Fasted cardio is an exercise practice that has gained popularity in recent years. “Fasted cardio means exercising after fasting at least for 12 hours. For example, waking up in the morning and exercising without eating anything,” says Dr Ashish Contractor, Director of dept of rehabilitation and sports medicine at Sir HN Reliance Foundation Hospital, Mumbai.
Fasted cardio is based on the idea that by exercising empty stomach, the body taps into its fat stores for energy more efficiently, leading to increased fat burning and weight loss. This approach – its potential benefits and drawbacks – has left the fitness world polarized.
Cardio involves continuous, rhythmic movements that engage large muscle groups and promote efficient circulation of blood and oxygen. Common cardio exercises include running, swimming, cycling, brisk walking, dancing, and aerobic workouts.
Proponents argue that fasted cardio can optimize fat oxidation, enhance insulin sensitivity, and boost overall metabolic health. Critics, on the other hand, say the benefits of fasted cardio may be overstated and that it could potentially lead to muscle loss or decreased exercise performance.
Effects of fasted cardio on your body
Fasted cardio has been suggested to improve insulin sensitivity, which is how effectively the body uses insulin to regulate blood sugar levels. A study published in The Journal of Physiology, found that early morning exercise in the fasted state is more potent than an identical amount of exercise in a fed state in improving whole-body glucose tolerance, as well as to induce beneficial adaptations in muscle cells that eventually may contribute to improved insulin sensitivity. Enhanced insulin sensitivity can be beneficial for overall metabolic health and may help with weight management.
The common belief is that exercising in a fasted state may enhance the body’s ability to utilize stored fat as a fuel source. When glycogen (stored carbohydrates) levels are depleted, the body may rely more on fat stores for energy, potentially leading to increased fat burning during the workout.
However, a study published in the Journal of the International Society of Sports Nutrition found that the body composition changes associated with aerobic exercise in conjunction with a hypocaloric (calorie deficit) diet are similar regardless of whether the individual has fasted prior to training or not.
Fatigue and fasted cardio
Working out on an empty stomach may leave you tired and could affect your endurance. Not having energy will reduce your exercise performance, intensity, and volume of the workout.
Is fasted cardio worth it?
“The difference between fasted cardio and waking up in the morning and having an apple, is not going to make a dramatic difference,” says Dr Contractor. “These are very nuanced strategies as a very specific training goal for somebody who is trying to achieve a high point, in terms of health and fitness.”
On top of this, fasted cardio has also been associated with the potential for muscle catabolism (breakdown) as the body may utilize muscle protein for energy when glycogen stores are low.
“For 99% of the population, the important thing is to go out in the morning and exercise. Even if you burn one more gram of fat in a fasted state, it is merely 2% of the whole fitness conversation.”
Takeaways
- Fasted cardio means performing cardiovascular exercise on an empty stomach, typically in the morning before consuming any food.
- Body composition changes associated with aerobic exercise in conjunction with a hypocaloric (calorie deficit) diet are similar, regardless of whether an individual is fasted prior to training.
- Early morning exercise in the fasted state is more potent than an identical amount of exercise in the fed state to improve whole-body glucose tolerance and may contribute to improved insulin sensitivity.
