For a long time, the claim has persisted that working out on an empty stomach is particularly good if you want to lose weight. But is there any truth to this assumption—is it true or nonsense? You probably won't find a definitive answer. Let's take a closer look at the benefits fasted training can offer and what potential drawbacks it might have.
What exactly is fasted training?
To understand what we're actually talking about here, we first need to clarify when a workout can be considered on an empty stomach. Fasted means you haven't eaten anything or consumed liquid calories for a certain period before your workout. For the vast majority of people, this means in the morning. You are in a fasted state when you haven't consumed any calories for 8 to 12 hours. This depends somewhat on what you ate last. A huge portion of pasta the night before probably takes longer to digest and burn than a serving of cooked vegetables with a piece of fish. Most people reach a fasted state in the morning after waking up. So we're talking about a workout right after getting up—without eating breakfast first.
Theory: Working out on an empty stomach boosts fat burning
At least, that was the prevailing opinion for a long time. But is that actually true? And does that automatically mean you'll lose weight? Let's take a closer look: Where does the body get the energy for physical exertion during a morning fasted workout? Over night, during your fasting phase, your body draws from its carbohydrate stores to maintain body functions. Yet glycogen from carbohydrate stores is precisely what your body prefers as quick energy during a workout session. Therefore, according to the theory, during a morning workout after the overnight fasting phase, the body must rely more on energy from fat stores. However, scientific studies on this topic offer no clear pro or contra arguments. Still, it seems that over time, your body gradually learns to use fat as an energy source faster and more efficiently. Which, in itself, is a good thing.
What are the benefits of working out on an empty stomach?
People who have been doing fasted morning workouts for a while appreciate several benefits:
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For many, it's simply more comfortable to work out on an empty stomach
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You can comfortably check off your workout session for the day right afterward
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Studies suggest that fasted training improves aerobic base endurance
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The body learns to make better use of its fat reserves as an energy source
Endurance athletes in particular who like to go for an early morning run before their first meal appreciate fasted training. In general, moderate endurance training early in the morning on an empty stomach is much better suited than physically demanding strength training.
When you should avoid fasted workouts
Although the body can apparently learn to optimize its fat metabolism through regular fasted training, this does not mean you automatically lose weight. Unfortunately—it would be nice if that were the case, as anyone wanting to lose weight would then only work out on an empty stomach in the morning. However, it still comes down to your total daily caloric balance to positively influence your weight loss success. So if you want to lose weight, the principle still applies: burn more calories per day than you consume! There are certainly valid arguments why fasted workouts might not be right for you. If you generally struggle with circulatory issues, working out on an empty stomach might cause dizziness. You can experience low blood sugar faster than others. In that case, it's better to avoid training on an empty stomach. Furthermore, it appears that the body cannot achieve top performance during workouts performed in a fasted state.
So what does science say about fasted training?
That's quite simple to answer: Currently, there is no definitive consensus on whether fasted training truly provides the fitness or weight loss benefits you hope for. There are, of course, various studies on the topic or specific aspects of it, but no unanimous scientific finding clearly speaks for or against fasted workouts. Therefore, the rule of thumb is: Just try it out for yourself. After an adjustment period, you might find it great and stick with it. But if you notice that you consistently feel unwell during or shortly after exercising, simply stick to a small, healthy breakfast snack before working out. There are still people who feel great working out on an empty stomach and others who can't handle it at all. Both are completely fine. The most important thing—especially if you want to lose weight—is combining calorie burning with a healthy diet to achieve an overall negative calorie balance for the day. And for that, your body doesn't care whether you work out on an empty stomach in the morning or not.
