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  • Writer's pictureSteve Cronshaw

Is Morning Fasted Exercise Beneficial?

Updated: Apr 5, 2022

Should you undertake morning Fasted Exercise?

Some Science behind Fasted Exercise.

If you had asked me five years ago, whether going out on the bike in the morning without breakfast in a fasted state was beneficial, I would have said “NO way. DO NOT do it!"

I would have gone on to tell you the disadvantages far out way any benefits - muscle wastage, blood sugar lows, and eating the entire contents of the fridge on returning from the ride, are things that would concern me then.

However, after studying the science, I have completely changed my mind. Over the last two years, I have been researching the subject on my Sports Nutrition M.Sc. and the science has convinced me that there are definitely benefits to be gained from fasted exercise for most athletes. There are also equally important reasons for non-athletes to undertake this practice, however, there are good ways to do it and ways NOT to do it.

Note. I do NOT recommend fasted rides at your functional threshold power (or FTP heart rate) and defiantly not for high-intensity rides. I consider it to be counterproductive for those types of rides/training sessions when good carbohydrate availability is beneficial for the best outcomes.

In this article, I will look at the science and try to demystify it, to look at the benefits for all of us to gain some advantages.

Firstly let's start with a definition of what is a "fasted training session", it is defined as completing a morning training session following an overnight fast and before breakfast (Burke et al. 2018)

Additionally, let me say if you are a young, fit, slim, elite, endurance athlete around 20-years of age, then the benefits are not going to be as pronounced, but there are still benefits to be had for this group.

On the other hand, if you are someone who is trying to lose weight, a masters athlete, or someone simply attempting to improve your aerobic endurance then read on, as this is definitely for you because you can undoubtedly get more “bang for your buck” in doing aerobic exercise and improved body composition occasionally in a fasted state.

A reminder first of how we produce energy for sport and exercise. Our bodies should be flexible enough to obtain energy from multiple sources, the food we eat, which will be mainly carbohydrates and fats. Additionally, there is protein, but this is a convoluted route to producing energy from it.

More, energy comes from stored sources, this is the glycogen in our muscles and liver, from circulating essential fatty acids in our blood, and from our bodies own fat reserves. And this last one - our own fat reserves - will for most people provide enough fuel for them to go for days and that is true even for very lean athletes.

Ex-pro cyclist and now a mitochondria researcher Dr Iñigo San Millán who also coached Slovenian cyclist Tadej Pogačar to his 2020 Tour de France victory have produced lots of research in this area. He has validated the blood lactate testing method that I carry out, and a good research article on this subject is the San-Millan and Brooks (2018) as below.

Three Benefits of Fasted Exercise

1. Metabolic Flexibility

What’s that you ask? Well, it’s our body's ability to produce energy from different fuel sources depending on what is available. Most people these days, whether they are athletes or not, consume large quantities of carbohydrates. Carbohydrates are essential for very top-end performance. Nothing wrong with this, you say! But yes, there can be if you are not in an energy balance and the obesity epidemic illustrates this.

Even for fit athletes, if they over-consume carbohydrates and sugar, then over the years and decades they build up a condition called insulin resistance which creates a dependency on glucose for energy. This condition increases blood sugar levels and fluctuations that in turn, make the body release more insulin to bring down the blood sugar levels. Our bodies are designed to only have a teaspoon full of sugar in our blood at any one time, so the surplus blood sugars should go into our muscles and liver to store it for energy. Once we have this condition of insulin resistance, then our bodies are not very efficient at storing it in muscles and the liver due to the high insulin levels. These high insulin levels are very effective at driving this blood sugar “wham”, straight into our fat cells for storage.

When we have continuously high blood sugar levels and high insulin, then the hormone insulin prevents us from accessing energy from our fat cells and makes us ever more reliant on carbohydrates for fuel. The result can be an increasing accumulation of fat around our middle, energy highs and lows, and a decreased desire to exercise.

