Many people believe that exercising on an empty stomach is one of the best ways to speed up their fat loss as the body will have to use fat for fuel as the body is deprived of glucose to fuel their workout. With the rising popularity of using intermittent fasting as a dietary method this belief has increased even more in recent years as many people adopt fasting before working out. While there does appear to be some benefits to doing this it is not without some drawbacks that could counteract any benefits it may provide. Once again there is no definitive answer to this question as it really depends on several factors unique to each person. In this article, I will look at the pros and cons of using this eating strategy so you can determine if it is best for you.

What Are The Benefits Of Exercising on An Empty Stomach?

Firstly, I will say that I have always found it difficult to exercise on an empty stomach and feel my training efforts are severely compromised if I am hungry before I even begin. If I am going to work-out in the morning I will make sure I eat breakfast beforehand or at least have some food on hand if I get hungry. Due to the fact I personally felt crap when I exercised on an empty stomach led me to believe that everyone should eat beforehand, but over the years I witnessed many people thriving working out on an empty stomach.

Forcing someone to eat beforehand who is better off with an empty stomach may backfire and make them sluggish and even nauseous. It is important to recognize that there is no one method everyone should follow with regards to nutrition or exercise and to acknowledge that we are all unique in how we digest and metabolize food. Even the type of food to eat before you workout can make a difference for those who do like to eat before exercise.

Before I discuss the various benefits of eating in a fasted state just remember this may not mean it is great for you to do even though the benefits sound encouraging. The only way to be sure is to test it out to see if it works or not.

Let’s look at two of the main benefits.

Fasting Before Exercise May Help You To Burn More Fat

A fasted workout is a workout you do in a fasted state (at least four to six hours after eating). When fasted, your body has had time to digest and metabolize a good proportion of what you ate at your last meal. This means your body will use prefer to use fat instead of glucose as its fuel source for providing energy to complete your workout.

Hormones like insulin and glucagon constantly change when we eat food in relation to the amount of glucose in the blood and liver. When blood glucose is high, the body will prefer to use glucose as its fuel source as it is a simple process for the body to convert into energy. Glucose is found mostly in carbohydrate rich foods. When your blood glucose levels are low, the body will switch to a fat burning method to preserve the glucose stored in muscle and the liver. This helps maintain an optimum blood glucose level so you don’t go into an energy crash.

This is where exercising in a fasted state tries to take advantage of the way the body burns fuel for energy in order to optimize the amount of fat burned during an exercise session.

Several studies have confirmed that when you exercise in a fasted state, insulin sensitivity increases and so does production of growth hormone. Both of these can boost fat loss, which supports the argument that fasted exercise results in more fat loss.

Reference:

Kim TW, Lee SH, Choi KH, Kim DH, Han TK. Comparison of the effects of acute exercise after overnight fasting and breakfast on energy substrate and hormone levels in obese men. J Phys Ther Sci. 2015;27(6):1929–1932. doi:10.1589/jpts.27.1929

This is very similar to the Keto diet that also deprives the body of carbohydrates in order to use fat as its preferred fuel source. A person already using the Keto diet will often be using intermittent fasting in combination with this eating method and may be perfectly fine exercising on an empty stomach. as their body will be very efficient at using this process.

However, someone who still eats carbohydrates may find this much more difficult to do and their energy levels may be compromised significantly. Even those on the Keto diet may suffer if the type of training completed requires high intensity efforts like maximal strength training or interval training.

More on this shortly.

Fasting Before Exercise May Assist Autophagy

The second benefit that may have an effect of exercise on an empty stomach is it may assist the body in the process of what is known as Autophagy. This is a natural, self-preservation mechanism whereby the body removes damaged or dysfunctional parts of a cell and recycles other parts toward cellular repair.

Autophagy is the body’s way of cleaning out damaged cells, in order to regenerate newer, healthier cells. “Auto” means self and “phagy” means eat. So the literal meaning of autophagy is “self-eating.”

While this sounds like a bad thing, it’s actually beneficial to your overall health and has been shown to be very beneficial as a way to remove toxic proteins from the cells that are attributed to neurodegenerative diseases, such as Parkinson’s and Alzheimer’s disease.

This refolding process is one of several factors that need to work in order for your brain to function. Importantly, fasting activates autophagy, which is your body's way of taking out the trash, and will also trigger the regeneration of stem cells.

Used in combination with your exercise it can be a powerful way to combat the onset of deadly chronic diseases like Alzheimer's disease which continues to be a leading cause of death in many countries around the world. In the U.S. statistics show 1 in 3 seniors die with Alzheimer's or dementia — more than the number killed by breast and prostate cancers combined!

As we get older the cells in our body gradually lose their ability to cope with stress. As the damage builds up the immune system is activated and sends in white blood cells to clean up the dead cells, which creates inflammation. If the damage becomes chronic it creates even more damaging proteins which are the very ones linked to the development of Alzheimer’s.

