Table of contents
Fasted training – what is it, exactly?
As the name suggests, fasted training means exercising without food intake, i.e., on an empty stomach. Fasted training is a form of so-called fat metabolism training, practiced both by endurance athletes and by people with sporting and/or health-related interests. The aim is to have a positive effect, particularly on fat metabolism. However, training in a fasted state also triggers further metabolic adaptations, which will be examined in more detail in this blog article. At the end, you will also find a section that looks more closely at how the body generates energy during physical activity.
Positive metabolic changes through fasted training
In this section, we would like to discuss which positive metabolic changes may occur after training on an empty stomach. Particularly in recent years, many studies have examined this topic in depth, focusing on metabolic and muscle biochemistry parameters in connection with insulin sensitivity and glycaemic control. The latter are closely associated with conditions such as type 2 diabetes mellitus or insulin resistance. Some studies have shown that exercise training in a fasted state leads to improved glucose tolerance and insulin sensitivity.
In patients with type 2 diabetes mellitus or insulin resistance, an increase in intramuscular fat (fat stored in the muscle) is often observed. This fat is stored in the form of intramyocellular triacylglycerols [IMTG]. Fasted training can help transport it away more quickly and oxidise it more effectively (convert it into energy). This appears to lead to better protection against insulin resistance. Furthermore, another study found that the reduction in fat mass triggered by fasted training can contribute to improved glycemic control. A review article indicates that fasted training is associated with lower blood insulin, increased concentrations of free fatty acids in the blood, stable blood glucose concentrations (at least in the first 60-90 minutes), improved IMTG oxidation, and increased fat breakdown while preserving carbohydrate reserves. Long-term training in a fasted state can therefore improve insulin sensitivity and muscle fat oxidation. However, these preliminary results still need to be confirmed in further studies. The metabolic changes mentioned above resulting from fasted training can thus help boost one’s metabolism and prevent certain metabolic disorders, such as type 2 diabetes mellitus or insulin resistance. If you are affected by one of these conditions and would like to try fasted training, please speak with your treating physician beforehand to rule out hypoglycemia during training. How muscle fat oxidation works in detail and what influence fasted training has on it will be explained in a later section of this article. Another good way to positively influence your metabolism is intermittent fasting. How it works and what you need to consider can be found in this blog article: /intermittierendes-fasten/
Guide to fasted training
Intermittent fasting is a good introduction to fasted training, for example by scheduling your fasting period so that you skip breakfast and do a short workout instead. At the beginning, endurance sports such as hiking, jogging, or cycling are best. After a few weeks, once you are a bit more experienced, you can also add low-intensity strength training sessions.
It is very important that you stay below the so-called “anaerobic threshold” during training so that fat can be converted into energy in the form of ATP (the body’s universal energy carrier). This metabolic process requires oxygen, i.e., it must take place aerobically. In practice, this means you should remain in low to moderate intensity ranges, where you are challenged and sweat a little, but do not become too short of breath. Otherwise, the body switches to a less favourable anaerobic pathway of ATP production, which produces harmful lactate.
In addition, it is very important that you fully recover between individual training sessions. Ideally, plan your week so that you exercise three times, for at least 30 minutes each time—overall, you should be physically active for at least 150 minutes per week. You should also not train in a fasted state for longer than 60 minutes.
Nutrition during fasted training
This section focuses on what you should pay attention to in your diet. To activate the positive effects of fasted training, it is, first and foremost, important to actually be fasted before training. This means no milk in your coffee or tea in the morning. However, calorie-free drinks such as water and unsweetened teas are allowed.
There are several things to consider, especially when choosing dietary fats: high-quality oils should be preferred, particularly olive oil, as it contains a high proportion of monounsaturated fatty acids. Polyunsaturated oils such as flaxseed oil can also be used; however, do not heat them, store them in the refrigerator, and protect them from light. Other cooking oils, such as sunflower oil, are best avoided, as they undergo significantly more processing steps during refining. As a result, undesirable substances can enter the oil through numerous purification steps and valuable ingredients are lost (apart from the fact that sunflower oil has a high omega-6 content, which promotes inflammation).
Also essential for the body are the so-called omega-3 fatty acids, which are found in particularly high amounts in fatty cold-water fish (mackerel, salmon, herring).
If you do not like fish or do not wish to eat it, you can also use supplements made from marine algae to meet your daily needs.
Exercise and brain health
In addition to the positive effects that exercise can have on metabolic processes in our body, physical activity can also have a beneficial impact on our mental health. New research has shown that physical activity can also influence brain health, thereby improving resilience to dementia, depression, and stress.
This works as follows:
The brain receives indirect information—via adipose tissue and the liver—about how much we move. Robust research over the past two decades has shown that skeletal muscle also has secretory functions, meaning it is able to release certain hormone-like messenger substances (myokines). These myokines help ensure healthy brain function. There is new evidence that these messenger substances (including cathepsin B) are able to cross the blood–brain barrier, thereby promoting memory and our ability to learn.
Furthermore, research findings suggest that another myokine (myokine IL-6), which is also released through exercise, could help reduce our appetite. This implies that regular physical activity, for example through fasted training, could make an important contribution to regulating hunger and satiety.
