Carbohydrate Metabolism
Carbohydrate Metabolism is an important role in producing ATP, along with the other macronutreints (fats and proteins). Carbohydrate metabolism takes place during the three main Energy Transfer Process which are designed to break down this macronutrient’s (along with fats and proteins) chemical bonds to form ATP. Carbohydrates are very important for good nutrition in your diet. They are our bodies fastest macronutrient source of energy, but they are stored in our body in very limited quantities. A typical 150 pound person may have about 1.1 pounds of stored glucose in their body which is only about 2,000 calories. Indeed, during lean times the carbohydrates will not last very long and our body would rely on the micronutrient that is most abundant; fat. So, to maintain our carbohydrate stores, we must generate them from our dietary intake. This does not mean that you have to have a diet that is high in carbohydrates to maintain your body’s glucose levels. Your body can produce the extra glucose it needs from other sources such as proteins and other non-carbohydrate compounds. In addition to the proteins and other non-carbohydrate compounds creating extra glucose, the body has plenty of fat to use as fuel for energy transfer.
For carbohydrate metabolism, there are five major pathways that this macronutrient is metabolized in its goal of creating ATP. They are: 1) The Glycogenesis Pathway, 2) The Glycogenolysis Pathway, 3) The Glycolysis Pathway, 4) The Krebs Cycle and Electron Transfer Pathway, and 5) The Gluconeogenesis Pathway.
As a side note, “glyco” = sugar; and words ending in “lysis” mean the breaking down or splitting apart, and words ending in “genesis” mean the creation or new. Now at a glance at each of these pathways you can tell which ones are breaking down to sugars to form ATP, and which ones are building them up to create ATP.
1) Carbohydrate Metabolism -The Glycogenesis Pathway
Glycogenesis simple put is the building of new glycogen. Our dietary carbohydrates are stored in our body as glycogen. These glycogen molecules are made up of glucose molecules that are chemically bound together and store in the tissues of the muscles and in the liver. For the glucose to be added to glycogen it must be transported to the liver with carrier proteins where it is transformed into glucose 6-phosphate. Once this process takes place, glucose molecules can attach themselves to existing chains glucose molecules to form glycogen.
2) Carbohydrate Metabolism – The Glycogenolysis Pathway
Now that our body has created long glycogen molecules through the glycogenesis pathway they are ready for use in high energy situations. It is through The Glycogenolysis Pathway that they will be split apart for energy use. During high energy situations the body needs glucose for energy transfer and will send a signal to the glycogen phosphate enzyme to split the glycogen molecule apart to use it as glucose. Once broken down by the phosphate the glucose “picks up” the phosphate. This new compound can either enter the muscle and through the glycolytic energy pathway to generate ATP, or be released directly into the bloodstream.
During times of “feast” where energy demands are low, the body goes into storage mode and will get the glucose it needs from insulin release. But during times of high energy such as strenuous exercise, both the Glycogenesis Pathway and the Glycogenolysis Pathway are the main suppliers of glucose.
3) Carbohydrate Metabolism – The Glycolysis Pathway
The Glycolysis Pathway converts glucose into two molecules of pyruvate, and the energy that is released from this process forms ATP. This process takes place in the cytoplasm of virtually all of our cells. The glucose that is used in glycolysis can be derived from either blood glucose or stored glycogen. The end results is that 4 molecules of ATP are formed through the Glycolysis Pathway.
During anaerobic activities where the energy level is high, glycolysis runs fast to keep up with the demand for ATP. However, when energy demands are below the anaerobic threshold, the Krebs Cycle within the Oxidative Energy Pathway is capable of keeping up with the rate of glycolysis.
4) Carbohydrate Metabolism – The Krebs Cycle and Electron Transfer Pathway
The Krebs Cycle is an extremely complex process of not only breaking glucose (carbohydrates) down, but it also breaks down proteins and fats; with the goal of producing ATP. The side effect of this process is that it also produces carbon dioxide. In the Krebs Cycle, two carbon coenzymes are joined with carbon compounds and are transformed into energy. Good nutrition and proper vitamin intake play an important role in the Krebs Cycle. If certain components of coenzymes and vitamin deficiencies exists, then the process of energy transfer can be hampered.
When people decrease their carbohydrate intake or start on a low-carb diet, they may feel sluggish and have low energy. This is because they are not producing enough ATP through the Krebs Cycle to meet their energy demands, and the liver does not have enough stored glucose to offer the brain and red blood cells. This is important because the brain and red blood cells can not store their own glucose and must have it supplied to them. So what does the body do during this low level of carbohydrates? it slows down to match the reduced ATP availability.
This by no means is a call to action to start a high carbohydrate diet because your body has ways to compensate for the lower ATP levels. After about 14 days of being on a restricted carbohydrate diet, your fatty acid deposits will start to generate ketones in the liver and kidneys. These ketones becomes a vital source of energy during fasting.
5) Carbohydrate Metabolism – The Gluconeogenesis Pathway
The Gluconeogenesis Pathway is responsible for maintaining the blood glucose levels by generating glucose from non-carbohydrates such as lactate, glycerol, and amino acids.. This is vital since plasma levels of glucose are required to provide glucose for energy transfer in the brain. In the Gluconeogenesis Pathway these non-carbohydrates are transported to the liver where they are converted into pyruvate, which then can be converted into glucose.