With regards to the brain when neurons get worn out from excessive cellular stress they eventually erode and sever the connection. Losing a signal here and there is not a big deal as you are constantly making new ones connections and rewiring yourself from stimulation of daily living and problem solving. Problems arise when the decay outpaces the new construction.

This is why it is so important to ensure your brain is receiving constant stimulation on a daily basis as you age to ensure your brain is restoring more damaged cells.

And this is where exercise can become extremely beneficial for it not only prevents the brain from rotting, it also helps to reverse the deterioration with aging by providing the brain with the stimulus it needs to build new cells and outpace the loss of damaged ones.

This is something I discussed in great detail in this article – How to use exercise and nutrition to prevent dementia.

It is not just dementia and Alzheimer’s that can benefit from this as more recently the role of autophagy in preventing or treating cancer has attracted a lot of attention. Although there is limited research or scientific evidence to support this at this stage there is a possibility it could be something of good value.

Based on these two benefits alone it seems like a no-brainer that you should try to workout with an empty stomach. However, once again it is not quite that simple as there are a few drawbacks that you need to consider and it could even be counterproductive to your health.

Let’s take a look at the drawbacks before you decided if this is good for you.

Fasting May Significantly Compromise Your Workout Performance

While there appears to be some compelling arguments for completing your workout in a fasted state it can greatly compromise your training ability. Over the long term you may struggle to achieve the results you are looking for and you may even lose some muscle!

This is because when you exercise intensely in a fasted state, your muscles can degrade. This is because your body pulls apart amino acids to help preserve critical blood glucose. Also, chronic low blood glucose and rising cortisol (stress hormone) levels can depress the immune system.

The type of exercise you are completing makes a big difference here. For example, if you are just going for a 60 minute walk or doing some light cardio you will most likely be fine. However, if you are intending to do a high intensity strength training or interval training workout there is a good chance you are going to struggle.

We all know that to in order to maximize your strength training efforts it’s crucial that you get close enough to failure during your sets to still maximize growth. It can be near impossible to do this if you are in a famished state and your body is running on fumes.

This explains how I feel whenever I have tried to complete workouts with no food in my stomach. At first I feel okay but the minute I really push it, especially with tiring leg exercises like squats, deadlifts, and lunges I can feel my body become weak and lethargic. Anything I do after I feel like this is incredibly weak and sluggish until I can eat something again. Even then it may take a bit of time for my body to absorb the food and for my energy levels to restore to optimal levels.

This is also the same feeling I would experience when I did not eat enough food during a long endurance event like cycling. I used to regularly compete in 130-200km cycle events and I knew I had to regularly eat during these rides every 60-90 minutes to keep my glycogen levels topped up and avoid “hitting the wall”. The minute you felt hungry you knew you were in trouble as it was too late and your body would dramatically lose all your energy and effort as your body was running on fumes.

Even though you can use your fat stores for fuel it does not provide the same intensity and explosiveness that glucose can, so if your goal is to improve your training results this type of eating strategy will be counterproductive to your goals.

This is where those who play sports will know exactly how important eating good balanced nutrition before their competition or training can be. This has become a real science in itself as many professional athletes look to find the best times to eat to fuel performance and recovery. You can read more about this in the article – Can you improve fitness without losing strength gains?

Eating too much beforehand or eating too close to your training can make you feel sick as the food sits in your gut. The best strategy to avoid this problem is to eat two hours before your strength workout. If you like to exercise first thing in the morning you might have to have something small like a banana or a small piece of toast with peanut butter to get you through.

A mix of carbohydrate and protein is an excellent choice before weight training.  The carbohydrate gives your body some fuel to enhance performance, and the protein helps your body build muscle in your recovery phase.

By eating a small snack prior to a workout, you can still encourage the fat-burning process without depriving your body of necessary fuel. You also need some calories, protein, and carbohydrates after your workout to help your muscles recover and get stronger.

Fasted Workouts May Do Very Little For Long Term Weight Loss Results

This is where it gets really interesting.

We all want to have a nice flat stomach for besides the obvious benefit of looking good we know there is many great health benefits associated with less belly fat. Excessive visceral fat is linked with many diseases due to its location being so close to many vital organs, such as the pancreas, liver, and intestines. The higher the amount of visceral fat a person stores, the more at risk they are for certain health complications, such as type 2 diabetes and heart disease.

Sometimes in our quest to get rid of excessive weight people resort to the quick fix or the easy route instead of getting themselves prepared for the long haul.

While there is some evidence showing potential benefits of exercising fasted, there is no strong evidence that fasted exercise leads to greater weight or fat loss.

