Long Cardio Tips For Empty Stomachs

Performing cardio or aerobic activity on an empty stomach is a debated topic in regard to weight and fat loss. The idea is that without calories from food, your body will use other fuels, like fat, during your workout. However, working out without food for fuel can possibly lead your body to burn muscle instead. Taking proper precautions can keep your body from breaking down muscle and help it use the right energy sources.

Muscle Glycogen

When you eat, your body transforms food into energy. Your body stores some of this energy as glycogen in both your muscles and your liver. When you reduce your intake of calories, your body uses glycogen for fuel. Glycogen retains water, so when you use glycogen, you also release water. According to the Mayo Clinic, you release about 4 g of water for every gram of glycogen, which can lead to substantial weight loss that is mostly water. If you are working out on an empty stomach, you can burn glycogen, which will reduce your water weight.

Cortisol and Cardio

Cortisol, a hormone involved in your body's stress response, is also involved in exercise of any kind and can determine what type of energy is used as fuel. Your body releases cortisol whenever you exercise. More is released when you weight train than do aerobic exercise. Cortisol also increases the use of alternate fuels for muscle, such as fatty acids and amino acids. It can also break down muscle to use for energy. All of these cortisol functions increase during times of low body carbohydrate nutrition, when your blood sugar is lower.

Benefits of Food

Although performing long cardio or endurance exercise can burn glycogen stores and reduce water weight, cortisol levels can potentially cause you to burn muscle stores if blood sugar is low. Eating or drinking a small amount of carbohydrate, like juice or a piece of toast, can prevent that from occurring. A small amount of food can also improve your performance level, increasing your "after burn," or ability to burn calories after your workout, states Ken Wall, fitness director at Odyssey Fitness Center in Wilkes-Barre, Pennsylvania.

Shorter Workouts

When aerobic activity is performed in short intervals, less than 45 minutes, the exercise-induced cortisol release will most likely not result in muscle breakdown. If you are performing cardio on an empty stomach, limiting yourself to 45 minutes may be beneficial. Your body will also simultaneously release substances like growth hormone and testosterone that can counteract the effects of cortisol, preventing muscle breakdown.