Intermittent fasting limits your eating schedule. You eat only during specific eating windows. You then follow a fasting period.

Intermittent fasting is not a type of dieting. When you fast intermittently, you don’t restrict what you eat. Rather, you restrict when you eat. You may find intermittent fasting easier than dieting.

It may show better results than following a diet. As many as 95% of people who lose fat mass through dieting gain it back.

Most fasting methods don’t come with an energy intake cap either, though some do. Popular intermittent fasting strategies come with a different fasting schedule:

  • 16:8 intermittent fasting method – Fast for 16 hours and then eat during an 8-hour eating window every day. You may have to skip breakfast or dinner.
  • 5:2 intermittent fasting method – Eat only 500 calories a day for two non-consecutive days of the week. Men can eat 600 calories a day. Eat normally during the other days. For example, eat only 500 calories a day on Monday and Friday.  
  • Eat stop eat method – Fast for 24 hours at a time on non-consecutive days. You may, for instance, fast on Saturday and Wednesday. On the other days of the week, you eat normally.

Intermittent fasting strategies promote a caloric deficit. They encourage a lower caloric intake without necessarily limiting it. Since you eat less often, you take in fewer calories than your body needs. So your body starts burning stored fat instead.

Important: Making healthy food choices is crucial to intermittent fasting and maintaining lean body mass. You can’t go on a fast food spree during your eating window. Not without risking your health.

General Health Benefits of Intermittent Fasting

Intermittent fasting was developed as a weight-loss strategy. But the health benefits of intermittent fasting go beyond losing weight. Here’s what science has to say about the general advantages of intermittent fasting.

Lowered insulin levels – A 2016 study found that alternate-day fasting reduced insulin levels. It also led to improved insulin resistance. Reducing insulin resistance triggers fat burning and promotes fat loss.

Increased human growth hormones – Intermittent fasting boosts levels of the human growth hormone. This helps reduce fat, repair muscles after a run, and maintain healthy tissue. It also supports metabolic health and stable blood sugar levels.

Cellular repair – Intermittent fasting studies show that fasting initiated cellular repair. Among other processes, cellular repair involves removing waste products from cells. It also helps decrease inflammation in the body and supports the immune system.

Improved cardiovascular health – Intermittent fasting may reduce high blood pressure, bad cholesterol, and blood glucose levels. A 2020 study highlights the potential heart health benefits of fasting.

Better gut health – Skipping late meals and fasting overnight may promote gut health. With intermittent fasting, this becomes easier. Intermittent fasting can also help you avoid disordered eating, which may harm your gut.

Significant weight loss – A 2017 study found an association between intermittent fasting and weight loss.

The general health benefits of intermittent fasting look promising. But as a runner, you need more calories than the average sedentary person. So how do intermittent fasting and running square?

Is It Normal to Practice Intermittent Fasting for Runners?

When you fast as a runner, you run the risk of ending up with depleted glycogen stores. This will make you feel tired and affect your performance. That said, several studies show that intermittent fasting for runners may have benefits.

When you run, you can burn around 80 to 140 calories per mile. The exact amount varies from person to person. Your running pace, weight, and gender can influence this.

Marathon training, for instance, can be very demanding on your energy reserves. The same is true even for shorter events, like half-marathons or 10k.

Runners need a diet high in carbohydrates to get enough calories. The body transforms carbs into glucose for immediate energy. This is necessary for cell metabolism.

The body stores excess blood glucose in the liver as glycogen or turns it into fatty acids. When you run long distances, your body taps into liver glycogen reserves for energy.

Like fuel in a gas tank, stored glycogen comes only in a limited supply. If you don’t take in food, your body cannot restore this supply.

3 Benefits of Running While Fasting

Increased fat burning and better endurance are the key benefits of running while fasting. Here’s what science has to say about them.

#1 Improves endurance

A small study found that training in a fasted state may lead to improved endurance. But it’s important to note that the study involved only males. The training occurred over 6 weeks.