Another interesting aspect of regular exercise is that it increases muscle expression of certain enzymes (kynurenine aminotransferases), thereby converting a neurotoxic amino acid (kynurenine) into an amino acid that protects the brain. Kynurenine is released in increased amounts during chronic stress and associated depressive symptoms. Exercise can therefore help reduce levels of this neurotoxin and alleviate depression-like symptoms.
Fasted training and sport
In the world of sport, this form of (endurance) training is about maximising energy supply from fatty acids in order to spare the body’s carbohydrate stores in the form of glycogen in muscles and liver. In addition, the amount of fat metabolised per unit of time (fat flux rate) during endurance exercise, as well as the fat oxidation rate, is intended to increase. To understand how this happens, we would like to explain how the body produces energy.
How does energy supply in the body actually work?
The body has several pathways for generating energy. In each case, adenosine triphosphate (ATP) is produced, which is the body’s primary energy carrier. However, the organism does not have unlimited amounts of ATP available; it must constantly produce new ATP. This occurs through the breakdown of our main dietary components (carbohydrates, fats, and proteins) via various metabolic pathways.
During prolonged exertion, the body’s fat stores (excluding structural fat around the heart, kidneys, joints, etc.) represent the most important and largest energy source, as 100–200 times more energy can be stored in adipose tissue than in carbohydrate stores. At the start of exertion, the body’s own glycogen stores (= carbohydrate stores) in blood, muscles, and liver are initially tapped to generate ATP. However, this only works for a certain time; with sustained exertion, the body’s glycogen stores become depleted and the body switches to generating energy from fats. This process can be supported by fasting before exercise, because fewer carbohydrates are available to the body and it uses fat as the primary fuel.
The most important site of fat storage in the human body is white adipose tissue, where fat is available for energy production in the form of triglycerides in adipocytes (fat-storing cells). Especially during fasted training, the body draws on this energy source.
A high-quality study from 2011 showed that consistent fasted training over 6 weeks improves energy supply from fats (fat oxidation) and increases the oxidative capacity of the muscles. This benefits not only athletes, but all of us, and can improve our attention and concentration. In addition, training in a fasted state can prevent a drop in blood glucose concentration. At the same time, the body’s ability to break down carbohydrates remains in a healthy balance, so that the optimal capacity for ATP production via carbohydrate breakdown is maintained. This appears to be related to increased breakdown of intramyocellular triacylglycerols [IMTG], as this supports the resynthesis of ATP. In this way, the sparing of carbohydrate stores during fasted training can be explained.
Thus, in specific moments of exertion, e.g., for final sprints or short, high intensities, muscle contraction in white muscle fibres can be ensured by carbohydrates.
With regularly practised fasted training, positive metabolic effects in energy production therefore occur. These include increased release of free fatty acids from adipocytes into muscle cells and a higher fat oxidation rate while preserving carbohydrate stores. More energy is then available in the muscle cells, which can increase endurance performance in the long term. This means better training results can be achieved at the same workload.
Another interesting aspect of fasted training is the improvement of carbohydrate metabolism. To enable the body to know how much energy is available, it uses a specific enzyme: AMP-activated protein kinase (AMPK). AMPK promotes resilience to oxidative stress and has life-extending effects. During fasting and subsequent fasted training, fewer carbohydrates are available to the body for ATP production. This energy deficit is registered by AMPK. Furthermore, this enzyme causes more ATP to be produced from the remaining carbohydrates. In other words, carbohydrate metabolism is optimised.
However, this positive effect only occurs with long-term practice of fasted training, because initially more mitochondria (the cell’s powerhouses) and new transporters must be formed. A review article from 2018 showed that only fasted training stimulates metabolic adaptations in skeletal muscle, and that food intake before training cancels out these effects.
Fasted training in elite sport
Of course, fasted training is also suitable for (elite) sport. To achieve better training results, training on an empty stomach is recommended because it leads to a higher fat oxidation rate while preserving carbohydrate stores. This can increase endurance performance in the long term and achieve better lap times at the same workload (e.g., in a marathon).
However, different requirements apply to performance and elite athletes, which we would like to explain here:
Unlike recreational health athletes, attention should be paid to a higher protein intake (approx. 30% of total daily energy) while reducing carbohydrate intake (approx. 50% of daily energy) and fat intake (approx. 20% of daily energy). To meet this increased protein requirement, sports nutrition products can be used.
Another difference compared to recreational health athletes is training frequency. Training should take place at least 6 times per week (a total of 360 minutes), and individual training sessions should be increased to at least 60 minutes. Training intensity can also be increased, with training more in the moderate to high intensity range.
In addition, (elite) athletes do not need to fully recover before moving into the next load phase. Incomplete breaks between training sessions are sufficient.
Conclusion
At this point, we would like to summarise the positive effects of fasted training once again in a clear way:
- Improvement of insulin resistance and glycaemic control
- improved resilience to dementia, depression, and stress
- positive metabolic effects in energy production
- increased release of free fatty acids from adipocytes into muscle cells
- higher fat oxidation rate while preserving carbohydrate stores – optimisation of carbohydrate metabolism
- better training results can be achieved at the same workload
- anti-ageing and life-extending effects
Try it and experience the positive effects of fasted movement/training on your body and mind. You can start with a short duration of activity and gradually work your way up. Fasted movement/training is particularly effective in combination with intermittent fasting, i.e., not eating anything for 13 to 16 hours at a time.
