Laban Laban, Bawi Bawi! - Energy Substrates + Energy Systems

By Sophia Villaflor

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We need energy in our everyday lives, in order to move around and carry out different tasks. We also need it in order for our bodies to perform the different processes needed to keep us healthy and functioning well. Here, we find out where we get our energy and how our body uses it.

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We have 3 basic fuels, or energy substrates, that are broken down to release energy.

1. Carbohydrates

Our first energy substrate is carbohydrates. Carbohydrates are “the sugars, starches, and fibers found in fruit, grains, vegetables, and milk products,” (Szalay, 2021). They provide energy for the central nervous system and working muscles. Carbohydrates, in their basic form, are known as glucose. Also known as dextrose, glucose is part of a group of carbohydrates known as the monosaccharides, or simple sugars. This is the major free sugar that goes around the blood of higher animals like mammals. Glucose is also the source of energy in cell function, and can be found in foods like fruits and honey.

The rapid breakdown of carbohydrates is known as glycolysis, wherein glucose and glycogen are broken down to form ATP, or adenosine triphosphate. Glycolysis is used by all cells in the body for energy generation, and is the first step in cellular respiration. This process extracts energy from glucose by splitting it into pyruvates, which are three-carbon molecules. Once we reach the end of glycolysis, we now have two ATP, two NADH (nicotinamide adenine dinucleotide (NAD) + hydrogen (H)), and two pyruvate molecules. In cellular respiration, the pyruvate can be oxidized, or broken down, all the way to carbon dioxide. This makes a numerous amount of molecules of ATP.

2. Fat

Second, we have fat. While fat may have a negative connotation, we have to remember that we need it in order for our body to absorb vitamin A, vitamin D, and vitamin E. This is because these vitamins are fat-soluble, meaning that they need fat in order to be absorbed by the body. Fat is also a source of essential fatty acids, which the body cannot make these fatty acids by itself. This is why consuming foods with the right amount of fat is important. There are different types of fat, such as saturated fat, unsaturated fat, and trans fat. Saturated fat mostly comes from animals, such as meat and dairy products, but some can be obtained in plants, such as palm and coconut oil. Consuming too much of this fat might increase the “bad” cholesterol in your blood, thus also increasing the risk of heart disease and stroke. Unsaturated fat, on the other hand, helps lower your cholesterol level. This can be found in oils from plants and fish. Lastly, we have trans fat, which can be found in low levels in some foods, and also in vegetable oil. Because like saturated fats, this raises the cholesterol levels in the blood, it is recommended to have this fat in minimal amounts.

The process by which fats are broken down by our body is known as lipolysis. This can be done through enzymes and water, or through hydrolysis. Lipolysis occurs in our adipose tissue, which are the fatty tissues that cushion and line our bodies and organs. This process is important to the body because the glycerol produced by lipolysis is a source of carbon for the transformation of non-carbohydrate substrates such as lactate, amino acids, and glycerol into glucose in the liver.

3. Proteins

Our third energy substrate is proteins, which is found in virtually every part of our body. Protein makes up the enzymes that power our body’s chemical reactions and also the hemoglobin, which carries oxygen to the blood. Amino acids are what make up proteins, with 9 amino acids, known as the essential amino acids, needing to come from the food we eat. Examples of such foods include: meat, poultry, fish, and dairy. Nonetheless, we have to remember that it is the source of protein, not the amount of protein, which creates an impact on our health.

Protein is absorbed into our body through the process known as protein breakdown. Once protein from the food you have eaten reaches your stomach, hydrochloric acid and enzymes known as proteases break it down into amino acids and move into the small intestine. Here in the small intestine is also where your body will absorb the amino acids from the protein, which is done through the microvilli. Once your body has absorbed the amino acids, they are released into the bloodstream, which takes them to cells in different parts of your body in order to be able to repair tissue and build muscle.

Next, we have our energy systems, or how our body releases energy through our everyday movements

Glycolytic System

First, we have the Glycolytic system, which relies on the rapid breakdown of carbohydrates into glucose, the most basic form of carbohydrates. A variation of glucose, known as glycogen, is a stored form of glucose in the muscles and liver. In glycolysis, glucose and glycogen are broken down in order to form ATP. In this process, a substance called lactate is formed and hydrogen ions are released. It is believed that the build-up of hydrogen ions in the muscle can cause it to become more acidic, which contributes to fatigue and leaves a burning sensation. Glycolysis happens when movements at maximum effort are performed for 1 to 2 minutes, like running at full speed for 50 meters

ATP-PCR

Second, we have the ATP-PCR system. This process is based on short, sustained movements lasting about 5-15 seconds, like strength-power movements like jumping. This process can be done only with the ATP that is stored in the muscles. ATP-PCR may last ≈4 to 6 seconds with a compound known as creatine phosphate (PCr), and may last up to ≈10 seconds because PCr produces more ATP. This process produces energy quickly, but not over a long duration.

Oxidative System

Unlike the two energy systems before this, the oxidative system involves the use of oxygen. Here, the Krebs cycle and the electron transport chain are what produce ATP. Another thing that sets this system apart from the other two is that ATP is produced slowly, and for a long duration of time. This system is used for endurance activities for longer periods of time.

Knowing how we gain and use up energy can be helpful when choosing what food to eat and what diet to take up, which is why it's important to remember the different kinds of energy substrates and systems.

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Sources

• BD Editors. (2018, September 18). Lipolysis - Definition, Mechanism and Process | Biology Dictionary. Biology Dictionary. https://biologydictionary.net/lipolysis/

• Dix, M. (2021, March 31). How Is Protein Digested? Healthline; Healthline Media. https://www.healthline.com/health/protein-digestion#takeaway

• Edwards, M., & Mohiuddin, S. S. (2021, July 22). Biochemistry, Lipolysis. Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK560564/#:~:text=Lipolysis%20is%20the%20metabolic%20process,heat%2C%20energy%2C%20and%20insulation.

• Khan Academy. (2022). Khanacademy.org. https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/glycolysis/a/glycolysis

• Kumari, A. (2018). Glycolysis. Sweet Biochemistry, 1–5. https://doi.org/10.1016/b978-0-12-814453-4.00001-7

• Merriam-Webster Dictionary. (2020). Merriam-Webster.com. https://www.merriam-webster.com/dictionary/body-shaming

• NHS Choices. (2022). Fat: the facts - Eat well. https://www.nhs.uk/live-well/eat-well/different-fats-nutrition/ Protein. (2012, September 18). The Nutrition Source. https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/#:~:text=Animal%2Dbased%20foods%20(meat%2C,or%20more%20essential%20amino%20acid.

• Szalay, J. (2021, November 24). What are carbohydrates? Livescience.com; Live Science. https://www.livescience.com/51976-carbohydrates.html

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