Meanwhile, a more recent meta-analysis concluded that intermittent fasting might increase VO2 max. VO2 max is the maximum amount of oxygen you breathe in as you exercise at the highest intensity. A high VO2 max is important for endurance runners.

Long-distance running relies on aerobic energy. Your body essentially combusts carbs and fats in the presence of oxygen. Without an adequate supply of oxygen to the muscles, your running pace will drop.

#2 Increases fat burning

A 2013 study noted that intermittent fasting may help endurance athletes burn fat faster. The male runners in the study ran at a moderate intensity.

However, fasting increases appetite after exercise. Also, energy balance post-exercise was the lowest in fasters. If you plan on fasting before exercising, you may experience a big energy dip after.

What about the long-term impact of fat burning in a fasted state? Over time, training your body to use more fat may actually promote the storage of intramuscular fat. Never underestimate your body’s ability to adapt!

#3 Helps to avoid digestion problems

Problems with runner’s stomach? A runner’s stomach happens when you run on a full stomach. Symptoms may include bloating, cramping, nausea, vomiting, and diarrhea.

Eating a large meal before a run might cause vomiting and other digestion problems. But why exactly does this happen? When you run, your body redirects blood from your stomach to your cardiovascular system. This can affect your digestive system.

Fasting before a run can prevent problems with your digestion. It can also make you feel lighter. If a runner’s stomach often bothers you, intermittent fasting may help.

3 Drawbacks of Running While Practicing Fasting

Running in a fasted state may feel harder than normal. It may also increase your risk of injury and lead to muscle tissue loss.

If you’re on the fence about eating versus fast, that’s only normal. Knowing about the drawbacks of fasting and running will help you make the right decision.

The disadvantages of running while fasting can be serious, as any running coach would point out. Let’s zoom in on them to better understand them.

#1 Harder to run

Completing a long or intense run on an empty stomach can be a challenge. All the more so if you’re aiming for a good finish.

When you fast, you don’t get in any calories. Your body has to draw on energy reserves. This includes liver glycogen and energy stored in your other tissues.

Your body may still have enough energy to run. (Unless, of course, you have been fasting for days.) But you may have heavy feet and struggle to perform at your best.

Your body will direct available energy reserves to maintain essential body systems. Much like a driver going slow in third gear to reach the destination.

Shifting to fourth gear and increasing the speed would burn more fuel and decrease fuel economy. The body works in a similar way.

A 2020 review article recommends that runners avoid high-intensity training while fasting. Note, too, that when you run faster, you burn more calories.

#2 Injury risk

Even on a healthy diet, running puts stress on your body. Unbalanced muscle groups or poor running form can lead to injury. You have to do your best and rest.

Fasting while running can compound the risk of injury. A low-calorie intake can take its toll on your bones. More specifically, it can hamper new bone formation.

Bone is living tissue and constantly renews. In a process called remodeling, fresh bone tissue replaces old bone pieces.

Soft tissue may also suffer. Your body needs protein to repair muscle damage after runs and workouts. Intermittent fasting is likely to reduce your protein intake. It may also limit your nutrient intake. Together, these can affect your body’s ability to renew itself.

Giving your body enough rest when fasting and running is important. But remember that your body needs more than rest. It needs calories, proteins, and nutrients to repair itself. Intermittent fasting is not an excuse to avoid a healthy eating regimen!

#3 Leads to loss of muscle mass

Muscle wasting is another risk that comes with fasting and running. Not eating when you’re hungry can make it difficult to get enough protein from your diet.

This is especially true for long-distance running. A 2016 study found that amateur marathon runners suffered muscle damage.

Even endurance athletes who eat normally sometimes struggle with muscle wasting. Endurance running makes big demands on your body. And that includes your muscles.

When running long distances, it’s crucial to take in protein to support muscle building. Endurance runners need between 1 to 1.6 grams of protein per kilogram of body weight every day. Your weight, gender, body composition, and other factors may affect this.

