Science for Everyone #1: How We Get Fuel from Food

It’s been a while since my Introduceyourself post and things have been pretty busy, but I finally found time to write my first Science post! Since our research focuses on how changes in diet affect survival times in brain cancer, I thought a good place to start for the first installment of the Science series would be to go over the process of digestion and how we get energy from our food. From here, we can move on to the ketogenic diet and how it impacts cancerous tumors.

How do we get our energy?

We eat other animals and/or plants!

Unlike plants, which are able to harness energy from sun’s light and convert it into a usable form through photosynthesis, humans need to eat other organisms and “steal” their energy, whether it be from plants directly or from other animals that in turn ate plants. This is what is meant when someone says food chain. Plants harness the sun’s energy to make fuel, small animals eat plants taking their energy, and bigger animals eat smaller animals all while the original energy from the sun is passed up the chain.

Breaking down food to produce energy

While the food we eat contains the energy we need, we are not able to access this energy until food is broken down into small molecules or digested. This process begins as soon as food enters your mouth. The breakdown process begins with chewing which smashes and tears our bites into smaller particles that are more easily digested. This process is helped along by enzymes contained in your saliva such as salivary amylase, which helps breaks down large strands of carbohydrates (glucose, sucrose, etc.) into individual molecules. After food is chewed and swallowed it reaches the stomach where it is bathed in hydrochloric acid. The pH of the stomach is around 2, which is a highly acidic environment. This acidity is needed to activate the enzymes in your stomach that further break down food into components such as amino acids, sugars (carbohydrates), and fatty acids.

After leaving the acidic environment of the stomach where simple molecules like water and alcohols are absorbed, food enters the more basic environment of the small intestines. The small intestine is basically a 22-foot long tube where, with help from enzymes secreted by the liver and pancreas, the more complex amino acids, carbs, and fatty acids are absorbed through the walls and into the bloodstream.

Glycolysis and β-oxidation: Two ways cells use macronutrients for power

Overview of Glycolysis:

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Once the nutrients from our food has been broken down into small molecules and absorbed into the blood in the small intestine, they are shuttled to the liver through the hepatic portal vein. This vein goes straight from the intestines to the liver. This is important because in addition to clearing compounds from the blood, like alcohol or other toxins, the liver is the bodies “nutrient factory.” Once the nutrients we eat are broken down into monomers (individual molecules), the liver puts them back together to make different chemicals and compounds the body needs to function. In our case, we will focus mainly on carbs and fatty acids.

Structure of Simple (top four) and Complex (bottom) Carbohydrates:

Carbs, such as sucrose (table sugar) or lactose (in milk and other dairy products), are broken down into individual glucose molecules. Glucose is used by all the cells in your body as fuel when broken down through the process of glycolysis to produce adenosine triphosphate or ATP. Cells use the energy stored in the bonds of ATP to power the various reactions and jobs they have. In addition to the previously mentioned functions of the liver, it also acts as your body’s glucose storage by reassembling individual glucose molecules into strings of glucose molecules called glycogen.

At times when the glucose concentration of the blood is low the body is also able to breakdown fat molecules in the form of fatty acids through a process known as beta-oxidation (β-oxidation). Fat is stored as triglycerides which consist of three fatty acids bonded to a glycerol molecule. When the fatty acids are removed from the triglyceride molecule and oxidized they form what are known as ketone bodies or ketones. In addition to using glucose, ketones can also be used to generate energy in the form of ATP to be used by the cell.

Overview / Big Picture

• Humans get energy from eating other animals and plants.
• We extract the energy from food by using enzymes in our saliva, stomach, small intestines, liver, and pancreas.
• Once nutrients are absorbed in the small intestine, they pass through the bloodstream to the liver where they can be reassembled into molecules required by the body.
• Carbohydrates are broken down through glycolysis to generate energy in the form of ATP.
• Fat molecules can also be used for energy when oxidized into ketone bodies.

If you’ve made it this far, I want to thank you! Please let me know what you think in the comments below! If you loved it tell me, if you hated it TELL ME and I’ll try to change some stuff up. Was this too much information or should I nerd out a little more? If you have any requests or suggestions please tell me! Thank you again for reading, I’ll try my best to get the next installment out quicker in which I will talk about the Ketogenic Diet and its theoretical impacts on cancer survival times.

Until next time,
Kory

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Image Credits

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