Missing planned workouts happens to the best of us. In addition to the tremendous guilt deep inside your conscience, you notice that certain areas of our body that were once muscular are now ill defined. Well, the most obvious answer is that your hard earned muscle has now transformed into fat. However, this common exercise myth is far from the truth.
From the Plate to Body Fat
Body fat, or adipose tissue, is the way your body stores energy for an extended period of time. Every bite of food, or beverage that you drink, contains energy in the form of calories. This energy is necessary for you to perform your daily activities. However, when you take in too many calories, your body must store this additional energy in adipocytes, or fat cells. If you continue to consume large amounts of high-caloric food, then your fat cells will become larger and increase the amount of fatty tissue in your body.
A recent article (Nature 2008, 453(7196): 783-787) states that the number of fat cells in adulthood stays constant, even after weight loss, indicating that the number of fat cells is determined during childhood and adolescence. There are two points to take from this: 1) control the weight of your children now to prevent their risk of adult obesity, and 2) only the volume of fat in fat cells can change. Not the number of fat cells.
From Fat to Energy
One gram of fat equals nine calories of energy. Therefore, one pound of fat provides 3,500 calories. When your body demands energy through daily activities or physical exercise, many chemical reactions take place to transfer energy from a storage molecule (fat) to a molecule that can that muscles can use for energy (adenosine triphosphate, ATP). ATP is the energy molecule that fuels the body and helps your muscles contract. Therefore, fat does not turn into muscle, but acts as a fuel storage facility that can provide fuel, in the form of ATP, to muscles when they need it. As you increase your amount of exercise, your fuel stored as fat will decrease. At the same time, exercise increases muscle mass by causing existing muscle fibers to become larger and replicate.
Can Muscle Turn Into Fat?
Spending the day catching up on your digitally recorded shows can have a negative effect on muscle mass, but does not cause muscle to be turned into fat. Researchers at the University of Texas Medical Branch state that prolonged inactivity and stress cause both a decrease in muscle building and an increase in the breakdown of muscle fibers into protein (J Clin Endocrinol Metab 2006, 91(12): 4836-41). This protein is either used as energy in another part of the body, or excreted in urine. Therefore, the protein content of muscle is decreased during inactivity, but is not turned into fat.