Do You Run Faster on an Empty Stomach?


Runner

To say there are conflicting views out there on this topic would be an understatement. I have my own view but wanted to see what others thought so I did some research on this very important and practical topic to find out.

The professional opinion in both the medical and the sports fields tend to bust the myths of the “so-called” benefits of running or running faster on an empty stomach. They describe the real and practical benefits of at least drinking a glass of water before going on a morning run on waking up.

To help us answer our topical question, we will explore relevant information from a couple of sources in the medical, as well as the sports field. In particular, we will address the questions of whether is best to run on an empty stomach or is it better to run before or after breakfast.

I went out and conducted my own peice of original research to see what people thought. I asked 369 runners if they felt running on an empty stomach made them run faster. Here are the results:

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As you can see the majority (57.7%) thought that running on an empty stomach did make them faster. While just over a quarter were not sure, the surprising (and clear) takeaway from this is that on 16.3% thought eating DID make them run faster.


The pros and cons of running on an empty stomach?

There are more cons than pros to running on an empty stomach which is also called “fasted running.” Let us look at some of the issues that can arise when you run immediately on waking up from sleep. 

Your stomach has been on a fast for around 6 to 8 hours and in this condition, you go on your run. Your body needs fuel to do the running. It tries and draws on your fat reserves for this fuel, in the absence of any food in your stomach, to get the energy required. This is not sustainable for long. You cannot run faster on an empty stomach as fatigue sets in when your body demands more fuel from your fat reserves. As a result, your speed will slow down as you feel fatigue setting in. 

So, running on an empty stomach may lead to low endurance and lower speeds. It also increases the danger of physical injury.

You are more likely to feel tired as your energy levels decrease and the resulting fatigue may increase the probability of physical injury. This could be possible due to a lack of attention to hazards within your immediate surroundings. Most importantly, your brain may be starved of glucose which is necessary for it to function optimally, as all the glucose is diverted to fuel your hard-working muscles. It becomes more difficult to pay attention to what is happening around you.

Not only does it increase the possibility of injury but “fasted running” may also increase muscle loss and consequent weakness. Your adrenaline glands, located on top of each kidney in your body, manufacture a hormone called cortisol. These are responsible for the blood glucose and stress-response functions in your body. Cortisol levels are highest when you run on an empty stomach in the morning, and this results in the protein breaking down in the cells of your muscles, negatively affecting them.

Running on an empty stomach also is not effective for weight loss, over the long-term. No doubt, your body burns more fat during “fasted running” and less glucose. But it automatically compensates after your exercise and decreases fat burn during the course of your day for more glucose.

If you suffer from Diabetes, whether type 1 or 2, running on an empty stomach increases the risk of lowering your blood sugar to dangerously low levels. So, it is not best not to do this.

Having now understood why we should not run on an empty stomach; we will now concentrate on our next dilemma.

Which is better, to run before or after breakfast?

People who believe in exercise or going for a run early in the morning on waking up are divided loosely into two groups. 

One group believes in eating a light breakfast and then going for a run, while the other group insists on first finishing their run and then having a proper breakfast. 

Some early morning runners who exercise without breakfast may have a glass of water before they leave home for their run.

Without any detailed analysis of both the groups, we can probably assume that the light-breakfast eating group will certainly have some energy during the run. Their bodies will have a readily available sources of fuel for their exercise.

In the 2014 study described in the Journal of the International Society of Sports Nutrition reveals that while we are running, our bodies consume energy. This energy is derived from two main sources. Fat and Carbs. If the study participant had breakfast before commencing the run then they burnt more carbs as compared to the ones who commenced on an empty stomach who burnt more fat. 

Practically, if you are aiming to lose weight by burning the fat in your body it may not be worth running before breakfast. You will be uncomfortable and so hungry that you may end up eating more than you normally eat after your run, and thus negate your goal of losing weight.

An important fact to remember when you are exercising is that your body burns energy sources in a particular order or preference. First, it sources its energy required by burning carbs followed by fat and then lastly the proteins obtained by breaking your muscle mass.

Glucose is the simplest form of carbs which are the primary source of energy for your body when exercising. Glucose is readily available to the muscles as it is very easily absorbed by our bodies. Your muscles start burning fat once your carbs are depleted. A huge disadvantage if you run before you have had breakfast is that you may end up probably, losing some muscle mass. Your body is more likely to break down the proteins in your muscles to release the energy it needs to fuel the running exercise since it does not have any carbs to burn and your fat reserves may be already depleted.

It may be interesting to put in a couple of fasted runs into your week after light breakfast. This probably will give your body a chance to start burning fat, at least a couple of mornings during the week.

In this way, your body can “learn” to try burning fat at least for a couple of days weekly, while it has a chance to burn carbs first before fats on the other days of the week. An important consequence of doing this may be that your body’s chances of breaking down your muscles to access the protein molecules within will be nullified. Thus, you may minimize any muscle breakdown possibilities attributable to your morning runs.

Remember that slow and steady wins the race. So, running consistently at a pace comfortable to you is healthier than running fast. To keep yourself motivated, you can track your general progress of how much calories you have burned during your walk or run by using a handy calorie burn chart, like the one found below.

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Takeaway

So we still don’t have a clear answer, given that the runners in our research thought they did run faster, the science isn’t there to support this.

On empty stomachs, after fasting for over 6 to 8 hours while asleep, we will not have enough fuel for our body to produce the energy, to run faster. There are no carbs for the body to burn and derive the energy it needs to fuel the exercise.

There are some downsides to our health and well-being if we force our bodies to run faster over a period of time, while on empty. Notable among them are constantly feeling fatigued through the day, possible exposure to hazards while out on your run, losing muscle mass, and self-defeating the goal of losing weight in the long run.   

It may be possible to mix a couple of mornings with no breakfast and most other mornings with breakfast, during the week. This may help you to arrive at an optimal running schedule that just might work subjectively, for your body.

Mark Norman

I've been running for over 6 years and now try to balance it with life as a dad to two young kids. I'm not super quick, I just try to run consistently, not always easy! I'm lucky enough to have run the London Marathon twice along with countless other half marathons and 10ks. I'm also one of the Run Directors at my local parkrun.

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