Buzz
Having tried fasted morning cardio myself, I get the appeal. It feels like a noble effort: pushing through discomfort, challenging yourself, yet not overdoing it. You complete your run on an empty stomach, looking forward to a well-deserved breakfast. But does this sacrifice actually yield results?
Occasionally, studies emerge suggesting that fasted or morning exercise is a key to burning fat. A recent study that made headlines involved mice, showing increased fat-burning markers in those that ran on a treadmill during their “morning” compared to those that exercised in the “evening.” Interestingly, fasting didn’t impact the results—only the timing of the exercise mattered.
(Here’s an interesting tidbit about rodent studies on circadian rhythms: mice are nocturnal, so their “morning” is our evening. This reversal is crucial when interpreting how such findings might apply to humans.)
For many people, morning workouts and exercising on an empty stomach often coincide, making fasted morning cardio a widely recommended weight-loss strategy. But does it truly deliver better results? Personally, I prefer sleeping in these days and won’t return to early morning exercise routines just because of some metabolic changes observed in rodents. Let’s explore whether this and other so-called fat-burning exercises hold any real significance in the grand scheme of things.
The role of fat burning during exercise isn’t as crucial as you might believe
If weight loss is your goal, burning fat seems beneficial, right? However, burning fat during exercise doesn’t automatically translate to overall fat loss. Think of fat like a wallet: you can withdraw energy (spend it), but you might replenish it later in the day. What truly matters is your net energy balance over time—whether it’s daily, weekly, or monthly.
Similarly, the type of fuel you burn during exercise isn’t the deciding factor. Whether you’re burning fat through low-intensity fasted cardio or carbs during an evening HIIT session after a sports drink, your body will adjust accordingly. If you burn more calories than you consume, you’ll lose energy—ideally from fat. Conversely, eating more than you burn leads to the opposite outcome.
Scientific research examining whether fasted cardio leads to overall fat loss often finds no significant difference between exercising with or without food. For instance, this study found no notable distinction between groups who ran in a fasted state and those who consumed a shake before or after their morning workout.
Taking a broader perspective, this review concludes that there’s “no definitive evidence proving fasted cardio is superior to fed cardio for improving body composition.” It also warns that excessive fasted cardio—such as sessions lasting over an hour—might lead the body to break down muscle for energy. So, if you overcommit to fasted cardio, the approach could end up being counterproductive.
Fasted morning cardio comes with its drawbacks
If you exercise early and occasionally skip eating beforehand, it’s likely fine—your progress won’t be ruined. However, if you can eat first, you’ll probably perform better during your workout.
Low-intensity cardio (zone 2 on a five-zone scale) primarily relies on fat for energy, so you might not feel much difference whether you eat before or not. Even if fasted morning jogs feel challenging initially, your body can adapt over time. Many people enjoy running before breakfast, and while it may not be ideal, it’s perfectly acceptable.
However, for higher-intensity workouts, you’ll likely feel the absence of carbs. Having glycogen in your muscles or sufficient blood sugar can reduce fatigue and enhance performance. If eating before exercise improves your workout quality, why wouldn’t you fuel up properly?
