The fact that your body is able to turn a wide variety of molecules into usable energy is astonishing. This would be equivalent to being given wood, gasoline, and wind and asked to convert it into usable energy simultaneously. While these are possible on their own, the fact that the body is able to do it all without you ever thinking about it is astonishing.
Below is a look at how your cells traditionally get energy levels and how proteins can also be utilized as a source of energy. Understanding the metabolic pathways of the body can allow you to better understand your nutrition and what your body needs when it needs it.
How cells get energy
The human body is composed of trillions of cells that all need to obtain energy to survive. Nearly every cell in your body contains an organelle known as the mitochondria which have the sole purpose of converting glucose into adenosine triphosphate (ATP). ATP is the energy molecule that cells utilize to survive and perform normal functioning. Muscle cells for instance utilize ATP to facilitate movement.
The reliance on ATP means that the mitochondria play a vital role in the survival and function of the cells in your body. This dependence on ATP is a large reason why people are able to take energy from multiple sources in their diet. Throughout evolutionary history, there may have been times when protein was plentiful and carbohydrates were scarce or the other way around. Having the ability to get ATP from multiple sources ensures that you are able to survive.
Mitochondria
The mitochondria have an inner membrane and an outer membrane. The membranes are selectively permeable and only allow specific molecules to pass through them. The selective permeability paired with membrane proteins is what allows for cellular respiration to occur in the mitochondria.
Cellular respiration
Cellular respiration begins when a cell obtains glucose from the bloodstream. The glucose molecule is subsequently broken down and modified where it is able to enter the mitochondria. While in the mitochondria the molecule is broken down further and manipulated by enzymes on the inner membrane. Each manipulation leads to the pumping of hydrogen ions into the space between the membranes known as the intermembrane space. The high concentration of hydrogen ions essentially pressurizes the intermembrane space and a membrane protein known as ATPase releases this pressure while simultaneously making ATP.
The entire process follows a cycle and allows for the continuous production of ATP. By harnessing the energy found between carbon bonds, the mitochondria are able to effectively produce ATP at a level to sustain life and your entire being.
Is protein a source of energy?
When people think of protein, they typically don't think of how it is used for energy but rather think of it in regards to how it is utilized in muscle growth. While proteins are important in muscle development and growth, they can also be utilized as a source of energy.
Typically proteins are utilized by cells for building new structures or enzymes, but in certain cases, protein can be used as a source of energy. If there is high protein in abundance and it is being underutilized, or in the case that carbohydrates are unavailable, the body will begin utilizing protein as a source of energy.
Proteins can enter the cellular respiration pathway but they require specific steps to allow them to do so. The building block of proteins are amino acid and there are 20 different amino acids that are utilized in the human body. Amino acids vary significantly in structure so there are multiple pathways that they can take to get into the mitochondria.
As stated previously, the mitochondria have a highly specific membrane that only allows certain molecules to enter. Amino acids are converted into one of these molecules which allows it to seamlessly enter the mitochondria and produce ATP.
Since amino acids typically don’t have many carbon bonds, these molecules can be utilized to produce glucose in a process called gluconeogenesis. Through this conversion, amino acids can effectively be utilized as a form of energy throughout the body in the form of glucose. Areas like the brain are only able to utilize glucose as a source of energy. The ability to produce glucose through the use of proteins is a great fail-safe in the event you don’t eat any carbohydrates.
Factors that can reduce cellular energy production
The cellular metabolism system is highly specific and is the result of millions of years of evolution. While highly robust, there are factors that can reduce mitochondrial effectiveness. One of these is the decreased level of CoQ10 within the mitochondrial membrane. CoQ10 is an antioxidant molecule that helps protect the mitochondrial membrane from free radicals. Without CoQ10 the mitochondrial membrane can experience oxidative stress which can decrease its efficiency of ATP production.
Decreases in CoQ10 can come about due to aging and other factors. Decreased efficiency of the mitochondria can affect carbohydrates, fatty acids, and essential amino acid equally since the conversion of molecules to ATP is slowed.