According to Martin and Coe (1997), ‘carbohydrate is less efficient form of stored energy than fat’. They based this conclusion upon an observation that fats or triglycerides are 88% carbon and hydrogen and only 12% oxygen. Glycogen, on the other hand is 47% carbon and hydrogen, and 53% oxygen. When the body is in need of energy, glycogen becomes more accessible than fat because it has more oxygen which is needed by the cells (Martin and Coe 1997). Porth (2005) explains that while glucose produces 4 kcal per gram, a triglyceride or fat produces 9 kcal per gram.
Porth (2005) further claimed that one gram of water-free triglyceride is six times greater than one gram of hydrated glycogen. When fatty acids entered the cells due to increased metabolism, they engaged into what is known as oxidative phosphorylazation (Houston, 2006). Figure 1. 2. Summary of glucose and fatty acids interrelationship during the advent of metabolism. Source: Martin and Coe (1997) page 66 Glucose is the simple form of glycogen while fatty acid is the simple form of triglycerides.
Martin and Coe (1997), provide this basic illustration to explain the process that glucose and fatty acids undergo during metabolism. Both fatty acids and glucose enters either the skeletal muscle tissue or the adipose tissue during metabolism. When the skeletal muscle tissues or other cells do not consume glucose, it will enter the adipose cells to be eventually converted into triglyceride. On the other hand, during intense metabolism, certain hormones breakdown triglycerides into fatty acids and send them to the cells. In the skeletal muscle cells, they are usually converted to energy.
In the adipose cells, they are stored as back up for possible release and transport into the muscle cells. Figure 1. 3. Energy Substrates available for Metabolism Source: Martin and Coe (1997) page 65 To further clarify the extent to which glycerol and triglycerides acts as fuel reserves. Martin and Coe (1997), shows (Figure 1. 3) the energy substrates that are available for metabolism in tissues and in circulating fuels. It shows that there are more fat stored in tissues than glycogen. Furthermore, it also illustrates that there is actually a very small amount of glycogen in muscle and liver.
Nonetheless, it is noticeable that the amount of glucose as circulating fuels is greater than fatty acids and triglycerides. Nonetheless, despite the fact that there is only . 003 kg of triglycerides as circulating fuels it already accounts to 30 kcal. While extracellular fluid glucose, has . 020 kg in circulating fuels, it can only produce 80 kcal. This shows that triglycerides are more efficient in storing energy. It can also be associated with the statement made by Porth (above) that indeed fats can produce more energy than glycogen. Figure 1. 4
Source: The Obesity Society. www. obesityonline. org The Obesity Society (2008), further elaborates that triglycerides in the adipocytes or in the adipose tissues has about 0. 4 to 0. 6 µg fats. According to their report (Figure 1. 4), the adipose tissue stores the greatest amount of energy in the body in the form of triglycerides. The Obesity Society (2008) also mentioned that triglycerides are actually five times better as fuel than glycogen because it is more compact. This statement is similar with the ones held by Martin and Coe (1997) and Porth (2005). Conclusion
Glucose is the primary energy used by the body that is generated through food intake via intestinal absorption of glucose. Nevertheless, the body only need a specific amount of glucose at a certain time. This prompted the synthesis of glucose into glycogen. Triglycerides enter the body as fats or are produced as triglycerides from unused glycogen. Different hormones and enzymes affect the degradation and synthesis of glycogen and triglycerides. Fasting and muscle contraction accelerates the degradation or catabolic process of glycogen and triglycerides since blood glucose levels drops.
On the other hand, food intake and resting facilitates glycogen and triglycerides synthesis and storage. References: Champe, PC, Harvey, RA and Ferrier, DR. 2007. Biochemistry. Fourth Edition. Lippincott Williams & Wilkins. Houston, ME. 2006. Biochemistry Primer for Exercise Science: A Better Basic Understanding of Biochemistry. Human Kinetics Publishers, Inc. Martin, DE and Coe, PE. 1997. Better Training for Distance Runners. Human Kinetics Publishers, Inc. IL, USA. Porth, C. 2005. Pathophysiology: Concepts of Altered Health States. Seventh Edition.
Lippincott Williams & Wilkins. Sherwood, L. 2005. Fundamentals of Physiology: A Human Perspective. Thomson Brooks/Cole. Smith, C, Marks, A and Lieberman, MA. 2004. Marks’ Basic Medical Biochemistry: A clinical approach. Second Edition. Lippincott Williams ; Wilkins. Stryer, L, Berg, JM and Tymoczo, TL. 2006. Biochemistry: International Edition. W. H. Freeman ; Co Ltd. The Obesity Society. 2008. Body Energy Stores Of Lean 70 Kg Man. Retrieved on Novmber 24, 2008 from http://www. obesityonline. org/slides/slide01. cfm? q=liver+glycogen;pg=1