Reference:

MDPI and ACS Style Hackett, D.; Hagstrom, A.D. Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis. J. Funct. Morphol. Kinesiol. 2017, 2, 43. https://doi.org/10.3390/jfmk2040043

You have to remember how much fat and glucose is used as fuel is prioritized over a 24 hour period in relation to ALL energy demands, not just those during your workout. You may burn some extra fat during a fasted exercise session, but it is not likely to be enough to burn a lot of stored fat when considered overall.

This is particularly true if you tend to over-eat after the session because you are so ravenous and hungry or if your nutrition habits for the remainder of the day are not up to scratch. Any weight loss you may have obtained earlier in the workout could easily be erased by these poor eating habits you have not yet corrected.

Another factor consider is physical inactivity. The effectiveness of your workout is minimal at best if this is all you do for the entire day. In the book “The Obesity Paradox” the author claims our obesity problems may have more to do with physical inactivity than excessive eating. A study by Dr Timothy Church from Pennington Biomedical Research Centre in Baton Rouge showed in a 2011 paper that the dramatic drop in energy expenditure in work related activities over the past 50 years explains the increasing prevalence of obesity in the same time period.

If you worked out for 30 minutes per day and the rest of your day you sat down, your total activity percentage of available time to move might be only 4% at best! In this example, the 30 minute workout while it is great to do and has some amazingly positive aspects, is pretty much cancelled out by the negative impact on the metabolism by the 96% of sedentary activity the rest of the day.

You can read more about this in the article – What is better for weight loss, exercise or nutrition?

The last factor to consider is the impact on your health and immune system that a fasted workout may create. There are many people keep who keep bouncing from normal blood sugar to low blood sugar levels during the day and constantly exposing their body to hypoglycaemia. This roller coaster effect can be disastrous to the body and the rebound effect is that if they eat too close together to compensate, that they overload their body with too much food. This puts tremendous stress on the body which has to activate the immune system to cope with the stress.

Those people who suffer with Diabetes know all about the dangers of blood sugar levels and will avoid fasted workouts for this reason. The underlying problem in type 2 diabetes is improper insulin and leptin signalling. In type 2 diabetes, your pancreas is still producing some insulin, the problem is that there is usually too much being produced on a chronic basis, and as a result your pancreas is unable to recognize the insulin and use it properly.

Additional Resources to Help You with Exercise & Nutrition

Obviously, there is a ton of information I have not included in this article with regards to healthy eating and exercise so to help you out there are some great reports you can instantly download that include everything you need to know about getting in great shape. You will find the PDF reports shown below, that you can instantly download, will provide you with the complete plan for combining healthy eating with exercise, and this applies to people of all ages.

Summary

As you can see the answer to the question of whether to eat or not before training is not that simple. There are a lot of pros and cons consider and each person has to determine which option is best for you. Some people may do very well with this and that is fine, but many try to force this on their body and it may be more detrimental than useful.

I see great benefits for this strategy with the older adult with regards to autophagy and the prevention of Alzheimer’s and dementia. The fact that most of the older adults do not workout at extremely high intensity or need to eat that much food either makes the drawbacks much less of a concern. The benefits for this population outweigh the drawbacks.

If your training performance means a lot to you, or if you compete in sports this is not likely to be a good strategy and you will be better off eating before you train. A combination of protein and carbs 2 hours before your workout is perfect.

Lastly, if your goal is weight loss I would try to make all the changes in other areas first before trying to use this as another way to help you drop the extra kilos. I would like to see someone workout to their optimal level and be able to keep their nutrition and lifestyle habits in check for the entire day rather than relying on a fasted workout to speed up the results.

The only way to know for sure is to test it yourself and see.

For more ideas and information on specific topics I may not have covered in detail be sure to check out our INDEX PAGE on the website that has over 300 of our best articles. These are all sorted into categories for quick reference so you can find what you are after more easily. You can also subscribe to our FREE fortnightly newsletter by clicking here.

If you live in Melbourne and feel you need specific help with your exercise program please feel free to reach out to me for help and we can set you up with your individualised program. 

About The Author

Nick Jack is owner of No Regrets Personal Training and has over 18 years’ experience as a qualified Personal Trainer, Level 2 Rehabilitation trainer, CHEK practitioner, and Level 2 Sports conditioning Coach. Based in Melbourne Australia he specializes in providing solutions to injury and health problems for people of all ages using the latest methods of assessing movement and corrective exercise.

Additional References:

• The End Of Alzheimers by Dr Dale Brederson
• Dementia Australia
• Precision Nutrition
• Obesity Paradox - By Carl J. Lavie M.D.
• Movement - By Gray Cook
• Bending the Aging Curve -  Joseph Signorile
• Athletic Body in Balance - by Gray Cook
• How To Eat, Move & Be Healthy by Paul Chek
• Heart foundation
• CSIRO
• Nutrition & Physical Degeneration - By Weston A Price
• Big Fat Lies - By David Gillespie