What are the benefits of running on an empty stomach?
Whether you are looking to lose weight by running or simply to train your metabolism so that your fuel absorption is better during exercise, fasted running can be a way to train your body to draw on its fat stores. People who practice fasted running generally exercise in the morning before breakfast, but it is also possible to do so during the day after four to five hours or more without eating.
Although the idea is not new, it has recently gained renewed traction in the world of endurance sports. Indeed, it seems to align with the ultimate goal of many runners: losing weight and improving their performance. Nevertheless, the effectiveness of this technique depends on your training goals and the methods you use: short, intense, frequent runs or longer, slower runs?
The metabolism adapts
First of all, fasted cardio and fat consumption should be considered within the longer-term context of your weekly calorie intake: it is not only the calories burned during exercise that matter. An excellent example is high-intensity interval training, during which a runner may perform 10 high-intensity efforts over a short period, 20 seconds for example, with only 30 to 60 seconds of rest between repetitions. The total number of calories burned during this kind of session is low, but the long-term metabolic benefits are real.
Fasted running: a delicate balance
Whether or not to eat before a workout depends specifically on the type of training you are doing. Eating before exercise will not cancel out all the fat burned by your metabolism during the run, and not eating will not lead to massive fat consumption as some would like to believe. It is about training your body to be able to cope with all kinds of situations.
For a low-intensity session such as a one-hour run, eating less beforehand and compensating with more substantial recovery afterward stimulates the enzymes activated during fat consumption. However, eating before exercise is not entirely without benefits either. In fact, starting with a full or at least satisfied stomach allows you to handle a longer session. Ultimately, what matters most is the runner’s eating habits throughout the week, as well as the frequency of the sessions.
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Burning carbohydrates or fat?
Most runners consume carbohydrates before a race so they do not run out of energy: a plate of pasta the night before a marathon, for example. When practicing fasted cardio, the emphasis is placed on the body’s ability to use fat. When fasting, during the less demanding parts of the run, the runner therefore uses their fat stores and preserves their carbohydrate reserves for the more challenging sections.
A well-trained runner is able to burn fat just as efficiently as carbohydrates. This gives them a greater energy reserve at their disposal. The two sources are not interchangeable. During marathons and shorter distances, carbohydrates are the primary energy source used by your body: it is therefore important to train while adequately fueled. During longer races, such as ultratrails, the body’s ability to burn fat has a significant impact.
There is also a separate category: those who combine long and intense effort, such as runners capable of completing a marathon in under three hours. They train to use only their carbohydrate reserves during exercise because fat does not generate enough energy to meet their high demands. Burning fat consumes oxygen, which is generally the main limiting factor when you are capable of running a marathon in under 2h30.
If you decide to get started and train your body to exercise while fasted, here are a few final tips to conclude:
- Begin your fasted training gradually by increasing the duration little by little and keeping your pace fairly slow at first.
- Do not start a completely fasted session if it means finishing ravenous and feasting after exercise.
- After a fasted run, recovery is even more important.
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