The processes of fat loss and muscle gain goes hand-in-hand because having more muscle mass in your body will increase your fat-burning potential. However, many people who wish to lose weight do not understand this basic concept, and many diets and weight-loss centers do not emphasize that fact to their consumers, which leads their customers to regain the weight that they had lost. Understanding the basics of how fat is metabolized will help you make better decisions in your exercise and dietary habits.
Fat Metabolism
During exercise, fat stored in adipose and muscle tissues is broken down into fatty acids and glycerol, which are the basic components of fat (triglycerides). They are then released into the bloodstream and are brought to the muscle cells, where the fatty acids are transported into the cell's mitochondria to make adenosine triphosphate, which is a high-energy compound that all cells use to make energy.
In the mitochondria, which is the energy factory of all cells, fats are broken down into their basic carbon and hydrogen components. Oxygen is then combined with the carbon atoms to form carbon dioxide and hydrogen atoms to form water. Carbon dioxide is released from your lungs and water is sweated out through your skin.
Muscle Growth
Muscles increase in size by increasing the number of contractile proteins, actin and myosin, to increase size and strength. You also increase how many motor units are recruited for muscle activation, which are neurons inside nerve fibers that connect from the spinal cord and are dispersed throughout the muscle fibers. When you do strength training or anaerobic training (without oxygen), you increase the number of motor units you recruit and the amount of actin and myosin created. There is a limit, however, on how much size you can gain, due to the genetic make-up of your body and the number of contractile proteins available.
Aerobic Respiration
Inside the mitochondria, fatty acids are metabolized using aerobic metabolism, in which oxygen and acetyl-CoA (a byproduct of glucose and fat metabolism) are combined and used to start the citric acid cycle to generate more adenosine triphosphates (ATP), which are high-energy molecules that every cell in your body uses.
First, fatty acids turn into acetyl-CoA via beta-oxidation, which involves splitting off two carbon acyl fragments from the fatty acid chain. During the degrading process, hydrogen is released from the chain, which is combined with oxygen to form water. Once acetyl-CoA is formed, it combines with oxaloacetate to trigger a chain reaction of chemical reactions to form ATP, carbon dioxide and hydrogen exchanges in the citric acid cycle, which contains eleven irreversible steps. Each step is dependent on the previous step to occur. Otherwise, the process would slow down, which causes a decrease of energy production. The net amount of energy generated from this process from three molecules of fat is 441 ATP.
EPOC
High-intensity exercise (mainly anaerobics) uses carbohydrates as a primary fuel source. The winded or burning sensation that you get, also known as excess post-oxygen consumption (EPOC), uses fat as a major fuel source. This is a state in which you are increasing your oxygen intake after strenuous exercise to balance the body's lack-of-oxygen state. Your body undergoes a recovery state in which it is getting back to the resting state--balancing hormones, replenishing energy in muscles and repairing cellular damage. All of these activities require energy, and that source comes mainly from fat. The more muscles you have, the higher your EPOC rate.
Misconceptions
Many people who want to lose body fat in certain parts of their bodies---known as spot reduction---perform repetitive exercises that target those specific areas, such as sit-ups for the abs, tricep exercises for underarm fat, and leg exercises for thigh fat. However, your body does not burn body fat in specific areas. Instead, it involves the entire body. In fact, doing repetitive exercises with resistance can cause the muscles to increase in size, resulting in bigger waistline, arms and thighs.
Another misconception is that you will gain more muscle if you eat more protein. However, your body can only synthesize and process a limited amount of protein to repair and perform other vital functions. Excess unused protein is converted to fat for storage.
References
- "Perspectives in Nutrition"; Gordon Wardlaw and Margaret Kessel; 2002
- "Winning at Losing: Secrets of Long-Term Weight Loss"; Len Kravitz; 2007
- "Hierarchy of Fat Loss"; Alwyn Cosgrove; 2007
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