Ever noticed how marathon runners tend to have lean rather than ripped legs? Long runs may eat into your muscle even if you eat plenty of protein.

8 Tips for Runners During and After Fasting

Thinking of giving intermittent fasting a go? Hydration, sleep, and eating the right foods are all important. Neglecting any of these may undermine your attempts to reduce weight fasting. It may also affect your health.

Here’s how to stay healthy and avoid injury and exhaustion during an intermittent fast.

#1 Stay hydrated throughout the fasting period

An intermittent fast doesn’t mean not drinking water. A human being can survive for weeks without food. But only for about three days without water.

Your body needs water to maintain essential functions. When you run, you lose water through sweating. You also lose electrolytes, key minerals your body needs to function well. Losing electrolytes can result in cramps and other symptoms.

Make sure you drink enough water during your fasting period. If you run in the morning, drink at least one glass of water before you head out. Take a water bottle or hydrating drink with you. Keep yourself hydrated during the run.

In the end, listen to your body. This is the best strategy to ensure you stay hydrated. Drink when you are thirsty. You may put off hunger and skip a meal. But you should never run thirsty. That’s not supposed to be part of an intermittent fast.

#2 Sleep enough to lose weight in a healthy way

Getting at least 7–8 hours of sleep every night will help your body recover. During exercise, muscles break down. Undisturbed sleep after intermittent fasting helps muscles repair.

The good news is that intermittent fasting may help you sleep better. Subjects in a pilot study reported better sleep quality. They also said they had more vigor and better daytime concentration.

If the intermittent fasting method you follow interferes with your sleep, reconsider it. As a runner, you can skip meals and reduce your calorie intake. But you shouldn’t be stingy with your sleep.

Sleep deprivation will affect more than your running performance. It can lead to many chronic health problems. These include heart disease and depression.

#3 Avoid reaching personal goals while fasting

Running in a fasted state is likely going to affect your running performance. This is true if you run in the morning after having fasted all night.

If you also did not eat dinner the night before, the impact may be even stronger. Your body will not have received energy for 10 or more hours.

What’s more, exercising in a fasted state in the morning can hamper weight loss. More about that in a bit.

The bottom line here is that if you do intermittent fasting and running, you shouldn’t push yourself too hard. You’re not in the right state to improve personal records.

Instead, you’re sacrificing some of your running performance to try to burn more fat. Since your fuel tank is not full, run at a comfortable pace. Your running coach would more than agree.

#4 Run at the right time

In the morning, cortisol levels are high. When you run or exercise, you put extra stress on your body.

Your body may overuse sex hormones to make more cortisol, one of the stress hormones. High cortisol levels promote fat storage. This may work against your weight loss goals. 

You may find running in the afternoon easier. But it all depends on your eating window. For example, you can eat a healthy, carb-rich breakfast followed by lunch. These meals can fuel a good run in the afternoon.

#5 Watch out for supplements to maintain a lean body mass

Food supplements may break your fast without you realizing it. Gummy multivitamins that contain pectin or maltodextrin have sugar and calories. These increase blood sugar levels and disrupt intermittent fasting.

To get the full benefits of fasting, avoid foods or supplements that trigger an insulin response:

  • Supplements containing polysaccharides. Common culprits include pectin, maltodextrin, and fruit juice concentrate.
  • Branched-chain amino acids. BCAAs may increase insulin resistance. You’ll often find them in running supplements.
  • Protein powders. These, too, have calories. Even if you only drink them with water, your body will exit fasting mode.

On the plus side, you can still take supplements without sugar and calories. Safe choices that should not increase your blood sugar levels include probiotics, algal oil, and multivitamins.

Always check the label to be sure. Even individual vitamins may contain fillers that trigger an insulin response. Also, keep in mind that you need to take vitamins E and D with food. Else your body won’t absorb them properly.

#6 Break a fast with the right foods for weight loss

Fasting isn’t only about refraining from eating. It’s also about eating the right foods when the eating window opens. An empty stomach handles some foods better than others. Especially after a serious calorie restriction.