2. Mitochondria Biogenesis

This is the process by which cells increase Mitochondria mass. Mitochondria are the power plants in our cells and muscles that produce the energy to power our aerobic energy system. Improving our aerobic conditioning is mostly about endurance training that induces higher mitochondrial content levels; a benefit of this is leading to higher glucose uptake by our muscles.

When we train in a fasted state at the zone-2 intensity with low blood lactate levels, the research has shown that the body can be more effective at building higher mitochondria density in our muscles to the benefit of our performance. This could be beneficial for an endurance athlete trying to achieve higher endurance performance, or for a power and sprint athlete that may only do one aerobic session per week. Both types of athletes want to get the most benefit in terms of spending less time achieving a more significant benefit.

3. Improved Body Composition

Losing weight for most athletes is not good if you are losing muscle mass, or reducing your power to weight ratio. However, if you are reducing your body fat and increasing your power to weight ratio, then you can enjoy health benefits and sporting performance benefits.

Research has shown that training in a fasted state, at zone-2 intensity with low blood lactate, is a good way of getting into our maximum fat-burning zone (Fatmax). At this intensity this training produces less fatigue, so we can do more of this type of training, hence remain in this Fatmax zone for longer to the benefit of our body composition. There is a huge difference in where this maximum fat burning zone is for different people, and every athlete needs to know where their own Fatmax zone is in order to train to improve it, or to take advantage of it.


So to sum up, there are definitely benefits from fasted morning exercise. The three main ones are improved fat burning, building new mitochondria, and improved body composition.

Try training after drinking a coffee and going straight out on the road if you cycle or run - you will find it very time efficient.

However, it is IMPERATIVE to stay at your correct heart rate for zone-2, which will be personal to you, with low blood lactate levels. Blood Lactate Testing can certainly help you hit that Fatmax zone, see how I do that with my coached athletes here.

If you come back from the session super hungry and feel you want to eat the entire contents of the fridge, that is a sign that you went too hard. Alternately it could be a sign you have a Metabolic syndrome condition that is not good for your endurance performance or your long-term health. The good news is that this can be reversed for the benefit of performance and also long-term health.

Research Study

Steve carried out an online questionnaire survey titled "Nutritional Behaviours and Fuelling Strategies of Cyclists".

It was part of Steve's MSc Sports Nutrition research study to determine how cyclists fuel themselves before and during cycle training sessions. Also, if they undertake fasted cycling, but also high carbohydrate usage for training purposes.

The survey is closed now but Steve offered free resources on these subjects and they are still available, to obtain this free content, click on this survey link.

Other References

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5 comentários

Sandro Siqueira
Sandro Siqueira
21 de mar. de 2022

Can use caffeine capsules to do this fasted training in zone 2?

Steve Cronshaw
Steve Cronshaw
05 de abr. de 2022
Respondendo a

One proposed benefit of caffeine on exercise metabolism (beyond its widely accepted beneficial effects on the CNS) is that of increasing lipolysis (fat burning) and subsequent increased free fatty acid availability, which decreases the reliance on glycogen utilization during cycling to exhaustion at approximately 80% maximal oxygen uptake (VO2max). This is of significant importance when considering the benefits for fueling but also fatigue tolerance. While the source of fatigue is difficult to isolate for scientists, there is general agreement that a portion of it is attributed to muscle glycogen stores. This is beyond the benefits of caffeine itself on fatigue tolerance, which is significant.


Jeroen Nugteren
Jeroen Nugteren
08 de jan. de 2022

How ling is this fasted ride that is suggested here? 2, 3, 4 hours?

Steve Cronshaw
Steve Cronshaw
08 de jan. de 2022
Respondendo a

My suggestion is to start gradually with 1-hour and then build up slowly. It depends on how metabolically flexible you are for your body to burn different fuels carbohydrates or fats. If you have built up insulin resistance due to an intolerance to carbohydrates then you will find it more difficult to perform fat burning exercise. In the winter it is harder to do morning fasted rides as the body will consume more glycogen just to keep warm. Most people find it easier to do fasted rides in the summer.

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