Recently, I was asked a question about what the body uses for energy in an early morning workout, before breakfast, fat or muscle protein. Oddly enough, I still had my old Anatomy & Phsyiology book from undergrad and I felt that instead of answering by reasoning all of my knowledge, I should refer back to that book to find the correct answer.
The scenario: It’s 4:00, 5:00 , 6:00am, you just woke up and you are going to exercise on an empty stomach, having had your last meal the night before, we’ll say 9 hours ago. What is your body going to use for energy in this fasting state to power those muscles and get your routine done?
It’s the body’s job to maintain an constant level of blood glucose (sugar) because your nervous system can only run off glucose and ketone bodies for energy. When you eat, the majority of the glucose comes from your GI tract as the food is digested. But in a fasting state, where you haven’t eaten in over 4 hours, the body has to get its energy from storage. That can be fat tissue, within the muscles, or the liver. Your muscles prefer to use glucose as well, but since the nervous system needs it, that energy has to come from something else.
So what does your body use in this fasting state? The answer is Fat AND Muscle protein. The first reaction that skeletal muscle has is breaking down some of the proteins into amino acids that go into the blood to be broken down by the liver into usable energy. While that is happening, the muscles use fatty acids from adipose tissue (fat stores) first. The last source used is the muscle glyogen stores, which is more stored glucose.
Ok, so now you know what is breaking down, and what is fueling your body. So what? What does this mean for weight loss and body composition?
If you are solely looking to lose weight and drop your body fat percentage, this is a decent way to deplete the fat storage, thereby shrinking the size of the fat cells. And because you have exercised before eating, you body will continue to use these areas for energy until your GI tract is digesting food again, then it will reload those storage places in the muscles and liver before the adipose tissue.
If you are looking to gain size/muscle mass this is not the way to do it. By breaking down muscle protein, you in turn break the entire muscle down. It has to be rebuilt before it can grow. Those that want growth don’t want breakdown, they want breakage, where the muscle has to be repaired in order for hypertrophy to happen. And when you have adequate amount of energy in your blood where you don’t have to break the muscle down, size comes on more quickly.
Be sure to think about what your goals are before you exercise before eating. Make certain that you aren’t hindering your progress instead of enhancing it.