Avoid eating foods high in fat, sugar, or fiber straight after fasting. Foods to avoid include burgers, cake, cookies, chocolate snacks, and soda. They may cause abdominal discomfort and bloating. They may also spike blood sugar levels.

The best foods to break a fast with are rich in nutrients but easy to digest. Break your fast with:

  • Smoothies. You can add protein powder to your smoothies for a healthy dose of nutrients. They will remain easy to digest as they have less fiber than whole foods.
  • Soups. The best soups for breaking a fast have carbs that are easy to digest. Think tofu or lentil soup.
  • Steamed or boiled vegetables. Sweet potatoes and other starchy veggies provide energy. They are also gentle on your stomach.
  • Eggs. Eggs are nutritious and have healthy fatty acids. Boiling eggs helps retain more nutrients than frying them.
  • Kefir or yogurt. These fermented foods have protein and calcium, which are good for your bones. They may also promote a healthy gut microbiome.
  • Dried fruit. Try dates, raisins, or dried apricots. But avoid overeating dry fruit. Soft, chewy foods can promote tooth decay.

After breaking your fast, eat healthy foods that provide enough carbs, protein, and healthy fats. These should complement your last meal and provide a balanced nutritional intake.

Once you become used to intermittent fasting, your stomach may tolerate other foods more easily.

#7 Watch your portions

It may sound contradictory, but intermittent fasting may actually promote eating. All that fasting may leave you craving food badly, leading to weight gain.

Overeating during your eating period may work against your weight loss goals. Avoid it by limiting your portions. Also, eat slowly and mindfully to give your body time to feel satiated.

Your last meal of the day should never be heavy. During intermittent fasting, planning your meals can help you stick to your portions. It also promotes a balanced dietary intake.

#8 Track your performance before and after fasting

What impact does intermittent fasting have on your running performance? And is this manageable enough to keep on fasting? The only way to find out is to track your performance.

Tracking your progress is one of the key steps to becoming the runner you want to become. And shed any extra pounds without risking your health in the process.

A Word From Our Expert

Intermittent fasting and running can work together to help you burn fat and lose weight. But it may also affect your running performance. This is especially true for long and demanding races.

Fasting and marathon training don’t square. But if weight loss is your number one goal, you could give intermittent fasting a go. Don’t do intermittent fasting while training for a marathon or any endurance event. You will stress your body and invite injury.

Start small with a safe fasting approach like 16:8. This intermittent fasting method allows you to fit in 2–3 hearty meals during your eating window. To accustom your body to fasting, you can do it first on days when you don’t run or exercise. That may make it easier.

But don’t go all out. Run comfortable distances. And don’t expect to beat your personal records. As a runner, you need calories to power you up.

In the end, pay attention to the cues your body gives you. If intermittent fasting leaves you feeling drained, try a different method. Or simply eat regular meals.

Fasting and running shouldn’t feel like a big struggle. If it does, it may not be for you. Don’t put your health at risk!

Key Takeaways

Intermittent fasting for runners can work. But it isn’t a magic solution to losing weight. It may help you burn excess fat, but it has risks.

  • You can do short and light workouts during intermittent fasting.
  • Don’t do long runs or workouts in a fasted state. After prolonged fasting, you are not in high performance mode.
  • Break your fast with gentle foods and get enough sleep.
  • Try different intermittent fasting methods like 16:8, 5:2, and the eat stop eat method.
  • Listen to your body to find the eating pattern and caloric restriction that works best for your running goals.
Written by Isabel Mayfield
Isabel Mayfield is a certified yoga instructor with over 10 years of experience in the fitness industry. She is passionate about self-improvement and loves to help people improve their sense of self-worth through education and support in meeting their fitness goals.
The article was fact checked by Rosmy Barrios, MD
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Written by Isabel Mayfield
Fact checked by Rosmy Barrios, MD
Last update: May 10, 2023
14 min read 1585 Views 0 Comments

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